Texas
Transportation
Institute
Emissions of Mexican-Domiciled
Heavy-Duty Diesel Trucks Using
Alternative Fuels
TEXAS TRANSPORTATION INSTITUTE
THE TEXAS A&M UNIVERSITY SYSTEM
COLLEGE STATION, TEXAS
Sponsored by the Alamo Area Council of Governments
With Funding from the EPA Region 6
October 2007
Emissions of Mexican-Domiciled Heavy-Duty
Diesel Trucks Using Alternative Fuels
By
*Josias Zietsman, Ph.D., P.E., *Mohamadreza Farzaneh, Ph.D., **John M. Storey, Ph.D.,
*Juan C. Villa, *Mark Ojah, *Doh-Won Lee, Ph.D., and ***Peter Bella
*
Texas Transportation Institute
** Oak Ridge National Laboratory
*** Alamo Area Council of Governments
Sponsored by
Alamo Area Council of Governments with funding from EPA Region 6
October 2007
TEXAS TRANSPORTATION INSTITUTE
The Texas A&M University System
College Station, Texas 77843-3135
4
TABLE OF CONTENTS
1. Introduction ............................................................................................................................... 1
1.1 Purpose of the Study ............................................................................................................. 1
1.2 Background ........................................................................................................................... 1
U.S.-Mexico Cross Border Trucking: Regulations and Status ............................................... 2
1.3 Cross-Border Trucking Process ............................................................................................ 4
FAST Program ........................................................................................................................ 4
1.4 Potential for Trucking beyond the U.S. Commercial Zone .................................................. 5
1.5 Non-Attainment Challenges.................................................................................................. 6
1.6 Alternative Fuels ................................................................................................................... 6
1.7 Overview of Testing Procedure ............................................................................................ 7
2. Study Methodology ................................................................................................................... 9
2.1 Test Equipment and Procedure ............................................................................................. 9
Gaseous Emissions Measurement ........................................................................................... 9
PM Measurement .................................................................................................................. 10
MSATs .................................................................................................................................. 13
2.2 Test Protocol ....................................................................................................................... 14
Emissions Measurement ....................................................................................................... 14
Fuel Purging .......................................................................................................................... 15
2.3 Vehicle Fleet Profile and Sample Selection........................................................................ 16
2.4 Test Load ............................................................................................................................ 18
2.5 Test Site .............................................................................................................................. 18
2.6 Drive Cycle Development................................................................................................... 19
Drayage Drive Cycle............................................................................................................. 20
Long-Haul Drive Cycle......................................................................................................... 20
Drive Cycle Replication ........................................................................................................ 21
2.7 Data Handling ..................................................................................................................... 22
Data Conversion.................................................................................................................... 22
Data Extraction ..................................................................................................................... 23
Data Cleaning........................................................................................................................ 23
2.8 Fuel Analysis ...................................................................................................................... 24
3. Results ...................................................................................................................................... 27
3.1 Idle Tests ............................................................................................................................. 28
Gaseous Emissions Results ................................................................................................... 28
PM Emissions Results........................................................................................................... 33
MSAT Analysis .................................................................................................................... 35
Discussion of Idling Emissions Results ................................................................................ 38
3.2 On-Road Tests .................................................................................................................... 39
Gaseous Emissions Results ................................................................................................... 39
PM Emissions Results........................................................................................................... 40
4. Conclusions .............................................................................................................................. 43
Potential for Trucking beyond the U.S. Commercial Zone ...................................................... 43
Emissions Testing ..................................................................................................................... 43
Test Protocol ......................................................................................................................... 43
NOx Emissions ..................................................................................................................... 43
iii
HC Emissions........................................................................................................................ 43
CO Emissions........................................................................................................................ 44
CO2 Emissions ...................................................................................................................... 44
PM Emissions ....................................................................................................................... 44
5. Recommendations ................................................................................................................... 48
6. Acknowledgements ................................................................................................................. 50
APPENDIX A .............................................................................................................................. 52
APPENDIX B .............................................................................................................................. 57
APPENDIX C .............................................................................................................................. 66
iv
LIST OF FIGURES
Figure 1. Northbound Commercial Border Crossing Process. ....................................................... 4
Figure 2. SEMTECH-DS PEMS unit on the left and installation in the trailer on the right......... 10
Figure 3. Installed OEM-2100 Montana CATI Unit. ................................................................... 11
Figure 4. Exhaust flow meter installations. .................................................................................. 12
Figure 5. Relationship Between MSATs and Diesel-Related Compounds. ................................. 13
Figure 6. Flow Chart of the Test Protocol. ................................................................................... 14
Figure 7. Fuel Purging Procedure and Auxiliary Fuel Tank. ........................................................ 15
Figure 8. Drayage Truck Age Frequency Based on 2006 TTI Survey. ........................................ 16
Figure 9. The Loaded Trailer Used for Testing On-Road Emissions. .......................................... 18
Figure 10. Equipment and Loaded Trailer at Test Site, Laredo, Texas. ....................................... 18
Figure 11. Satellite Image of Test Area. ....................................................................................... 19
Figure 12. Laredo’s Drayage Drive Cycle. ................................................................................... 20
Figure 13. Long-haul Drive Cycle. ............................................................................................... 21
Figure 14. Drive Cycle Replication. ............................................................................................. 21
Figure 15. Proper Alignment of Time Alignment Graph. ............................................................ 22
Figure 16. Improper Alignment of Time Alignment Graph. ........................................................ 22
Figure 17. Fuel Showing Contaminants. ...................................................................................... 26
Figure 18. Gaseous Emissions Results for Low-Idling Test at 600 rpm. ..................................... 29
Figure 19. Gaseous Emissions Results for High-Idling Test at 1200 rpm.................................... 30
Figure 20. PM Emissions from Mexican Trucks. ......................................................................... 33
Figure 21. Diesel PM Emissions for the Laredo trucks. ............................................................... 34
Figure 22. Formaldehyde and Acetaldehyde Emissions for all 10 Laredo Trucks. ...................... 36
Figure 23. Formaldehyde and Acetaldehyde Emissions by Model Year...................................... 37
Figure 24. Drayage Cycle — Emissions Rates and Emissions Index........................................... 41
Figure 25. Long-Haul Cycle — Emissions Rates and Emissions Index....................................... 42
LIST OF TABLES
Table 1. Information on Test Vehicles and Emissions Standards. ............................................... 17
Table 2. Test Vehicle Details. ....................................................................................................... 17
Table 3. Specifications of the Tested Fuels. ................................................................................. 25
Table 4. PM Emissions Results. ................................................................................................... 35
v
1. Introduction
1.1 Purpose of the Study
The majority of truck crossings from Mexico into the U.S. occur at Ports of Entry (POEs) in
Texas. The U.S.-Mexico border is scheduled to be opened to transnational trucking in the near
future. When this occurs, it will create new long-haul transportation opportunities for Mexicandomiciled motor carriers.
Mexican heavy-duty diesel trucks currently engaged in border drayage or domestic Mexican
long-haul service may be used to transport goods to multi-modal transportation hubs or other
facilities in San Antonio, Houston, or beyond. It is, therefore, important to consider appropriate
emissions reduction strategies for such trucks to ensure that their emissions impacts on
nonattainment, early action compact, and near nonattainment areas are minimized. This study
focuses on one such strategy; the use alternative fuels to power heavy-duty diesel trucks.
The overall goal of this study was to quantify emissions produced by Mexican trucks operating
on standard diesel and alternative fuels. The following tasks were conducted to achieve this goal.
Assess the likelihood that Mexican drayage and long-haul trucks will operate beyond the
current border commercial zone if, and when, this is permitted.
Determine the fleet profiles (makes, models, and age) of Mexican drayage and long-haul
trucks expected to operate in the U.S.
Identify the driving patterns (drive cycles) of these drayage and long-haul trucks.
Measure the emissions impact of using conventional Mexican diesel and alternative fuels
such as ultra-low sulfur diesel (ULSD fuel) and biodiesel fuel.
Document the findings, conclusions, and recommendations.
Vehicle testing was conducted near the Colombia Commercial Bridge, just outside of Laredo,
Texas. A sample of five Mexican drayage trucks and five Mexican long-haul trucks were
selected for testing. Each truck was subjected to long-haul and drayage drive cycles while
operating with three different fuel types and pulling a trailer that had been loaded to a specified
weight. Emissions data was collected using portable emissions measurement system (PEMS)
equipment.
1.2 Background
Over 5 million trucks crossed from Mexico into the U.S. in 2005. Whether measured by weight
or value, U.S.-Mexico surface freight transportation is dominated by the truck mode. The need to
measure pollutants emitted by Mexican trucks stems in part from the planned liberalization of
U.S.-Mexico cross-border trucking regulations.
Currently, the operation of Mexican motor carriers in the U.S. is confined to a narrow
commercial zone that generally extends up to 20 miles beyond the border (the extent of the
commercial zone depends on the size of the border community). This restriction is one of the
fundamental reasons why Mexican truck shipments into the U.S. are required to use a drayage or
transfer tractor. Drayage trucks pick up northbound trailers on the Mexico side of the border and
1
shuttle them into the U.S. commercial zone. There, they are transferred to a U.S. carrier that
delivers them to the final destination. Over the years, this inefficient border crossing process has
been the subject of considerable debate and litigation. The following section provides a concise
summary of regulatory developments with respect to direct Mexico-U.S trucking.
U.S.-Mexico Cross Border Trucking: Regulations and Status
Changes to the North American Freed Trade Agreement (NAFTA) trucking provisions were
intended to streamline the complex, costly, and time-consuming process of using drayage trucks
to transport cargo a short distance across the U.S.-Mexico border. By removing regulatory
barriers, seamless and efficient one-carrier trucking operations such as those between the U.S.
and Canada were envisioned. Restrictions on long-haul trucking between Mexico and U.S.
border states were to be phased out beginning in December of 1995. By 2000, reciprocal
nationwide trucking access was to be authorized. Implementation of these provisions has been
postponed on multiple occasions and for a variety of reasons.
In 1995, the U.S. Congress upheld the moratorium on direct long-haul trucking from Mexico to
the U.S., arguing that Mexico’s truck safety regulations could not adequately ensure the safety of
its commercial drivers and carriers. Less stringent safety regulations and enforcement practices
in Mexico were deemed a potential safety risk to the U.S. public. Continuation of the moratorium
in subsequent years led the Mexican government to request that a NAFTA arbitration panel rule
on the matter.
In 2001, the arbitration panel concluded that Mexico’s less rigorous truck safety inspection
system was inadequate justification for the U.S.’ blanket refusal to allow Mexican carriers to
operate beyond the U.S. commercial zone. However, it also declared that a more comprehensive
application process for Mexican carriers applying to operate in the U.S. was acceptable in light
of disparate U.S. and Mexican truck laws, regulations, and procedures.
In the fall of 2001, a newly-elected U.S. administration vowed to comply with the panel’s
findings. Its proposed action plan called for the creation of separate application processes for
Mexican motor carriers seeking to continue operating within the U.S. commercial zone (OP-2
authority) and those seeking authority to travel beyond the U.S. commercial zone to cities such
as San Antonio and Houston (OP-1 authority). Additionally, it mandated the development of an
enhanced monitoring system and enforcement regime to ensure that Mexican carriers operating
anywhere in the U.S. would be in compliance with local laws and regulations. These
recommendations were intended to prepare U.S. agencies for the opening the border to qualified
Mexican carriers by January 2002.
Readiness assessments conducted by the U.S. Department of Transportation (U.S. DOT)
Inspector General and other public agencies identified several deficiencies in the U.S.’
preparedness to accommodate Mexican long-haul movements. However, by November 2002,
these concerns were largely addressed and the moratorium on Mexican trucking beyond the U.S.
commercial zone was officially lifted. However, legal challenges by unions, non-profit
organizations, and trucking associations in the U.S. were subsequently launched and continued to
delay the opening of the southwest border. These groups contended that the U.S. government did
2
not conduct an adequate environmental review to assess the impact of liberalized cross-border
trucking regulations on U.S. air quality.
In January 2003, the 9th Circuit Court of Appeals in California ruled that the U.S. government’s
decision to allow direct U.S.-Mexico trucking was ―arbitrary, capricious and disregarded
established environmental laws.‖ The ruling required further environmental reviews to be
conducted prior to the implementation of liberalized cross-border trucking regulations between
the U.S. and Mexico. Although more detailed environmental studies were initiated, they were
halted in June 2004 when the U.S. Supreme Court overturned the 9th Circuit Court of Appeals’
decision and paved the way for Mexican motor carriers to apply for operating authority beyond
the U.S. commercial zone.
Despite this ruling, direct trucking from the interior of Mexico to cities such as San Antonio and
Houston has yet to become established. The remaining regulatory obstacle was a sovereignty
dispute between the countries. To qualify for OP-1 authority, U.S. law requires that Mexican
trucks and drivers be certified by U.S. regulatory personnel at their facilities in Mexico. The
Mexican government’s refusal to approve these inspections left the issue at a stalemate for twoand-one-half additional years.
On February 23, 2007, the U.S. and Mexican governments announced that they had reached a
resolution to the cross-border trucking impasse. The agreement calls for a one-year pilot project
involving up to 100 Mexican and 100 U.S. trucking firms that wish to engage in direct long-haul
movements across the border and beyond the commercial zone. Mexican carriers must undergo
safety audits by U.S. inspectors in Mexico; meet all safety, environmental, insurance, homeland
security, and other regulations imposed on U.S. trucking firms; and pay all applicable U.S. state
and federal taxes and registration fees. Mexican truckers must also pass a safety review to travel
beyond the U.S. commercial zone. This includes verification of their driving history, commercial
driver’s license, medical certificate, and compliance with hours-of-service regulations.
According to the U.S. DOT, direct door-to-door international movements are expected to begin
in May 2007. The pilot project will be evaluated after one year, at which time a decision
regarding the future of the initiative will be made.
Delays in the implementation of NAFTA’s trucking provisions have provided an opportunity to
measure the potential emissions impact that Mexican trucks might have if they travel to cities in
Texas. While the provisional operating authority has made a gradual shift toward these types of
movements possible, the extent to which Mexican carriers will choose to pursue cross-border
authority also depends on a number of private-sector considerations.
3
1.3 Cross-Border Trucking Process
The current border crossing process requires a shipper in Mexico to file shipment data with both
Mexican and U.S. agencies, prepare paper and electronic documents, and contract a drayage firm
to transport the goods from one country to the other. After the driver, drayage tractor, and cargo
begin the actual border crossing process, the movement is subject to inspections at three
inspection areas:
Mexican export lot;
U.S. federal compound; and
state safety inspection facility.
Figure 1 illustrates the main activities in the northbound border crossing process.
Figure 1. Northbound Commercial Border Crossing Process.
FAST Program
One program that can potentially expedite the border crossing process and, therefore, might
facilitate cross-border movements of long-haul Mexican trucks is the Free and Secure Trade
(FAST) initiative. The Department of Homeland Security (DHS) and Customs and Border
Protection (CBP) have implemented several security programs at U.S. land ports of entry. The
FAST initiative is designed to provide incentives for supply chain security by offering expedited
clearance to carriers and importers enrolled in the Customs Trade Partnership Against Terrorism
(C-TPAT). FAST shipments use a special booth and FAST-only lane at the international bridges.
Non-FAST–certified movements do not adhere to C-TPAT security protocol and take longer to
4
process. These movements are also expected to experience secondary inspections and potential
unloading of the trailer for detailed inspection.
The time required for a shipment to make the complete trip from the yard or the manufacturing
plant in Mexico to the exit of the state inspection facility in the U.S. depends on a variety of
factors, including: secondary inspections, number of inspection booths in service, traffic
volumes, time of day, nature of cargo, and C-TPAT/FAST certification. There is duplication
with regard to safety inspections, as U.S. federal and state agencies perform similar safetyrelated revisions of every truck and driver that crosses from Mexico into the U.S.
1.4 Potential for Trucking beyond the U.S. Commercial Zone
Through an examination of Mexican and U.S. trucking practices and a series of interviews with
Mexican trucking interests engaged in the transport of NAFTA freight (custom brokers, drayage
companies, and 10 long-haul trucking companies), the study team determined that most Mexican
long-haul carriers do not currently cross their trucks into the U.S. commercial zone and would be
reluctant to change that aspect of their operations. Many Mexican drayage firms currently
crossing the border do not intend on pursuing contracts beyond the U.S. commercial zone, even
if such movements are permitted. The following issues were cited by these groups as reasons
why they are reluctant to apply for operating authority to send their vehicles and drivers into the
U.S. interior.
1. Business inertia: Current service alliances between Mexican and U.S. trucking firms
enable firms in each country to focus on their own market. The lack of an established
sales presence in the U.S. on the part of Mexican carriers may reduce their backhaul
opportunities beyond the U.S. commercial zone. The U.S. and Mexico also have different
accounting systems and trucking business practices. While often costly, time consuming,
and inefficient for the customer, the status quo border-crossing system serves the interests
of many carriers. The inertia of current business practices is perceived to be strong and
may require several years to change.
2. Influence of third parties: Third parties such as customs brokers and freight forwarders
can wield substantial influence over shippers and the logistics of cross-border
movements. If these stakeholders feel their interests are threatened by a liberalization of
cross-border trucking provisions, they may try to prevent adoption of them.
3. Concerns about law enforcement: Mexican fleet owners feel that their vehicles and
drivers would be targeted by local U.S. law enforcement beyond the U.S. commercial
zone.
4. Loss of drivers: The U.S. long-haul trucking industry has suffered from acute driver
shortages in recent years. Mexican fleet owners fear that their drivers, who are
accustomed to working long hours for little pay, may be lured away by relatively
attractive pay and working conditions in the U.S. trucking industry.
5. Border delays: Mexican carriers with late model trucks cannot afford to idle their
expensive assets in border bottlenecks and congestion.
6. Higher operating costs: Insurance and other operating costs are higher in the U.S. and
represent an obstacle to Mexican carriers trying to enter this market.
5
7. Higher equipment costs: Higher interest rates in Mexico prevent Mexican fleet owners
from making the equipment investments they feel are necessary to operate competitively
in the U.S. market.
8. Application process: Some Mexican carriers are discouraged from applying for crossborder operating authority by a lengthy, rigorous, and potentially costly application,
audit, and documentation process that they may not pass.
9. Language barriers: Language or cultural barriers may preclude or dissuade some
Mexican drivers from applying for operating authority beyond the U.S. commercial zone.
10. Potential maintenance costs: Mexican drayage operations typically utilize older
vehicles, which may be susceptible to costly maintenance if they break down while
abroad.
These and related issues were considered by the study team, and a subset of fleet owners who
have applied for or expressed an interest in obtaining authorization from the U.S. Federal Motor
Carrier Safety Administration (FMCSA) to operate beyond the U.S. commercial zone were
identified.
1.5 Non-Attainment Challenges
When examining the cross–border trucking between Mexico and Texas, the San Antonio region
is of particular significance. Because it is a major multi-modal hub that is relatively close to the
border region, it may be a feasible destination for Mexican motor carriers interested in crossborder operations. The San Antonio area is in ―deferred‖ non-attainment status for the National
Ambient Air Quality Standards’ (NAAQS) eight-hour ozone standards. The deferral of nonattainment status is the result of a 2002 Early Action Compact (EAC) between the local
governments in the San Antonio region working together as the Air Improvement Resources
(AIR) Committee of the Alamo Area Council of Governments (AACOG), the US Environmental
Protection Agency (EPA) and the Texas Council on Environmental Quality (TCEQ). The EAC
allows the San Antonio region time until the end of December 2007 to achieve the stricter eighthour ozone standards set by the NAAQS.
Under these circumstances, it is possible that Mexican trucks that do not have strict emissions
controls may have an adverse effect on the air quality in the San Antonio region. Thus
quantification of the emissions of ozone precursors and other pollutants is of special relevance.
Emissions control strategies such as low emission alternative fuels for Mexican trucks crossing
into the U.S. can play a positive role in addressing air quality concerns in the San Antonio area.
1.6 Alternative Fuels
Another concern raised by cross-border trucking is related to the quality of fuel sold in Mexico
as compared to fuels used in the U.S. Due to the diesel prices trend in the US-Mexico border
region1 (Figure A.2 in Appendix A), it is reasonable to assume that Mexican trucks engaged in
cross-border trucking would make use of fuel sold in Mexico. However, this may result in a
change in emissions quality that could be offset using a different fuel mix. Thus, this study
measures the emissions for Mexican trucks using three types of fuel – the standard diesel
1
Mexican Department of Property and Public Credit, Nota Technica Sobre Los Combustibles de Ultra Bajo Azufre,
November 2006.
6
available in Mexico, ULSD fuel (mandated by the U.S. Environmental Protection Agency [EPA]
for use in 2007 and later model trucks in the U.S.), and a biodiesel mix (20 percent biodiesel fuel
and 80 percent ULSD fuel). Detailed description of the fuels used is provided later in this
document.
1.7 Overview of Testing Procedure
The procedure involved testing emissions of carbon monoxide (CO), carbon dioxide (CO2),
oxides of nitrogen (NO and NO2 – collectively referred to as NOx), total hydrocarbons (THC),
and particulate matter (PM). Sampling was also performed for mobile-source air toxics
(MSATS) under idling conditions. The existing vehicle fleet participating in cross-border
trucking was first profiled and a representative sample of trucks was selected. Testing was
conducted for the three different fuel types on the selected trucks following pre-determined drive
cycles. The research team used two PEMS units for the testing, which was conducted at the
Colombia Border Bridge near Laredo. The remainder of the report is divided into chapters that
describe the study methodology, results, and conclusions and recommendations.
7
2. Study Methodology
2.1 Test Equipment and Procedure
The research team used two types of PEMS units for the testing. A SEMTECH-DS unit was used
to measure gaseous emissions such as CO, CO2, NOx, and THC, while an OEM-2100
―Montana‖ System was used for measuring PM. For measuring PM during the idling tests, a
Tapered Element Oscillating Microbalance (TEOM) deployed by Oak Ridge National
Laboratory (ORNL) was used. For air toxics during the idle tests, Solid Phase Extraction (SPE)
cartridges were used.
Gaseous Emissions Measurement
The SEMTECH-DS unit includes a set of gas analyzers, an engine diagnostic scanner, a Global
Position System (GPS), an exhaust flow meter, and embedded software.
The gas analyzers measure the concentrations of NOx (nitric oxide, NO, and nitrogen dioxide,
NO2), THC, CO, CO2, and oxygen (O2) in the vehicle exhaust. The engine scanner was
connected to the vehicle engine control module (ECM) via a vehicle interface (VI) (where
available) and provided vehicle speed, engine speed (RPM), torque, and fuel flow. The
SEMTECH-DS uses the Garmin International, Inc.’s GPS receiver model GPS-16 HVS to track
the route, elevation, and ground speed of the vehicle on a second-by-second basis.
The SEMTECH-DS uses the SEMTECH electronic exhaust flow meter (EFM) to measure the
vehicle exhaust flow. Its post-processor application software uses this exhaust mass flow
information to calculate exhaust mass emissions for all measured exhaust gases. The
SEMTECH-DS uses embedded software, which controls the connection to the external
computers via a wireless or Ethernet connection to provide the real-time control of the
instrument. A Panasonic Toughbook laptop was used to connect to the SEMTECH-DS via
Ethernet and to control the unit. Figure 2 shows the SEMTECH-DS PEMS unit as well as how it
was installed in the test trailer.
9
Figure 2. SEMTECH-DS PEMS unit on the left and installation in the trailer on the right.
PM Measurement
The PEMS unit used to collect PM was the OEM-2100 ―Montana‖ system manufactured by
Clean Air Technologies International, Inc. (CATI). The OEM-2100 system is comprised of gas
analyzers, a PM measurement system, an engine diagnostic scanner, a GPS, and an on-board
computer. For this study only the PM measurement system was used. The PM measurement
capability includes a laser light scattering detector and a sample conditioning system. The PM
mass concentrations were converted from the light scattering scales internally using present
parameters by the CATI unit. Using the exhaust flow rates produced by the SEMETCH-DS unit,
PM mass emissions rates are calculated from the concentrations.
It should be noted that engine exhaust particles generally have three different size ranges: 3-30
nm, 30-500 nm, and > 500 nm (or, 0.5 μm). Most particles produced in a diesel engine have
particle sizes of 0.5 μm or less2. This size is comparable to the PM-2.5 (2.5 μm or less) particle
size as regulated by the EPA3.
Figure 3 shows a photo of the CATI PEMS unit.
2
Kittleson, et.al. ―On-Road Evaluation of Two Diesel Exhaust After-treatment Devices.‖ Journal of Aerosol
Science. 37:1140-1151, 2006.
3
U.S. EPA, http://epa.gov/air/criteria.html, accessed 4/24/2007.
10
Figure 3. Installed OEM-2100 Montana CATI Unit.
In addition to the transient PM measurements obtained using the CATI PEMS unit, the ORNL
team also collected PM sampling during idling modes. All ORNL’s PM and MSAT (aldehyde)
samples were obtained by diluting the exhaust with a microdilution system used in previous
studies on idling trucks.4 The exhaust was transferred through a 15-inch long, heated (250 °C)
line to the microdilution tunnel from a probe in the outlet of the SEMTECH-DS exhaust flow
meter.
To determine dilution ratio, NOx measurements were made for both the raw and diluted exhaust.
The dilution ratio was maintained at 8:1 through the testing to enable the collection of samples
relatively quickly. Filters still required 15 minutes of sampling, however, to accumulate enough
mass for measurement. Compressed air for the dilution tunnel was obtained by compressing the
outside air with an oil-less air compressor, then drying and HEPA-filtering the air with a
membrane dryer before it reached the microdilution tunnel.
Both a continuous and integrated approach was used to measure PM. For continuous
measurements, the TEOM (Thermo Scientific Model 1105) was used to measure the diluted
exhaust for PM mass. Flows were set to 2.5 lpm. For each condition, PM was collected on a preweighed 70mm Teflon™-coated quartz fiber filter (Pall EMFAB TX40) for 15 minutes at a flow
rate of ~50 lpm. The exposed filters were returned to ORNL, re-equilibrated in the weighing
chamber and re-weighed.
4
Zietsman, J., J.C. Villa, T.L. Forrest, and J.M. Storey. Mexican Truck Idling Emissions at the El Paso - Ciudad
Juarez Border Location. Southwest Region University Transportation Center, The Texas A&M University System,
College Station, Texas, 2005.
11
Figure 4 shows the exhaust flow meter installation. It shows the PEMS sampling line and
sampling cart with microdilution tunnel and TEOM.
Microdilution Tunnel
TEOM
PEMS
Sampling Line
Heated Line to
Dilution Tunnel
Figure 4. Exhaust flow meter installations.
12
MSATs
MSATs have become increasingly important in recent years as states and air quality districts are
now forced to address them along with other criteria pollutants. The EPA has identified 21
MSATs, and the following figure illustrates the interrelationship between individual compounds
that are MSATs and the classes of substances also listed as MSATs.
Figure 5 shows the subset (of the 21 MSAT compounds identified by EPA) that were measured
or attempted to be measured in this study.
MSATs
Semivolatile organics
Volatile organics
Particulate Matter (PM)
Diesel Exhaust Organic Gases
Formaldehyde,
Acetaldehyde*
1,3 Butadiene
Acrolein*
Diesel PM*
Metals
POM (polycyclic
organic matter)
Benzene,
Naphthalene
PAHs
Figure 5. Relationship Between MSATs and Diesel-Related Compounds.
(Compounds marked with an asterisk were measured in this study)
As shown in Figure 5 this study focused on diesel PM, formaldehyde, and acetaldehyde. These
MSATs are very heavily associated with truck traffic, and in particular, large numbers of idling
trucks. To simulate typical idle conditions, while still enabling MSAT sampling, two idle speed
conditions were measured – low idle and high idle. The main focus was on idling because it is
anticipated that this mode creates the highest levels of MSATs and can most effectively be
addressed with possible emissions reduction strategies.
MSATs were measured for idling conditions, with a warm engine. Fuel changes were performed
such that two idle runs could be done sequentially, and the exhaust temperature was allowed to
cool after the previous cruise.
Waters DNPH SPE cartridges (no.WAT37500) were used to collect samples for aldehyde
analysis from the diluted exhaust. Flow rate was set to 1 lpm. Samples were taken for 15
minutes, for a total of 15 l/cartridge. The cartridges were eluted immediately after sampling with
3 ml of acetonitrile, and the effluents stored in a refrigerator for later analysis by high
performance liquid chromatography (HPLC) using the analytical method provided by Waters.
13
2.2 Test Protocol
Emissions Measurement
The study team developed a test protocol that would provide the best opportunity to test
emissions differences resulting from using different fuel types. The effect of fuel mix was
captured by driving the test vehicles equipped with each fuel mix according to the developed
drayage and long-haul drive cycles. To maintain consistency between each run, a professional
truck driver drove the vehicle for all test runs. Each test scenario included two runs and for each
run the emissions, engine, and speed data were collected on a second-by-second basis. In
addition to the road tests, each vehicle was tested in two different idle modes — low idle at 600
to 700 rpm, and high idle at 1200 rpm.
Figure 6 shows a flow diagram illustrating the test protocol used. Each on-road test scenario was
repeated two times resulting in 210 total tests including the idle tests (10 trucks × 3 fuels × [2
runs × 2 cycles + 3 idle] = 210).
Test Scenarios
Drayage
Tru
D 01*
D 02*
cks
D03*
Long-haul
Tru
D04*
LH 01**
LH 02
cks
LH 03
LH 04
D05*
Testing Process for All Trucks
ULSD
B20
PEMEX
Max Sulfur 15 ppm
Biodiesel
Max Sulfur 500 ppm
Drayage Cycle 1
Drayage Cycle 2
Long-haul Cycle 1
Long-haul Cycle 2
Low Idle
* D 01: Drayage Truck 1
** LH 01: Long-haul Truck 1
High Idle
Figure 6. Flow Chart of the Test Protocol.
14
LH 05
Fuel Purging
Because each truck was tested with three different fuel types, a fuel purging procedure was used
to ensure that the truck engine and fuel system were completely purged of one fuel type before
the truck was tested using the next fuel type. In a regular diesel engine set-up, there is a two-way
connection between the fuel tank and the engine. An inlet line brings fuel from the fuel tank to
the engine, and a return line from the engine takes unconsumed fuel back into the tank for recirculation.
In the test set-up, the fuel tank was intercepted by an auxiliary fuel tank. The fuel purging was
performed by running approximately two gallons of the new fuel through the fuel system and
having the outlet line dump the fuel into a separate container. After enough of the new fuel
circulated through the system, all the old fuel was replaced with the new fuel. After the purging
was completed, the outlet connection was restored to the auxiliary fuel tank and the vehicle was
ready for testing. This purging procedure was repeated every time the test fuel was changed.
Figure 7 shows the location of the auxiliary fuel tank as well as the inlet and return lines.
Auxiliary Fuel
Tank
Fuel Lines
Figure 7. Fuel Purging Procedure and Auxiliary Fuel Tank.
15
2.3 Vehicle Fleet Profile and Sample Selection
Based on carrier interviews and the literature review, the research team determined that the fleet
of Mexican-domiciled trucks expected to travel to areas in Texas in a liberalized cross-border
trucking environment would be long-haul trucks, although drayage trucks might also participate
in movements to cities such as San Antonio. The team therefore decided to select a mix of longhaul and drayage trucks. By testing drayage trucks in addition to long-haul trucks there is also an
opportunity to estimate the emissions impact of the border region as well as for longer distances.
The sample of test vehicles was based on existing fleets (percentage of trucks by model year)
obtained from Mexican long-haul companies interviewed by the study team, and a survey of
northbound drayage vehicles passing through the two commercial border crossing facilities at
Laredo. Figure 8 shows the 2006 survey data of the drayage truck age frequencies collected at
the Laredo border crossing.5 Figure 8 shows that 86 percent of the drayage tractors sampled were
model year 1990-2000, with mid-1990s models being the most prevalent. A survey performed by
researchers at University of California Davis6 in 2003 showed that only 8 percent of the surveyed
U.S.-domiciled trucks were older than 10 years (compared to 75 percent of surveyed Mexicandomiciled trucks in this study). UC Davis researchers found that 69 percent of the U.S.domiciled trucks surveyed were four years old or newer. Figure A.1. in Appendix A explains the
results from both surveys.
18%
16%
Proportion
14%
12%
10%
8%
6%
4%
2%
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
0%
Model year
Figure 8. Drayage Truck Age Frequency Based on 2006 TTI Survey.
5
TTI Survey. World Trade Bridge and Colombia Solidarity Bridge, 2006.
Lutset, N.P. et al. Heavy-Duty Truck Idling Characteristics: Results from a Nationwide Survey. Transportation
Research Record (1880), 29 – 38, 2004.
6
16
In addition to the model year distribution shown in Figure 8, the study team considered the
different emissions categories (periods during which heavy-duty diesel engine emissions
standards remained constant) in the selection of the testing sample. Finally, logistical
considerations such as securing Mexican trucks manufactured in specific years also influenced
the selection of test vehicles.
The EPA has set emissions standards for CO, HC, PM, and NOx for heavy-duty diesel trucks
based on the ―model year‖ or ―emissions category‖ of the vehicle. The trucks selected for
sampling represented as many emissions categories as possible. Table 1 presents the test trucks
classified by EPA’s emissions categories. The corresponding EPA emissions standards for each
category are also provided. Table 1 shows that all the categories were covered except model year
1991–1993.
Table 1. Information on Test Vehicles and Emissions Standards.
EPA Emissions Standard7 (g/bhp.hr)
Emissions category/
LongDrayage
Model Year
Haul
HC CO PM
NOx
1988-1990
0
1
1.3
15.5 0.6
6.0*
1991-1993
0
0
1.3
15.5 0.25
5.0
1994-1997
3
1
1.3
15.5 0.1
5.0
1998-2003
2
2
1.3
15.5 0.1
5.0
NOx+NMHC** = 2.4, or
2004-2006
0
1
1.3
15.5 0.1
NOx = 2.5 and NMHC=0.5
Total
5
5
* NOx standard for 1988 & 1989 model was 10.7
** NMHC – Non-Methane Hydrocarbons.
As noted in Table 1 the pool of test vehicles comprised of five long-haul trucks and five drayage
trucks. Detailed information regarding, make, model, and engine type is summarized in Table 2.
Table 2. Test Vehicle Details.
Drayage Trucks
Model year
Truck Make
Engine Make
Displacement (L)
Long-haul Trucks
Model year
Truck Make
Engine Make
Displacement (L)
7
1994
International
Harvester
DDC
12.7
1995
International
Harvester
DDC
11.1
1997
International
Harvester
Cummins
10.8
1990
Kenworth
DDC
12.7
1995
Freightliner
DDC
12.7
1999
Freightliner
Cummins
10.8
1999
2001
Freightliner
Freightliner
Cummins
10.8
Cummins
14.0
2001
Volvo
Cummins
14.0
2004
Freightliner
DDC
12.7
Diesel Net- http://www.dieselnet.com/standards/us/hd.html
17
2.4 Test Load
It was important to ensure that a consistent load was used between the various tests. For this
reason the same loaded trailer was used for every test. This trailer was loaded with rolls of paper
weighing approximately 35,000 pounds. The weight of the load, trailer, and tractor totaled
approximately 75,000 pounds, which is typical for both drayage and long-haul Mexican trucks.
Figure 9 shows a photo of the loaded trailer.
Figure 9. The Loaded Trailer Used for Testing On-Road Emissions.
2.5 Test Site
The general test site was the Colombia Commercial Bridge outside Laredo. Actual testing
occurred at two locations – the idling tests occurred inside the Department of Public Safety
(DPS) testing facility adjacent to the bridge and the transient (driving) tests occurred along a
section of the Camino Colombia Toll Road. The study team performed the installations and
stored the equipment at the DPS facility. Figure 10 shows the test sites with the instruments as
well as a test truck with the load.
Figure 10. Equipment and Loaded Trailer at Test Site, Laredo, Texas.
18
2.6 Drive Cycle Development
Because the driving characteristics of drayage and long-haul trucks are substantially different,
separate drive cycles were developed to each driving pattern.
The drive cycles were developed based on the following three criteria:
reflects typical drayage or long-haul driving conditions;
easy to follow; and
can be accomodated in the available test track.
The test track selected for this study was a 7.5 mile stretch of Camino Colombia Toll Road
between FM-1472 (Mines Road) and FM-3338 (Las Tiendas Road). The Camino Colombia Toll
Road is a 22-mile four-lane highway located north of Laredo and extends from I-35 (Mile
Marker 25) to FM-1472 (Mines Road). A toll plaza divides the study section into two
approximately equal segments – one from FM-1472 to the toll plaza with a length of 3.2 miles,
and the other from the toll plaza to FM-3338 with a length of 3.3 miles. Figure 11 shows the
study section on the map. The drayage drive cycles were conducted between FM-1472 and toll
plaza. The long-haul drive cycles were conducted between the toll plaza and FM 3338 as shown
in Figure 11. The methodology used to develop each portion of the drive cycle is described in the
next section.
Figure 11. Satellite Image of Test Area.
19
Drayage Drive Cycle
The purpose of this drive cycle was to capture the characteristics of the driving pattern for
drayage trucks from Mexico on northbound trips. Because there was no pre-existing information
on precise drayage driving patterns for these vehicles, GPS units were used to collect drive-cycle
information at the Laredo border. Three Mexican drayage trucks were equipped with GPS units
and drivers were instructed to turn on the units in the morning before they started driving and to
leave the unit on until they returned to the truck yard at the end of the day. The GPS units
recorded second-by-second speed (mph) and location (coordinate) data. The data were analyzed
and a representative drayage cycle was developed to addresses the critical driving components
during drayage trips – acceleration, deceleration, cruising, idling, and creep idling. The idle
period between each moving part of the drive cycles was set to 20 seconds to ensure stability
before the next phase began. Figure 12 shows the final drayage cycle developed for this study.
Company
to
Company
60
Border to Company
1.56 mi
50
Border Crossing
0.29 mi
1.19 mi
Speed (mph)
40
30
20
10
0
0
100
200
300
400
500
600
700
Time (s)
Figure 12. Laredo’s Drayage Drive Cycle.
Long-Haul Drive Cycle
The procedure used for developing the long-haul cycle was similar to the one used for the
drayage cycle. A long-haul truck driving from El Paso, Texas to Austin, Texas was equipped
with a GPS unit. It was found that the truck spent 93 percent of the time driving and 7 percent
idling. Figure 13 shows the final long-haul cycle developed for this study.
20
80
70
60
Speed (mph)
50
40
30
20
10
0
0
50
100
150
200
250
300
Time (s)
Figure 13. Long-haul Drive Cycle.
Drive Cycle Replication
The same professional driver was used to replicate the drive cycles. This was accomplished by
having a researcher accompany the driver and providing instructions on speeds that should be
reached at different points in time. It was also determined that this approach more closely
replicated actual driving patterns than having the driver follow exact speed profiles using
driver’s aid software. It was found that the cycles were replicated fairly well while the driver
used ―normal‖ driving behavior. Figure 14 shows an example of replicating the eastbound
drayage cycle for the same truck using the three different fuel types.
80
Drayage Cycle East Bound - ULSD
Drayage Cycle East Bound - B20
Speed (mph)
60
Drayage Cycle East Bound - PEMEX
40
20
0
0
100
200
300
Time (s)
400
500
600
700
Figure 14. Drive Cycle Replication.
21
2.7 Data Handling
This section explains the data post-processing procedure for information obtained from
SEMTEC-DS. This step is necessary to build a valid emissions database. The data screening
process includes raw data file conversion, data extraction, data synchronization, and data
cleaning.
Data Conversion
The data collected by the SEMTECH-DS were recorded in a XML file. The first step to use the
data was to convert the XML files to appropriate comma separated (CSV) format, so that
spreadsheet and data analysis software could read the data. The SENSOR Tech Post Processor
software version 4.49 was used to convert the data to CSV format.
SEMTECH-DS collects data from multiple sources such as emissions from three gas analyzers,
exhaust flow from the flowmeter, ambient air conditions from the weather probe, engine data
from ECM or OBD II connections, and speed from the GPS unit. It is important to have proper
time alignment of the exhaust flow rate and the emissions concentrations because these
parameters are combined to compute mass emissions. Time alignment must be checked for each
vehicle as a part of the standard procedure. Figure 15 and Figure 16 show examples of proper
and improper time alignment graphs.
150
200
14
12
10
8
100
6
4
50
2
0
0
50
100
Time (s)
150
0
200
Figure 15. Proper Alignment of Time
Alignment Graph.
Exhaust flow
CO2
150
14
12
10
8
100
6
CO2 (g/s)
CO2
Exhaust flow (SCFM)
Exhaust flow
CO2 (g/s)
Exhaust flow (SCFM)
200
4
50
2
0
0
50
100
Time (s)
150
0
200
Figure 16. Improper Alignment of Time
Alignment Graph.
The software also converts the raw collected data to appropriate performance measures for
analysis including fuel-specific and distance-specific emissions rates. All the necessary
corrections due to the effect of ambient temperature and humidity are considered and applied by
the software. The data files recorded by the CATI PEMS unit are in CSV format and did not
require further conversions.
22
Data Extraction
After the data has been properly formatted, the required information can be extracted. The
converted data file contained more than 200 columns of information on a second-by-second
basis. Key elements in this database were extracted and used in this study:
engine speed (if an OBD II or ECM port was available);
exhaust flow rate (SCFM);
GPS time and second-by-second vehicle speed from GPS (mph);
emissions mass rate (grams per second [g/s])
fuel-specific emissions index (gallons per kilogram [g/kg] of fuel).
Another element of data used in the study was PM mass rate from the CATI unit. This unit
recorded the PM concentration in mg/m3. This information must be first time-aligned with
hydrocarbon emissions data from the SEMTECH-DS and then converted to mass rate using the
exhaust flow rates produced by the EFM.
Data Cleaning
The process of data cleaning consisted of removing unwanted portions of the second-by-second
data assembled in the data extraction step. This included removing excessive idle segments
between the moving segments. The idle period between each moving segment was set to 20
seconds with excessive idle data removed to maintain consistency between runs.
23
2.8 Fuel Analysis
The three fuel types used in this study included ULSD fuel provided by Valero, 20 percent blend
of soy-based biodiesel with the ULSD fuel, and a diesel fuel sourced from Mexico (PEMEX
fuel).
ULSD fuel describes EPA’s new standard for the sulfur content in on-road diesel fuel sold in the
U.S. beginning in October 2005. The EPA has set the allowable sulfur content for ULSD fuel to
a maximum of 15 parts per million (ppm), which is much lower than the previous standard for
on-highway low-sulfur diesel fuel(LSD, 500 ppm).8 The EPA has introduced a set of very
stringent emissions standards for diesel engines for model year 2007 and newer. To meet these
new standards, engine manufacturers have to use new emissions control technologies that are
intolerant to sulfur. These technologies include diesel particulate filters and NOx catalysts. The
introduction of ULSD fuel is intended to serve as a technology enabler to pave the way for these
advanced sulfur-sensitive exhaust emissions control devices. In addition to on-road diesel
engines, the EPA mandated the use of these advanced emissions control technologies and ULSD
fuel for marine diesel engines in 2014 and for locomotives in 2015. The EPA has speculated that
the combination of the new emissions control technologies and ULSD fuel will substantially
reduce PM and NOx emissions from diesel engines.9,10,11
Biodiesel fuel refers to a diesel-equivalent fuel derived from biological sources such as vegetable
or animal oils, and can be readily used in diesel powered engines with little or no modification.
Blends of 20 percent biodiesel fuel with 80 percent petroleum diesel fuel ( B20 fuel) are
considered the most common biodiesel fuel blend in the U.S. B20 fuel can be used in any diesel
engine without any modification. Some engine modification might be necessary with higher
percentages of biodiesel fuel. It is the only alternative fuel to have fully completed the health
effects testing requirements (Tier I and Tier II) of the 1990 Clean Air Act Amendments. In
recent years several experimental studies have investigated the impact of biodiesel fuel on the
pollutants from diesel-powered engines. These studies are not unanimous in their conclusions,
especially in terms of changes in NOx emissions due to using biodiesel fuel. Some studies
suggest that the use of biodiesel fuel may produce increases in NOx emissions concurrent with
reductions in other pollutants, promoting the need for additional research and studies.12,13
The diesel fuel referred to as PEMEX fuel in this study is the diesel produced and distributed in
Mexico by Petróleos Mexicanos (PEMEX). In 1938, the president of Mexico nationalized 17
foreign oil companies to create PEMEX, the largest Latin American petroleum company and a
major world exporter of fossil fuel. PEMEX engages in exploration, production, refining,
8
Wikipedia, Ultra-low sulfur diesel, http://en.wikipedia.org/wiki/Ultra_low_sulphur_diesel, accessed 4/4/2007.
New S15 (Ultra Low Sulfur Diesel -ULSD) Regulations,
http://www.chevron.com/products/prodserv/fuels/diesel/ulsd.shtml, accessed 4/4/2007.
10
Clean Diesel Fuel Alliance Information Center, http://www.clean-diesel.org/, accessed 4/4/2007.
11
Heavy-Duty Highway Diesel Program, http://www.epa.gov/otaq/highway-diesel/index.htm, accessed 4/4/2007.
12
Farzaneh, M., J. Zietsman, D. Perkinson, and D. Spillane. School Bus Biodiesel (B20) NOx Emissions Testing.
R08-04/05-TTI-2, Capital Area Council of Governments, Austin, Texas, 2006.
13
Kittleson, et.al. Influence of a Fuel Additive on the Performance and Emissions of a Medimu-Duty Diesel Engine.
SAE 9410015, Society of Automotive Engineers, Warrendal, Pennsylvaina, 1994.
9
24
transportation, storage, distribution, and sales of oil and natural gas.14 The sulfur content of
PEMEX fuel is regulated to be less than 500 ppm. There are some efforts by PEMEX to
introduce diesel fuel with the same standards as ULSD fuel. PEMEX is planning to provide the
ULSD compliant diesel in three phases: first in the U.S.-Mexico border region, then in the
metropolitan areas, and finally in the remainder of Mexico15. It is uncertain exactly when the
ULSD PEMEX fuel will be available in the border region.
To ensure consistency, all diesel used in this study was purchased at the same time and stored in
the test area prior to testing. Complete analyses of the test fuels were performed by Southwest
Research Institute (SwRI) and the results are shown in Appendix C. Table 3 shows a summary of
the specification of the fuels used in this study. The table shows that the fuels were very similar
with the exception of sulfur content and in the case of the B20 fuel, heat of combustion.
Fuel
ULSD
Table 3. Specifications of the Tested Fuels.
Net Heat of
Energy
Sulfur Cetane Aromatics Specific
Combustion Content
(ppm) Index (mass %) Gravity
(btu/lb)
(btu/gal)
9
47.5
26.7
0.8401
18416
129091
Energy Content
Difference From
ULSD (%)
–
B20
8
48.1
NR*
0.8499
17852
126627
1.9
PEMEX
380
50.2
26.9
0.8306
18463
127900
0.9
*NR- Not recorded.
Because biodiesel fuel has lower energy content due to ~11 percent oxygen, the B20 fuel was
expected to result in lower fuel economy. Due to differences in the specific gravity and energy
content, B20 fuel should result in ~2 percent loss in fuel economy, and PEMEX fuel should
result in a 1 percent loss. The research team expects that these changes might be difficult to see
in the data due to the expected variability in the drive cycles.
From previous studies, the emissions differences that are expected from changes in fuel would
include lower PM, CO, and HC for the B20 fuel and possibly higher NOx from the B20 fuel. The
cause of the lower CO, HC, and PM is thought to be due to the oxygen content of the fuel. When
comparing the PEMEX fuel to the ULSD fuel, higher PM is expected from the PEMEX fuel due
to the higher sulfur level of the PEMEX fuel.
It was found during the purging process that the fuel that was circulated through the engine and
fuel system contained black particulate contaminants. It is possible that this black contaminant is
oil contained in the fuel system (it is known that Mexican truck drivers sometimes dispense oil
into the fuel tanks). Figure 17 shows a container on the left with clean fuel and one on the right
with fuel purged from a truck’s fuel system.
14
Answers.com, http://www.answers.com/topic/pemex. accessed 4/4/2007.
Secretariat of the Environment and Natural Resources. ULSF in the Border- Mexico Prospective, http://www.jacccc.org/PDN-ARP/CAAAC/ULSF in the border Mexico perspective.pdf, 2005.
15
25
Figure 17. Fuel Showing Contaminants.
26
3. Results
The dataset assembled in the data handling step can be analyzed using three different measures
of effectiveness.
Distance specific emission rates: describes the emissions rates per unit of distance
traveled (grams per mile [g/mi]). This effectiveness measure is not appropriate for idle
testing because the vehicles are stationary; i.e. the total distance traveled is zero.
Average time specific emissions rates: explains the average emissions rates for a testing
scenario per unit of time such as g/s or grams per hour (g/hr). This value is mostly suitable
for analyzing a single steady-state condition such as steady-state idle testing.
Emissions index: is the exhaust flow weighted average fuel specific emissions rate for a
specific cycle. It describes normalized amount of emissions per unit of fuel consumed by
the vehicle (g/kg fuel). This value is primarily used for comparing different fuels for the
same cycle.
The emissions index was suggested as a useful tool for comparing emissions from different test
configurations (fuels) by the manufacturer of the SEMTEC-DS. It was stated that the emission
index is a more robust measure of effectiveness for on-road emissions testing for comparing
different scenarios.
For this study, the distance specific emissions rate and the emissions index were used for on-road
drive cycle based tests and the time specific emissions rate was used for low- and high-idle
testing. The appropriate effectiveness measures were calculated for each run of the test scenarios.
On-road testing consisted of two cycles representing two different driving patterns — drayage
cycle and long-haul cycles. For each cycle, two tests were performed. The results presented in
this report are the averages of the values from the two runs of each cycle for a specific vehicle
and fuel. Since idling is a steady-state condition, each second of recorded data can be considered
as a repetition; therefore an average over the time of the test provides the mean value of the
effectiveness measure (time specific emission rate [g/hr]).
27
3.1 Idle Tests
Gaseous Emissions Results
The idling data was collected for the 10 trucks using two test modes, low idle (at 600-700 rpm)
and high idle (at about 1200 rpm). Air conditioning was kept off on the drayage trucks (this is
their normal mode of operation) and kept on for the long-haul trucks (provided it was
functioning). If trucks were unable to maintain steady high idle conditions, an operator held his
foot on the pedal, maintaining the higher engine speed. In general, it was found that the
emissions were very similar to U.S. trucks of the same era with very little visible smoke during
idle.16 The procedures used are further discussed in the ―MSAT Sample Collection and Analysis‖
section.
Figure 18 and Figure 19, respectively, illustrate the results of low-and high-idling emissions
testing.
16
Storey, J.M.E., et al. Particulate Matter and Aldehye Emissions From Idling Heavy-Duty Diesel Trucks. SAE
2003-01-0289, Society of Automotive Engineers, Warrendale, Pennsylvania, 2003.
28
Low Idle CO 2 (g/hr)
8000
ULSD
B20
Pemex
6000
4000
2000
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Low Idle CO (g/hr)
80
Long Haul Trucks
ULSD
B20
Pemex
60
40
20
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Low Idle HC (g/hr)
20
Long Haul Trucks
ULSD
B20
Pemex
15
10
5
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Low Idle NOx (g/hr)
200
Long Haul Trucks
ULSD
B20
Pemex
150
100
50
0
1994 1995 1997 1999 2001
Drayage Trucks
1990 1995 1999 2001 2004
Long Haul Trucks
Figure 18. Gaseous Emissions Results for Low-Idling Test at 600 rpm.
29
High Idle CO2 (g/hr)
20000
ULSD
B20
Pemex
15000
10000
5000
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
High Idle CO (g/hr)
200
Long Haul Trucks
ULSD
B20
Pemex
150
100
50
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
High Idle HC (g/hr)
50
Long Haul Trucks
ULSD
B20
Pemex
40
30
20
10
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
High Idle NOx (g/hr)
250
Long Haul Trucks
ULSD
B20
Pemex
200
150
100
50
0
1994 1995 1997 1999 2001
Drayage Trucks
1990 1995 1999 2001 2004
Long Haul Trucks
Figure 19. Gaseous Emissions Results for High-Idling Test at 1200 rpm.
30
These figures show that for the majority of the trucks (8 out of 10) the CO2 emissions rates at
low idle do not show large changes with the different fuels. This is also the case for high idle
CO2 emissions. Although the absolute differences between fuels appear large, they are in the
same general range with differences less than 10 percent. The graphs in Figure 18 and Figure 19
illustrate that while idling the drayage trucks’ CO2 emissions are almost the same (at low idle) or
have no apparent correlation with truck age. However, it appears that for the long-haul trucks the
CO2 emissions rate is noticeably higher for trucks newer than 1999 than the older long-haul
trucks (35 percent-to-100 percent higher). A potential explanation for this result could be the fact
that the air conditioning units of long-haul trucks the model years 1995 and 1990 were not
operational, while the air conditioning was working on the newer long-haul trucks during the
tests. Low idle results show the same trend in general, although it seems that the impact of the
working air conditioning on low idle CO2 emissions is much smaller than for high idle (10
percent-to-40 percent higher CO2 for trucks with working air conditioning than those without a
working air conditioner).
Figures 18 and 19 also show the CO emissions results for drayage trucks. The B20 fuel shows a
decreasing (compared to the ULSD fuel) effect on the CO emissions rate at both idling tests (up
to 40 percent lower for both low and high idling). The PEMEX fuel shows the same trend with
up to 40 percent reduction for low idling and up to 35 percent reduction for high idling. The
long-haul trucks do not show a clear pattern of fuel impact on the CO emissions rates during
idling. Some trucks show an increase in the CO rate for a certain fuel and the others show no
difference or a decrease for the same fuel. Furthermore, the graphs show that a newer engine
does not appear to have a positive impact on CO emissions rates during idling as would be
expect. The results also are inconclusive about the impact of air conditioning on CO emissions
during idling. In general, the long-haul trucks tested had higher CO emissions rates than the
drayage trucks.
For the majority of trucks, the B20 fuel has caused 40 percent-to-10 percent reductions
(compared to ULSD fuel) in hydrocarbon (HC) emissions rates. The PEMEX fuel shows the
same trend (six trucks showed reductions) at idling conditions, with reductions of 30 percent-to10 percent for high idling and 33 percent-to-5 percent for low idling. Surprisingly, the results
suggest that the age is inversely related to HC emissions during idling. The highest emissions
rates belong to the newer vehicles and the older vehicles are producing less HC per unit of time.
This is possibly due to the higher fuel injection pressures of the newer trucks resulting in finer
fuel spray and lower PM, but higher HC due to unburned fuel escaping the combustion chamber
more easily under idle conditions.
With the exception of three trucks, the B20 fuel shows a slightly decreasing effect on NOx
emissions rates at both low and high idling conditions when compared to the ULSD fuel. In
general, there was a 2 percent-to-9 percent reduction at low idle and 1 percent-to-15 percent
reduction at high idle. The PEMEX fuel and B20 fuel also appear to have similar impact on NOx
emissions during idling; with 0.4 percent-to-19 percent reductions at low idle and 2.6 percent-to15 percent reductions at high idle. The engine age does not show an apparent impact on the NOx
emissions rates during idling. For example, the 2004 truck had almost the same or higher NOx
rate than the 1990 truck. The exhaust gas recirculation (EGR) system of the 2004 truck was
either malfunctioning or not installed.
31
In general, the gaseous emissions during idle suggest that at idling mode, the ULSD fuel does not
show an emissions benefit over the tested PEMEX fuel (sulfur content of 380 ppm) for the tested
fleet. It should be noted that the PEMEX fuel used has a higher cetane index as compared with
the ULSD fuel (50.2 versus 47.5). Previous studies have shown that higher cetane numbers can
increase NOx slightly and reduce CO and HC. All else being equal, higher cetane tends to
advance the ignition timing which causes a decrease these emissions and a slight increase in
NOx. The increase in NOx would be most obvious on the driving cycles where the engine is
under load.
The B20 fuel shows a reduction in CO, HC, and NOx emissions during idling. The B20 fuel has
no impact on CO2 rate, however, assuming the same energy content as the ULSD fuel, 20
percent of the CO2 from the B20 fuel is coming from a renewable source, which can be
considered a reduction. Air conditioning usage shows some impact on CO2 and NOx, although, it
does not show any noticeable effect on CO and HC.
32
PM Emissions Results
MSAT emissions, including formaldehyde, acetaldehyde, and diesel PM, were measured during
the idle tests only due to the requirement for dilution sampling.
The diesel PM emissions tended to decrease with age, especially when viewed in combination
with previously obtained data on nine older drayage trucks in El Paso.17 It may also be observed
that the emissions rate for PM is considerably below the EPA guidance for extended truck idling
emissions of 3.68 g/hr.18 (See Figure 20). The figure shows that emissions generally decrease
with truck age, with some exceptions.
2.5
PM Emissions (g/hr)
2
1.5
1
0.5
0
1985 1987 1989 1990 1992 1994 1994 1995 1995 1996 1996 1997 1997 1998 1999 1999 2001 2001 2004
Truck year
Figure 20. PM Emissions from Mexican Trucks.
When fuel effects are examined, the influence of each fuel is less easy to be discerned. Figure 21
shows the emissions of the Laredo trucks as a function of fuel for both low-and high-idle rates.
For the low-speed idle, emissions decrease with the B20 fuel use and increase with the PEMEX
17
Zietsman, J., J.C. Villa, T.L. Forrest, and J.M. Storey. Mexican Truck Idling Emissions at the El Paso - Ciudad
Juarez Border Location. Southwest Region University Transportation Center, The Texas A&M University System,
College Station, Texas, 2005.
18
Guidance for Quantifying and Using Long Duration Truck Idling Emissions Reductions in State Implementation
Plans and Transportation Conformity. EPA420-B-04-001, U. S. Environmental Protection Agency, Washington,
D.C., 2004.
33
fuel, but the trend is opposite for the high-speed idle case. In previous studies of biodiesel fuel
blends, several groups have seen overall PM reduction compared with the base fuels. The higher
cetane number of the PEMEX fuel may contribute to its relatively neutral effect on PM
emissions, despite its higher sulfur level.
2.5
Low-Idle
PM emissions (mg/hr)
ULSD
B20
Pemex
2
Long Haul Trucks
1.5
Drayage Trucks
1
0.5
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
5
PM emissions (mg/hr)
High-Idle
ULSD
4
B20
Pemex
3
Drayage Trucks
Long Haul Trucks
2
1
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Figure 21. Diesel PM Emissions for the Laredo trucks.
34
Table 4 illustrates the average values for the PM emissions. For the drayage trucks, biodiesel fuel
reduces PM under both low-and high-idle conditions. However, for the long-haul trucks,
biodiesel fuel results in the highest PM emissions. High-idle conditions tend to favor the
formation of soluble organic fraction (SOF), because the engine is operating at higher speed with
low or no load, and unburned fuel and lube can be entrained into the exhaust and become part of
the PM that is measured by the filter. In the same engine, biodiesel fuel, which consists of just a
few fairly high boiling components, tends to have higher SOF than regular diesel fuel. Thus, the
fraction of the PM that is solid may well be lower with the B20 fuel, even though the measured
PM, including the SOF is higher. Although time and budget did not allow for SOF extraction on
the filters, ORNL preserved the sample filters and is measuring the PM-SOF under a different
DOE-funded task and will share the results as soon as they become available.
Table 4. PM Emissions Results (mg/hr).
Idle speed
ULSD
B20
PEMEX
Low
0.43
0.33
0.49
High
1.48
1.31
1.37
Low
0.59
0.90
0.44
High
1.80
2.15
1.69
Low
0.51
0.62
0.47
High
1.64
1.73
1.53
Drayage
Long-haul
All Trucks
MSAT Analysis
In addition to PM, measurements were made of formaldehyde and acetaldehyde in the diluted
exhaust. One truck in particular, Drayage Truck 1, a 1999 model, had much higher aldehyde
emissions than all of the other trucks. This trend was consistent across separate measurements of
fuels and engine speeds. This truck also showed evidence of a fuel pump problem after changing
the fuel system to the test fuel, resulting in the eventual replacement of the fuel pump. Figure 22
shows the formaldehyde and acetaldehyde data with the high-emitting truck and Figure 23 shows
the same data without it to facilitate comparisons.
The aldehydes are products of incomplete combustion, so they are generally higher at idle than
under load. With exception of the 1999 drayage truck, the emissions of formaldehyde and
acetaldehyde were low compared with earlier work at El Paso19 and idling U.S. trucks.20
19
Zietsman, J., J.C. Villa, T.L. Forrest, and J.M. Storey. Mexican Truck Idling Emissions at the El Paso - Ciudad
Juarez Border Location. Southwest Region University Transportation Center, The Texas A&M University System,
College Station, Texas, 2005.
20
Storey, J.M.E., et al. Particulate Matter and Aldehye Emissions From Idling Heavy-Duty Diesel Trucks. SAE
2003-01-0289, Society of Automotive Engineers, Warrendale, Pennsylvania, 2003.
35
3000
Formaldehyde emissions (mg/hr)
ULSD
B20
PEMEX
2000
Low-speed idle
High-speed idle
1000
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
0
3000
Acetaldehyde emissions (mg/hr)
ULSD
B20
PEMEX
2000
1000
Low-speed idle
High-speed idle
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
0
Figure 22. Formaldehyde and Acetaldehyde Emissions for all 10 Laredo Trucks.
(Including Higher-Emitting Drayage Truck 1, a 1999 Model.)
36
20
04
Low-speed idle
20
01
Low-speed idle
19
99
B20
19
95
ULSD
19
94
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
B20
20
01
19
90
19
94
19
95
19
95
19
97
19
99
19
99
20
01
20
01
20
04
ULSD
19
99
19
97
19
95
19
90
Acetaldehyde emissions (mg/hr)
Formaldehyde emissions (mg/hr)
800
PEMEX
600
High-speed idle
400
200
0
800
PEMEX
600
400
High-speed idle
200
0
Figure 23. Formaldehyde and Acetaldehyde Emissions by Model Year.
37
Discussion of Idling Emissions Results
Results from these studies did not confirm some of the study team’s original expectations of the
study design. There was an expectation that the change to the ULSD and B20 fuels would result
in significantly lower emissions, especially when compared to the PEMEX fuel. Earlier studies
have often shown an increase in NOx with biodiesel fuel usage. The idling results obtained in
this study showed very little change. Similarly, for the MSATs, the expectation was that the
―cleaner‖ ULSD fuel would have lower emissions than the PEMEX fuel. With the exception of
the 1999 truck identified earlier, trucks operating on the three test fuels, were cleaner than the
Mexican trucks tested in El Paso and the U.S. trucks tested in Aberdeen. The lack of difference
may be lost in the relatively low levels of emissions. Overall, one reason for the lower emissions
among the Laredo trucks could be the higher level of maintenance observed with these trucks as
opposed to the El Paso trucks.
Another potential rationale for the difference is the higher cetane index of the fuels. Higher
cetane will result in a more efficient burn, especially at idle, leading to lower emissions of partial
combustion products such as the aldehydes. The Pemex fuel has a very comparable cetane index
to the U.S. ULSD fuel (see Table 3). Because Mexico is planning to adopt the U.S. fuel standard,
at least in the border states, refinery processes are likely to become more similar, leading to
higher cetane fuels than would have been encountered in El Paso during the previous year or in
Aberdeen in 2002. Before the ULSD fuel regulations, average cetane index for on-road diesel
was 42-45 and it was expected that the El Paso fuel would have similar or lower cetane index
values.21 Furthermore, no clear trend was observed for the B20 fuel in terms of aldehyde
emissions. It was expected that the methyl ester would be a good candidate for increased
formaldehyde or acetaldehyde emissions, but that increase was not observed.
21
Owen, K. and T. Coley. Automotive Fuels Reference Book, 2nd Edition. Society of Automotive Engineers,
Warrendale, Pennsylvania, p.391.
38
3.2 On-Road Tests
The results of on-road emissions testing are provided in the following figures. Figure 24 shows
the emissions index and the distance specific emissions rates for the drayage cycle testing while
Figure 25 provides the results for long-haul drive cycle testing. These results are also shown in
Appendix B in a tabular format. In Figure 24 and Figure 25, the graphs on the left side show the
emissions indices and the right side presents the distance specific emissions rates. The main
effectiveness measures are the distance specific emissions rate and emissions indices are only
used for verification purpose. The calculation of emissions index uses the molecular weight of
the pollutant. The particulate matter, which includes many different molecules, does not have a
unique molecular weight and, therefore, an emission index for PM can, therefore, not be
calculated. In addition, the on-road PM is derived from the CATI instrument, which uses light
scattering to determine PM concentration based on calibration with limited engines.
Gaseous Emissions Results
The emissions index for CO2 is based on the fuel flow derived from CO2 emissions, so the CO2
emissions index graph shows the excellent consistency of the CO2 measurement between fuels
and different trucks. This consistency shows that leaks were not an issue, and the instrument was
stable throughout the two-week experiment. However, there are differences in distance specific
emissions rates among the fuels for long-haul trucks due to the differing efficiencies of the truck
engines. Therefore, if more fuel is burned to cover the driving cycle, the mass of CO2 per mile
increases. From the fuels analysis, the B20 fuel has about 2.5 percent less carbon by weight than
the other fuels – this difference would translate into lower miles/gallon, but not CO2/mile.
The consistency between fuels for a given truck, though, shows the relative consistency of the
driving cycles for that truck. On average, the trucks showed excellent consistency on the driving
cycle, with the exception of the 1995 and 1999 long-haul trucks, which had 15 percent-to-20
percent differences in the CO2 emissions rates between fuels. The CO2 graphs also suggest that
air conditioning usage has an obvious impact on the CO2 emissions from the moving trucks.
Trucks with working air conditioning (1990 and 1995 model long-haul trucks) have higher
average CO2 emissions per unit of length (g/mi). The impact of air conditioning seems to be
greater for the long-haul cycle than for the drayage cycle. This difference may be the result of
having more stop-and-go driving with hard accelerations under drayage driving conditions, as
opposed to long-haul driving that is characterized by few stops.
With exception of two trucks for each cycle, the B20 fuel appears to reduce the average CO
emissions (from the ULSD fuel), notably a 14 percent-to-37 percent reduction in distance
specific rates for drayage cycle and a 4 percent-to-34 percent reduction for long-haul cycle. For
the majority of the trucks, CO emissions rates associated with the B20 fuel are the lowest among
the fuels. The PEMEX fuel also shows the same pattern; with a 5 percent-to-36 percent reduction
in distance specific rates for drayage cycle and a 3 percent-to-47 percent reduction for the longhaul cycle. Although a CO reduction was expected with the B20 fuel, it is not clear why the
PEMEX fuel has this effect on CO emissions. Age does not show an obvious effect on long-haul
trucks’ CO emissions for either cycle. For the drayage trucks the two newest models have
substantially lower CO rates (g/mi) than the older ones. A comparison of the CO rates between
drayage and long-haul trucks suggests that on average long-haul trucks have lower CO
39
emissions. This may be the result of better maintenance on long-haul trucks. Furthermore, there
is no obvious correlation between air conditioning usage and changes in CO rates.
HC emissions results show trends similar to those for idling HC emissions. The B20 and
PEMEX fuels appear to cause substantial reductions in the HC emissions (from the ULSD fuel).
As was the case for CO, the B20 fuel appears to have the lowest emissions rate compared to the
other two fuels. Truck age seems to be inversely related to HC emissions rates with newer trucks
having higher HC emissions rates than the older ones.
In contrast to the idle test results, the B20 fuel appears to increase NOx emissions; with 1
percent-to-16.3 percent increases (from the ULSD fuel) for the drayage cycle and 1 percent-to-14
percent increases for the long-haul cycle. The PEMEX fuel also shows the same trend as the B20
fuel, with a slightly lower increase in the NOx emissions rates. Vehicle age does not appear to
have an effect on the NOx emissions from either drayage or long-haul cycles. Air conditioning
usage also does not show a correlation with changes in NOx emissions rates. The NOx rates for
the long-haul cycle are slightly higher than the rate for the drayage cycle, which has substantial
idling periods. Note that the results for the 2004 long-haul truck show no change from earlier
trucks.
PM Emissions Results
The distance specific PM results presented in Figure 24 and Figure 25 illustrate that for all the
trucks, the B20 fuel substantially reduces PM emissions as measured by the CATI device. The
reductions are between 13 percent-to-48 percent (from the ULSD fuel) for the drayage cycle and
15 percent-to-37 percent for the long-haul cycle. The PEMEX fuel shows a reduction in PM
emissions rate for the majority of the trucks; although the reductions are smaller than for the B20
fuel. The reductions of PM resulting from the PEMEX fuel are in the range of 1 percent-to-36
percent for the drayage cycle and 3 percent-to-27 percent for the long-haul cycle. For both
groups of trucks, the oldest trucks, which fall into pre-1995 category, have the highest PM rates.
Post-1995 trucks show mixed results regarding the impact of truck age on PM emissions. This
trend is mostly attributed to the fact that the EPA-set PM standards for diesel engines changed
for engines manufactured in 1994 and after from 0.25 g/bhp.hr for pre-1994 engines to 0.1
g/bhp.hr for post-1994 engines. This standard remained unchanged until recently when the new
PM level standard was set at 0.01 g/bhp.hr for engines manufactured in 2007 and after. Table 1
shows time line of EPA emissions standards for diesel engines manufactured before 2007. Air
conditioning usage does not have an apparent impact on PM emissions from the tested trucks.
The changes observed in PM emissions with the PEMEX fuel may be the result of fuel system
cleanliness. The order of fuel types tested was the ULSD fuel, followed by the B20 fuel, and the
PEMEX fuel. The disturbance and substitution of fuels described in the experimental section
may have resulted in the loosening and removal of deposits from the fuel system. Biodiesel fuel,
in particular, has a detergent effect. Thus, the emissions may be decreasing because the fuel
injection is behaving more similarly to original specifications. Another factor in the
improvement of the PEMEX fuel may be the increased cetane index, which in general, will
improve emissions.
40
ULSD
B20
4000
Pemex
3000
CO2 (g/mi)
CO2 (g/kg fuel)
4000
2000
1000
0
1990 1995 1999 2001 2004
Drayage Trucks
40
ULSD
1994 1995 1997 1999 2001
Long Haul Trucks
B20
1990 1995 1999 2001 2004
Drayage Trucks
40
Pemex
Long Haul Trucks
ULSD
B20
Pemex
30
30
CO (g/mi)
CO (g/kg fuel)
Pemex
1000
1994 1995 1997 1999 2001
20
20
10
10
0
0
1994 1995 1997 1999 2001
5
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Long Haul Trucks
ULSD
B20
1990 1995 1999 2001 2004
Drayage Trucks
4
Pemex
4
Long Haul Trucks
ULSD
B20
Pemex
3
HC (g/mi)
HC (g/kg fuel)
B20
2000
0
3
2
2
1
1
0
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
60
1994 1995 1997 1999 2001
Long Haul Trucks
ULSD
B20
1990 1995 1999 2001 2004
Drayage Trucks
50
Pemex
50
Long Haul Trucks
ULSD
B20
Pemex
NOx (g/mi)
40
40
30
20
30
20
10
10
0
0
1994 1995 1997 1999 2001
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Long Haul Trucks
Drayage Trucks
1990 1995 1999 2001 2004
Long Haul Trucks
1000
ULSD
PM (mg/mi)
NOx (g/kg fuel)
ULSD
3000
B20
Pemex
750
500
250
0
1994
1995
1997
1999
Drayage Trucks
2001
1990
1995
1999
2001
2004
Long Haul Trucks
Figure 24. Drayage Cycle — Emissions Rates and Emissions Index.
41
ULSD
B20
4000
Pemex
3000
CO2 (g/mi)
CO2 (g/kg fuel)
4000
2000
2000
0
1990 1995 1999 2001 2004
Drayage Trucks
40
ULSD
1994 1995 1997 1999 2001
Long Haul Trucks
B20
1990 1995 1999 2001 2004
Drayage Trucks
30
Pemex
ULSD
Long Haul Trucks
B20
Pemex
30
CO (g/mi)
CO (g/kg fuel)
Pemex
1000
1000
1994 1995 1997 1999 2001
20
20
10
10
0
0
1994 1995 1997 1999 2001
3
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
Long Haul Trucks
ULSD
B20
1990 1995 1999 2001 2004
Drayage Trucks
3
Pemex
2
HC (g/mi)
HC (g/kg fuel)
B20
3000
0
1
0
Long Haul Trucks
ULSD
B20
Pemex
2
1
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
60
1994 1995 1997 1999 2001
Long Haul Trucks
ULSD
B20
1990 1995 1999 2001 2004
Drayage Trucks
40
Pemex
Long Haul Trucks
ULSD
B20
Pemex
50
NOx (g/mi)
NOx (g/kg fuel)
ULSD
40
30
20
30
20
10
10
0
0
1994 1995 1997 1999 2001
1990 1995 1999 2001 2004
Drayage Trucks
1994 1995 1997 1999 2001
Long Haul Trucks
PM (mg/mi)
1000
Drayage Trucks
ULSD
B20
1990 1995 1999 2001 2004
Long Haul Trucks
Pemex
750
500
250
0
1994 1995 1997 1999 2001
Drayage Trucks
1990 1995 1999 2001 2004
Long Haul Trucks
Figure 25. Long-Haul Cycle — Emissions Rates and Emissions Index.
42
4. Conclusions
Potential for Trucking beyond the U.S. Commercial Zone
Through an examination of Mexican and U.S. trucking practices and a series of interviews with
Mexican trucking interests the study team found that most Mexican long-haul carriers do not
currently cross their trucks into the U.S. commercial zone and would be reluctant to change that
aspect of their operations. Many Mexican drayage firms currently crossing the border do not
intend on pursuing contracts beyond the U.S. commercial zone, even if such movements are
permitted.
Emissions Testing
Test Protocol
The study team tested five drayage and five long-haul trucks, all currently operating in Mexico.
The tested trucks ranged from model year 1990 to 2004 with engine displacements ranging from
10.8 to 14.0 liters. All the tested trucks were subject to two idling (low and high) and two onroad (drayage and long-haul cycles) tests for three different fuels — ULSD (base fuel), biodiesel
mix (B20), and PEMEX diesel. Several emissions measurement devices including two portable
emissions measurement units, a filter system, and a TEOM unit were used to measure different
pollutants and toxics from the trucks in different modes of operation. The measured pollutants
were PM, NOx, HC, CO, and CO2. Additionally, two mobile source toxics, formaldehyde and
acetaldehyde, were also measured. The toxics were measured only for the idle mode, while the
pollutants were tested for all the operation modes.
NOx Emissions
It was found that for idling modes (low and high) the B20 and PEMEX fuels tend to decrease
NOx emissions slightly (compared to the ULSD fuel). For on-road modes (drayage and longhaul cycles), both the B20 and PEMEX fuels seemed to increase NOx. There was no clear
correlation between vehicle age and NOx emissions rates. The impact of air conditioner usage on
NOx was mixed; with a notable impact in idle mode and no apparent effect for on-road tests.
HC Emissions
Both the B20 and PEMEX fuels reduced hydrocarbons emissions during all modes of operation
when compared to the ULSD fuel with the B20 fuel having the highest reduction. The age of the
trucks appeared to have an inverse effect (newer trucks showed higher emissions) on HC
emissions, which might be the result of finer fuel injection in newer diesel engines. The effect of
air conditioning usage on HC was not clear because of the mentioned inverse impact of age on
HC.
43
CO Emissions
Similar to HC emissions, the B20 and PEMEX fuels tended to decrease CO emissions compared
to the ULSD fuel for all operation modes. It was found having a newer engine does not appear to
have a positive impact on CO emissions rates in the idling mode as would be expected. The
results were mixed for on-road tests: no age impact was observed for long-haul trucks. Newer
drayage trucks had lower CO emissions than the older ones. There was no obvious correlation
between air conditioning usage and changes in CO rates.
CO2 Emissions
The results showed that the fuel type does not have an impact on the CO2 emissions. However, it
must be noted that 20 percent of the B20 fuel came from a renewable source. CO2 from this
portion can be considered as an emission benefit. Air conditioning appeared to have a notable
impact on CO2 emissions. The age of the trucks showed no apparent effect on CO2 emissions.
PM Emissions
The B20 fuel appeared to substantially reduce PM emissions (from the ULSD fuel) for the onroad operational mode. The PEMEX fuel also seemed to reduce PM, but to a lesser extent. The
PEMEX fuel used had a higher cetane index as compared with the ULSD fuel (50.2 versus 47.5).
Previous studies have shown that higher cetane numbers can increase NOx slightly and reduce
CO and HC. All else equal, higher cetane tends to advance the ignition timing which causes a
decrease these emissions and a slight increase in NOx. The increase in NOx would be most
obvious on the driving cycles where the engine is under load. Additionally, the process to lower
the sulfur to develop the ULSD fuel could involve the addition of hydrogen that might result in
higher PM numbers. There is also a potential lubricity effect (contaminants in the fuel system
mixes into the fuel line) resulting in higher than expected emissions rates, especially for PM.
Pre-1995 trucks were found to have the highest on-road PM emissions rate, while the impact of
the vehicles’ age on PM for post-1995 trucks was not clear. Air conditioning usage did not show
a clear impact on on-road PM emissions.
In addition, with the exception of one vehicle, PM emissions were significantly lower in this
study than those observed for the drayage trucks in El Paso. Significant differences included:
more older vehicles in the El Paso study;
no fuel purge/fuel changes; and
fuel that may have been of lower quality.
Mobile Source Air Toxics
The formaldehyde and acetaldehyde emissions were significantly lower than observed previously
in idling trucks from the U.S. and Mexico. The higher cetane index of all three fuels may be
responsible for this observed reduction. No additional aldehyde emissions were detected from
the biodiesel fuel, despite its fuel oxygen. Because the new ultralow sulfur rules have improved
fuel quality in both the U.S. and Mexico, there is no reason to expect that ULSD or B20 fuels
would have a noticeable effect on the aldehyde MSAT emissions.
44
In general, the results of this study suggest that using the ULSD fuel instead of the PEMEX fuel
might not provide the expected emissions benefit. The results showed that for the tested fleet, the
ULSD fuel reduces NOx emissions as compared to the PEMEX fuel. On the other hand, the
ULSD fuel appeared to increase the CO, HC, and PM emissions in both drayage and long-haul
driving modes. In interpretation of these results, note that the introduction of the ULSD fuel has
been intended to serve as a technology enabler to pave the way for the advanced sulfur-sensitive
exhaust emissions control devices. In this context, it is the combination of the model year 2007
diesel engines, equipped with advanced emissions control devices, and the lower sulfur diesel
fuel that the EPA expects to result in reduced emissions to the atmosphere.
Possible Explanations for Lower Emissions of PEMEX in Some Instances
It should be noted that the PEMEX fuel used had a higher cetane index as compared with
ULSD (50.2 versus 47.5). Previous studies have shown that higher cetane numbers can
increase NOx slightly and reduce CO and HC. All else being equal, higher cetane tends
to advance the ignition timing which causes a decrease these emissions and a slight
increase in NOx. The increase in NOx would be most obvious on the driving cycles
where the engine is under load.
The process to lower the sulfur to develop ULSD could involve the addition of hydrogen
that might result in higher PM numbers.
There is a potential lubricity effect (contaminants in the fuel system mixes into the fuel
line) resulting in higher than expected emissions rates, especially for PM.
When a new fuel is introduced the timing and performance of the vehicle can be changed
slightly, potentially affecting emissions.
Final Observations
Biodiesel (B20) clearly produced the best results with reductions in CO, PM, and HC emissions.
There was no effect on CO2 emissions and the results for NOx were mixed with slight decreases
during idling and slight increases during driving.
45
46
5. Recommendations
The results of the study can be refined and then combined with the fleet characteristics to provide
a macroscopic emissions model to calculate the total emissions from trucks crossing the U.S.Mexico border. By incorporating data from other border crossings, the model can be used to
estimate emissions at all Texas border crossings. Such a model will be easy to apply and has the
flexibility to consider the impact of different effects such as seasonal variation, daily variations,
hourly variations, and even the impact of emissions control strategies.
At a more detailed level, the emissions data collected in this study also provides an opportunity
to develop a series of instantaneous emissions models. The flexibility of an instantaneous model
enables researchers to investigate the impact of different border crossings and different border
crossing systems on emissions. The development of such a model requires data from different
sources (emissions rates from this study and other studies, GPS-collected vehicle speed, road
profile, vehicle location, and engine speed) to be combined and analyzed according an existing
framework (e.g. VT-Micro or EPA’s MOVES).
A more comprehensive study of this nature would involve a larger sample size of trucks and a
fuel conditioning period. There is also some uncertainty about the actual fuel being used in
Mexico. It would be useful to develop a better understanding of fuel types used at different
locations in Mexico and to test the emissions impact of these fuels.
In addition to fuel types, there is a real need to understand the emissions impact of using various
retrofits and emissions reduction devices. The technologies identified under the SmartWay
program need to be tested during actual operating conditions.
48
6. Acknowledgements
The study team would like to acknowledge the following individuals without whom this project
would not have been possible:
Jim Yarbrough of the EPA Region 6 for his guidance and support.
Mario Salinas of Texas Department of Public Safety for making their facilities available
for our testing and assisting with obtaining approval to test Mexican trucks in the U.S.
Danny Magee of Texas Department of Transportation for allowing us to us the Toll Road
for testing and supporting us during the study.
Brian Beckman and Jeremy Dabbeekeh of Clean Air Technologies for operating the
Montana CATI unit during the study and converting the CATI PM data.
Edward Brackin of TTI for assisting with the PEMS data collection and fuel purging
A.J. Rand of TTI for assisting with the PEMS data collection and fuel purging
Lisa Nimocks of TTI for assisting with all the logistics for the study.
Miguel Angel Alceda of SET Logistics for providing assistance in securing Mexican
tractors and trailer to carry out the tests.
Jorge de la Concha of SET Logistics for providing invaluable assistance in coordinating
with Mexican drayage and long-haul trucking companies and securing driver availability
throughout the field tests.
Noberto Domingo and Mike Kass of Oak Ridge Nation Laboratory for assisting with the
PM and MSAT data collection.
Tara Ramani of TTI for assisting with the writing of this report.
50
APPENDIX A
53
Proportion
80%
70%
US Trucks (2003 UC Davis survey)
60%
Mexican trucks (2006 TTI survey)
50%
40%
30%
20%
10%
0%
0-2
3-4
5-6
7-8
9 - 10
> 10
Tractor age (yr)
Figure A. 1. U.S. and Mexican Truck Age Frequency (UC Davis Survey 2003 and TTI
Survey 2006)
54
Average diesel price ($/gal)
3.5
3
2.5
2
1.5
Border region - US Side
Border region - Mexican Side
1
Laredo, TX
0.5
0
Jan.
2006
Feb.
2006
Mar.
2006
Apr.
2006
May
2006
Jun.
2006
Jul.
2006
Aug.
2006
Sep.
2006
Oct.
2006
Nov.
2006
Figure A. 2. Comparative average diesel price at US-Mexico border region
55
APPENDIX B
57
Table B. 1. Gaseous Emissions Rates for Low Idling at 600 rpm.
CO2 (g/hr)
1994
4320
3960
3816
Drayage Trucks
1995
1997
1999
4572
4392
5076
4248
4392
4716
4392
4140
4392
2001
4860
3816
4716
Long-haul Trucks
1995
1999
2001
5904
4860
5652
4464
4932
5544
5580
4752
5184
2004
5004
5544
5184
1994
34.2
19.08
21.96
1995
29.16
22.32
24.12
1997
25.56
20.16
20.52
1999
26.40384
28.05408
24.25853
CO (g/hr)
2001
1990
27.36 ULSD 43.56
13.32
24.12
B20
23.04 PEMEX
27
1995
53.64
54
53.64
1999
21.6
33.48
26.28
2001
35.28
37.8
33.48
2004
46.44
52.2
39.6
1994
92.88
87.12
86.4
1995
109.44
140.4
132.48
1997
90
87.84
80.28
1999
81.72
76.68
75.96
NOx (g/hr)
2001
1990
96.48 ULSD 96.48
87.48
90
B20
95.4 PEMEX 96.12
1995
176.04
118.8
157.68
1999
111.96
106.92
103.68
2001
131.4
183.24
106.56
2004
79.56
93.96
95.76
1995
9.72
14.76
8.28
1999
8.64
7.2
8.28
2001
13.68
14.4
15.12
2004
11.88
13.68
7.92
ULSD
B20
PEMEX
1990
4428
3960
4032
HC (g/hr)
1994
5.4
2.88
3.96
1995
3.96
3.6
3.6
1997
7.56
6.12
7.92
1999
12.6
11.52
12.6
2001
13.68 ULSD
9.36
B20
14.76 PEMEX
1990
8.64
6.12
7.56
59
Table B. 2. Gaseous Emissions Rates for High Idling at 1200 rpm.
CO2 (g/hr)
1994
9828
11124
9180
Drayage Trucks
1995
1997
1999
9036
12384
9252
8100
12204
9540
8460
11772
8352
2001
11448 ULSD
10152
B20
11340 PEMEX
1990
9252
7452
7632
Long-haul Trucks
1995
1999
2001
8928
12204 13536
7920
12924 14940
7812
12564 14832
2004
14652
14220
15876
CO (g/hr)
1994
119.52
95.4
84.6
1995
88.2
66.24
72.36
1997
96.12
75.6
73.8
1999
99.72
96.84
60.48
2001
89.64
53.28
77.4
1990
ULSD 151.56
85.68
B20
PEMEX 79.56
1994
188.28
203.4
163.8
1995
209.88
197.28
191.52
1997
160.2
153
147.6
1999
123.12
121.32
111.6
NOx (g/hr)
2001
150.48 ULSD
141.48
B20
146.52 PEMEX
1994
15.84
12.96
13.32
1995
12.96
11.52
14.76
1997
29.88
23.04
26.28
1999
38.88
32.4
34.92
2001
42.12
34.56
41.04
1995
119.88
146.52
108.72
1999
70.56
113.04
98.64
2001
112.68
104.4
128.16
2004
122.76
126.72
121.32
1990
154.8
133.92
144
1995
214.56
165.96
180.72
1999
198.72
208.44
206.64
2001
198
212.76
186.48
2004
196.92
187.2
200.16
1990
30.24
17.64
18.72
1995
19.08
25.92
17.28
1999
27
23.04
25.56
2001
39.24
38.88
46.08
2004
27.72
27.72
22.32
HC (g/hr)
60
ULSD
B20
PEMEX
Table B. 3. Average Emissions Index for Drayage Drive Cycle.
CO2 (g/kg fuel)
Drayage Trucks
Long-haul Trucks
1994
1995
1997
1999
2001
1990
1995
1999
2001
2004
3007.8 3033.95 2994.85 2915.35 2797.5 ULSD
2763
2989.5 2943.9 2996.35 2918.8
2988.85 3038.4 2991.8 3057.4 2855.85 B20
2869.5 2876.9
2960 3039.85 2970.05
3014.65 3156.9 2976.55 2928.35 2869.65 PEMEX 2822.1 2903.25 3103
3011.9 2870.05
1994
25.3
21.66
23.82
1995
29.4
22.38
24.33
1997
36.84
22.92
32.22
1999
15.61
12.44
13.26
CO (g/kg fuel)
2001
1990
7.43
12.83
ULSD
7.59
10.78
B20
8.46 PEMEX 11.09
1995
25.51
19.47
20.61
1999
11.43
8.09
9.31
2001
7.38
7.92
7.94
2004
15.45
11.82
12.07
1994
30.69
30.82
30.63
1995
34.98
43.38
41.51
1997
32.29
32.02
31.18
1999
24.54
27.02
25.26
NOx (g/kg fuel)
2001
1990
26.3
27.24
ULSD
30.18
28.76
B20
26.05 PEMEX 27.36
1995
50.36
50.97
51.11
1999
26.78
28.56
30.58
2001
24.34
25.19
23.75
2004
21.34
23.16
22.03
1999
3.97
2.21
3.07
HC (g/kg fuel)
2001
1990
3.33
2.39
ULSD
2.84
1.37
B20
3.82 PEMEX 2.03
1995
1.49
2.3
1.34
1999
2.81
1.97
3.09
2001
3.2
2.58
3.3
2004
2.87
2.41
1.76
1994
1.48
0.8
1.41
1995
1.72
1.88
2.14
1997
3.54
2.64
2.24
61
Table B. 4. Average Distance-Specific Emissions Rates for Drayage Drive Cycle.
CO2 (g/mi)
Drayage Trucks
Long-haul Trucks
1994
1995
1997
1999
2001
1990
1995
1999
2001
2004
2892.09 2989.1 3030.28 2786.99 2834.82 ULSD 3131.25 3057.36 2891.42 3630.35 3358.33
2786.31 2797.73 3045.07 2961.4 2665.82 B20 3261.14 2500.11 3126.99 3642.48 3505.48
2945.23 2906.85 2948.1 2798.58 2858.44 PEMEX 2962.97 2556.65 3541.4 3867.39 3403.21
CO (g/mi)
1994
26.52
22.88
25.5
1995
32.88
22.71
24.68
1997
37.64
25.83
35.56
1999
13.36
10.45
10.98
2001
5.16
4.54
5.84
1994
23.11
22.68
23.56
1995
30.21
32.88
31.47
1997
28.81
29.21
27.04
1999
19.34
22.02
20.08
2001
23.33
24.99
22.71
1994
0.79
0.39
0.72
1995
0.88
1.15
1.26
1997
2.12
1.54
1.32
1999
2.04
1.22
1.75
2001
2.11
1.42
2.34
1994
767.13
564.44
645.26
1995
484.85
422.5
447.84
1997
594.93
430.25
508.8
1999
362.79
308.74
322.72
ULSD
B20
PEMEX
1990
14.63
11.25
9.89
1995
25.73
20.11
21.44
1999
9.32
7.93
9.17
2001
6.72
6.92
7.58
2004
14.88
12.58
13.34
1990
24.48
25.84
22.9
1995
45.5
37.95
38.47
1999
21.09
24.53
28.08
2001
25.62
26.37
26.58
2004
21.47
24.26
22.75
1990
1.81
0.92
1.33
1995
0.9
1.27
0.66
1999
1.57
1.33
2.36
2001
2.58
2.04
3
2004
2.06
1.9
1.3
1995
362.64
292.27
247.48
1999
346.87
288.81
414.5
2001
582.04
298.31
573.78
2004
530.8
445.84
395.15
NOx (g/mi)
ULSD
B20
PEMEX
HC (g/mi)
62
ULSD
B20
PEMEX
PM (mg/mi)
2001
1990
394.41 ULSD 765.59
239.25
453.15
B20
407.54 PEMEX 488.74
Table B. 5. Average Emissions Index for Long-Haul Drive Cycle.
CO2 (g/kg fuel)
Drayage Trucks
Long-haul Trucks
1994
1995
1997
1999
2001
1990
1995
1999
2001
2004
3073.8 2979.45 3078.2 3117.15 2927.15 ULSD 2934.25 3059.05 2973
3081.7
2951
3070.6 2969.6 3020.15 3061.75 2952.7
B20 2964.55 2921.6 3095.75 3027.6 2996.35
3077.8 3085.41 3087.4 3055.75 2828.85 PEMEX 2986.4 2893.9 3106.3 3105.95 3014.05
1994
18.74
17.96
19.76
1995
33.66
22.73
24.7
1997
22.36
17.15
19.42
1999
9.99
10.13
10.34
CO (g/kg fuel)
2001
1990
5.17
9.95
ULSD
4.51
7.66
B20
5
PEMEX 7.28
1994
24.45
24.35
25.2
1995
31.79
34.74
33.25
1997
32.54
30.95
30.52
1999
26.84
28.34
28.33
NOx (g/kg fuel)
2001
1990
27.38 ULSD
21.76
29.63
23.72
B20
26.55 PEMEX 22.77
1995
49.4
41.06
41.6
1999
23.11
26.89
29.63
2001
25.12
25.41
25.14
2004
21.93
24.22
24.78
1994
0.58
0.36
0.57
1995
0.82
0.95
1.08
1997
1.48
1.24
1.45
1999
1.82
1.42
1.75
HC (g/kg fuel)
2001
1990
1.66
1.07
ULSD
1.47
0.84
B20
1.76 PEMEX 1.05
1995
0.94
0.77
0.63
1999
1.52
1.34
1.51
2001
1.88
1.67
1.69
2004
1.25
1.16
0.99
1995
21.53
14.03
20.58
1999
11.46
9.06
6.05
2001
4.32
4.86
4.73
2004
10.28
8.41
9.63
63
Table B. 6. Average Distance-Specific Emissions Rates for Long-Haul Drive Cycle.
CO2 (g/mi)
Drayage Trucks
Long-haul Trucks
1994
1995
1997
1999
2001
1990
1995
1999
2001
2004
2488.06 2102.21 2569.84 2521.47 2260.24 ULSD 2871.11 2333.15 2584.19 3060.29 2923.04
2518.1 1977.06 2477.65 2362.74 2340.57 B20 2670.11 2093.29 2672.41 2884.47 2882.88
2472.53 2054.16 2423.2 2350.65 2265.97 PEMEX 2669.17 2114.69 2819.28 3287.63 2828.76
CO (g/mi)
1994
15.34
15.3
16.15
1995
24.5
15.31
16.65
1997
19.08
14.65
17.03
1999
7.28
7.26
7.71
2001
2.97
2.67
2.99
1994
17.12
17.46
17.62
1995
21.23
22.37
21.41
1997
25.54
24.15
22.6
1999
20.6
20.9
20.86
2001
19.99
22.54
20.62
1994
0.31
0.19
0.29
1995
0.36
0.39
0.45
1997
0.93
0.76
0.82
1999
0.98
0.78
0.97
2001
0.89
0.79
0.97
1994
609.98
490.21
502.48
1995
368.29
250.64
265.68
1997
427.02
298.49
327.39
1999
262.42
222.87
236.3
ULSD
B20
PEMEX
1990
9.54
6.27
5.62
1995
15.74
11.17
17.01
1999
10.5
8.44
5.01
2001
3.61
3.81
4.22
2004
8.4
6.93
8.18
1990
19.28
18.9
17.88
1995
35.43
27.69
27.63
1999
18.71
21.34
25.79
2001
23.75
23.2
25.64
2004
21.29
22.21
21.71
1990
0.8
0.53
0.63
1995
0.41
0.38
0.3
1999
0.99
0.79
1.04
2001
1.39
1.25
1.44
2004
0.88
0.75
0.62
1995
235.47
186.2
229.51
1999
303.94
228.22
223.1
2001
393.98
244.44
308.78
2004
325.66
236.26
297.32
NOx (g/mi)
ULSD
B20
PEMEX
HC (g/mi)
64
ULSD
B20
PEMEX
PM (mg/mi)
2001
1990
260.87 ULSD 516.42
203.76
378.65
B20
222.95 PEMEX 376.09
65
APPENDIX C
66
68
69
70