The ABC’s Of
Exhaust Gas Recirculation (EGR)
Air Is A Mixture Of Gases,
Mostly Nitrogen & Oxygen
When air is compressed
inside the cylinder of a
diesel engine, the
temperature of the air is
increased enough to ignite
diesel fuel after it is injected
into the cylinder.
When the diesel fuel ignites,
the temperature of the air
increases to more than
1500° F and the air expands,
pushing the piston down
and rotating the crankshaft.
In General, The Higher
The Temperature, The
More Efficient The Engine
■ Good Performance
■ Good Fuel Economy
1
High Cylinder
Temperature
But, when peak
temperatures are high
enough for long enough
periods of time, the
nitrogen and oxygen in the
air combine to form new
compounds, primarily NO
and NO2.
High NOx
Formation
Zone
These are normally referred
to collectively as “NOx”.
Low Cylinder
Temperature
Too Much NOx In The
Atmosphere Contributes To
The Production Of Smog.
Since 1979, NOx emissions from diesel engines have been regulated by the EPA. In
October of 2002, new NOx standards required the diesel engine industry to introduce
additional technology to meet the new standards.
EPA Heavy-Duty Engine Emission Standards
1.1 g
0.01 g
Steady State
Test
NOx + HC
15
2007
NOx avg
PM
0.2 g
0.01 g
NOx
(Unregulated)
2.0
2010
NOx avg
PM
1.5
Useful Life
Transient Test
10
CD Transient &
+ Steady State
PM
(Unregulated)
CD Oct-02 Jan-04
NOx +
NMHC
NOx
PM
5
435K
290K
NOx
NOx
Consent
Decree
1.0
.5
Particulate Matter (g/bhp-hr)
20
Oxides of Nitrogen (g/bhp-hr)
The EPA has regulated heavyduty diesel engines since the
1970s. The following chart
shows the trend to ever-lower
emissions. Understanding the
details of the chart is not of
interest to most truckers.
Even though the emissions
standards become increasingly
more difficult to meet, the
diesel engine industry has
always been able to continue to
improve engine durability,
reliability, performance, and
fuel economy. A quick look at
the bottom right hand side of
the chart also shows that
emissions from diesel engines
built in 2007 and beyond will
approach zero.
PM
0
1970
1975
1980
1985
1990
Model Year
1995
2000
2005
.1
.0
2010
2
How Can NOx Be Reduced?
Since high cylinder temperatures cause NOx, NOx
can be reduced by lowering cylinder temperatures.
Charge air coolers are already commonly used for
this reason.
Reduced cylinder temperatures can be achieved in
two ways:
■ Retarding ignition timing
and/or
■ Reducing the amount of oxygen in the cylinder,
which inhibits the combustion process
Retarded ignition timing makes the combustion
process start at a less-than-optimum point and
reduces the efficiency of combustion.
This technique lowers cylinder temperature,
reducing NOx, But it also reduces fuel economy and
performance, and creates excess soot, which results
in more frequent oil changes.
3
Reducing Oxygen
In The Cylinder
The best way to reduce NOx is to limit the amount
of oxygen in the cylinder. Reduced oxygen results
in lower cylinder temperatures.
This is done by recirculating some exhaust gas (Exhaust Gas Recirculation)
into the cylinder. The effect is as follows:
High Cylinder
Temperature
High NOx
Formation
Zone
aximum
Cylinder
Temperature
with
Low Cylinder
Temperature
Since the whole idea is to reduce cylinder temperatures, it’s usually wise to
cool the exhaust gas before putting it back into the cylinder. This approach is
called “Cooled” EGR and is the technique used on the Detroit Diesel Series 50
and Series 60 engines. This technique will be used on the MBE 4000 and
MBE 900 after 1/1/04.
DDC has been using EGR
technology on the Series 50
since 2000 and has
produced a total of 40,000
Series 60’s with EGR since
October 2002.
EGR is so effective that it
allows ignition timing to
remain “advanced,”
improving performance
and fuel economy and
reducing soot.
4
How Does EGR Work?
EGR Is Required Only Under
Certain Conditions.
Turbocharger & EGR Valve
When EGR is required, the
engine’s electronic controls
open the EGR valve.
5
EGR Transfer Pipe (Hot)
The exhaust gases flow through
this pipe to the EGR cooler.
EGR Cooler
The exhaust gases are cooled
by water from the truck
cooling system.
EGR Transfer Pipe (Cool)
The cooled exhaust gases then
flow through the EGR transfer
pipe into the intake manifold.
6
Benefits Of Variable Geometry
Turbocharging (VGT)
Boost Pressure With VGT Turbocharger
50
00
urbocharger
250
Boost Pressure (kPa)
The turbocharger is equipped
with moveable vanes that
allow the engines electronic
controls to adjust the exhaust
pressure in the system,
ensuring that there is always
enough pressure for sufficient
EGR flow. (This type of
turbocharger is called a
Variable Geometry
Turbocharger, or VGT).
200
pical urbocharger
150
100
50
As a side benefit, engine
performance is improved and
the Jake Brake performance
is improved when a
VGT is used.
0
Idle Speed
Faster turbo response and quicker acceleration
A VGT is to a normal turbocharger as a
21-speed bike is to a single speed bike.
7
Maximum Engine Speed
There Are Other
Approaches To EGR
■ Internal EGR (Non-Cooled EGR)
This is accomplished by changes in valve timing that
allow exhaust gas to simply remain in the cylinder and
mix with the incoming air.
Internal EGR is inefficient and reduces fuel economy.
■ Reed-Valve Technology
This technology does not use a VGT and relies on
normal exhaust gas pulses in the exhaust manifold to
push exhaust gases through the EGR cooler and into
the intake manifold.
Reed-Valve is the name of the one-way valve in the
EGR transfer pipe that allows exhaust gases to enter
the intake manifold, but keeps the incoming fresh air
from entering the exit manifold.
Simple Reed-Valves Are Used
To Control The Flow Of EGR
How A Reed-Valve Works
The Reed-Valve is a
one-way “door” that allows
exhaust gas to flow into
the intake manifold but
prevents air in the intake
manifold from flowing back
into the exhaust system.
Pressure peaks in the
exhaust manifold open the
Reed-Valves.
Reed-Valve Open
Reed-Valve Closed
8
2004 Approach
To EGR Comparison
DDC
Series 60
MBE
Cooled EGR
VGT
✓
✓
✓
Reed
Internal EGR
✓
✓
CAT
Cummins
Volvo
Mack
✓
✓
✓
(On-Highway)
✓
✓
✓
(On-Highway)
✓
(Off-Highway)
__________________
Reed – Lower Cost, Lighter Weight (Turbo Brake)
VGT – Better Control, Better Response, Better Braking, Above 450 HP, Higher EGR Rates, Altitude,
More Flexibility to Adapt to Custom Ratings.
9
Other
Conclusions
■ EGR is
– Simple
– Proven
– Reliable
– Fuel Efficient
■ Reed-Valve
– Simple, Cost Effective
■ VGT
– More Adaptable
– Improves Driveability
– Improves Engine
Brake Performance
■ DDC EGR Engines Carry
The Same Warranty And Have
The Same Maintenance Intervals
As Non-EGR Engines.
10
13400 Outer Drive, West, Detroit, Michigan 48239-4001
Telephone 313-592-5000
www.detroitdiesel.com
© Copyright 2003 Detroit Diesel Corporation. All rights reserved. Detroit Diesel, the spinning arrows design, DDC®, DDEC® and Series 60®
are registered trademarks of Detroit Diesel Corporation.
06SA0591 0310 As technical advancements continue, specifications may change. Printed in U.S.A.