EVALUATION OF CURRENT AND FUTURE ATKINSON
ENGINE TECHNOLOGIES
2nd CRC Advanced Fuel and Engine Efficiency Workshop 11/2/2016
Charles Schenk, U.S. EPA
Developmental data: internal EPA use only
1
Background
• As part of the rulemaking establishing the model year (MY) 2017‐2025 light‐duty vehicle GHG standards, EPA made a regulatory commitment to conduct a Midterm Evaluation (MTE) of longer‐
term standards for MY 2022‐2025.
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https://www3.epa.gov/otaq/climate/mte.htm
Work began immediately following the 2012 FRM
Draft TAR released for public comment 7/16
Comment period closed in 9/16
• In 2012, Mazda introduced their SkyActiv‐G family of engines in the U.S.
– Notable characteristics:
• First implementation of Atkinson Cycle outside of HEVs/PHEVs (as far as we knew)
• Very high geometric compression ratio (13:1 U.S., 14:1 E.U. and Japan)
• EPA engineering staff thought it warranted a closer look and added SkyActiv‐G to the list of engines and transmissions that would be benchmarked as part of our powertrain technology assessment activities
– Benchmarking and model data used in MTE Technical Assessment Report (TAR)
• Subsequently other Atkinson engines have been released – Toyota ESTEC 2GR‐FKS/FXS V6, SAE 2015‐01‐1972; 1NR‐FKE 1.3L I3 and 2NR‐FKE 1.5L I4 cEGR/Atkinson
– Hyundai Kappa 1.6L GDI, SAE 2016‐01‐0667; Nu 2.0L PFI
2
Benchmarking results
on the 2014 U.S. Mazda 2.0L engine
3
Benchmarking Overview
• Benchmarked Mazda 2.0L (13:1 CR) engine
• Tier 2 E0 93 AKI
• Tier 3 E10 86 AKI
• Implemented into Hardware‐in‐Loop (HIL) test bed
• Validated to baseline vehicle test data
• Tested engine in a simulated future vehicle
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Benchmarking
• Engines fully instrumented
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CAN data for available EPIDs
All ECU I/O measured and logged
Cylinder pressure on all cylinders
Exhaust emissions
Temperatures, pressures, etc.
• SAE Papers
– 2016‐01‐1007 “Benchmarking and Hardware‐in‐the‐Loop Operation of a 2014 MAZDA SkyActiv 2.0L 13:1 Compression Ratio Engine”
– 2016‐01‐0565 “Air Flow Optimization and Calibration in High‐Compression‐ Ratio Naturally Aspirated SI Engines with Cooled‐EGR”
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Mazda 2.0L Engine Benchmarking
Atkinson Cycle
•Effects of LIVC cam phasing:
•
Allows high geometric expansion ratio (13:1)
•
Reduced effective compression ratio
− Varies from 5‐11 due to intake cam phasing
− Decreases in‐cylinder temperatures and knock sensitivity
•
Reduced pumping losses (at throttle)
SAE Technical Paper 2016‐01‐1007
6
Benchmarking
Intake Cam Phasing for Atkinson Cycle
Intake retard from latest IVC
Intake manifold pressure (kPa)
Atkinson
Internal EGR
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Benchmarking
Some improvement with Octane
LEV III Fuel (E10, 88 AKI)
Tier 2 Certification Fuel (E0, 93 AKI)
-No change in torque curve from octane
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Benchmarking
93 AKI – 88 AKI comparisons
BTE (93 AKI) – BTE (88 AKI) (%)
+3% BTE max
Spark (93 AKI) – Spark (88 AKI) (BTDC)
+6° spark
FTP
HWFET
-Efficiency differences mostly along the low speed torque curve
-Caused by spark advance allowed by higher octane
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Hardware in the loop (HIL) cycle testing
on the 2014 U.S. Mazda 2.0L engine
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Engine Hardware‐in‐Loop (HIL) Testing
Vehicle Configuration
• VSIM (EPA’s vehicle HIL model) is based on EPA’s full vehicle simulation ALPHA model
• Allows test cell to “drive” an engine as a virtual vehicle
• Can infinitely vary:
– Drive cycle
– Vehicle test weight and road loads
– Transmission parameters
• Shift logic controlled by ALPHAshift
‒ Optimizes gearing for best efficiency
• Simple transmission thermal model used to calculate higher losses of cold transmission
during FTP
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HIL Testing Baseline
Cycle Validation
• Validated VSIM with 2.0L SkyActiv to 2014 Mazda3 chassis test data
• Compared key characteristics to actual vehicle CAN bus data
‒ Engine speed, gear, fuel flow
Cycle mph
Chassis
Engine
Engine Speed
Gear
Total Fuel (g)
SAE Technical Paper 2016‐01‐1007
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HIL Testing Baseline
Fuel Economy
Baseline vehicle
Bag 1
35.0
35.0
35.5
Average
35.2
Cert data
35.1
% error
0%
Bag 2
36.5
36.6
36.9
36.7
37.9
‐3%
Bag 3
42.8
42.8
42.7
42.8
43.1
‐1%
FTP
37.7
37.8
38.1
37.9
38.6
‐2%
HWFE
58.5
58.8
58.6
58.6
56.9
3%
• Three repetitions completed for each tested configuration
‒ Baseline and future vehicles
• Standard test-test variability was very small for all cases
• Baseline HIL data correlated well with 2014 Mazda3 certification test data
SAE Technical Paper 2016‐01‐1007
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HIL Testing Future Vehicle
Specification
• Unmodified 2014 Mazda 2.0L engine (same as baseline HIL case)
• Approximated with 2025 midsize car • Assumed footprint of current Mazda6
• Maintained baseline acceleration performance (power/weight)
• Added features to 2025 midsize car:
– Future 8-speed transmission
• Based on current 8-speed ZF transmission (8HP50)
• Includes expected reductions in spin and pump losses
– Active trans warmup (assume thermal loop)
– Stop-start (calculation adjustment only)
– Road load reductions (two levels, L1 and L2)
SAE Technical Paper 2016‐01‐1007
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HIL Testing Future Vehicle
Road Load
• Used a “reference road load” based on average of several high‐volume 2008 midsize cars to properly reflect reductions in the Federal Rulemaking (FRM) • Applied road load reductions in two levels (L1, L2) • 2008 Mazda6 was almost identical to average 2008 vehicle
SAE Technical Paper 2016‐01‐1007
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HIL Testing Future Vehicle
Road Load
• Starting with 2008 reference road loads, applied two levels of reductions:
Level
Weight
Reduction
Rolling Resist.
Reduction
CdA
Reduction
L1
L2
10%
15%
20%
30%
20%
25%
• Resulting in the following test coefficients for 2025 midsize car L1 and L2:
2008 Mazda6
ETW
A (lb)
B (lb/mph)
C (lb/mph2)
CRR
CdA (m2)
3625
29.7
0.3810
0.01811
0.0089
0.76
2025 Midsize Car
L1
3250
24.3
0.0279
0.01765
0.0071
0.60
2025 Midsize Car
L2
3125
22.5
0.1622
0.01456
0.0062
0.57
SAE Technical Paper 2016‐01‐1007
16
HIL Testing Future Vehicle
Fuel Economy
• Cycle test results of Skyactiv 2.0L engine as 2025 midsize car (mpg): 2025 midsize car L1
Bag 1
40.6
40.7
40.5
Average
40.6
Bag 2
39.3
38.6
38.3
38.7
Bag 3
45.7
45.6
45.5
45.6
FTP
41.2
40.8
40.6
40.9
HWFE
64.9
64.5
64.2
64.5
2025 midsize car L2
Bag 1
41.5
41.6
41.6
Average
41.6
Bag 2
39.8
40.3
40.0
40.0
Bag 3
46.7
47.0
46.8
46.8
FTP
41.9
42.3
42.1
42.1
HWFE
67
67.2
67.1
67.1
• These are raw results, prior to adjustment for assumed stopstart operation
SAE Technical Paper 2016‐01‐1007
17
HIL Testing Future Vehicle
Fuel Economy with Idle Start‐Stop
• Made adjustments assuming the 2025 midsize car would be equipped with a stop‐start device
• Enable conditions:
– > 120s run time AND
– Coolant temp > 80C
2025 midsize car L1: start‐stop adjustments ‐ CBE corrected
Total
Idle
Adj total
FE
FE adj
Bag 1
247.3
4.3
242.9
40.6
41.3
Bag 2
278.3
18.4
259.9
38.7
41.5
Bag 3
230.4
9.4
220.9
45.6
47.5
FTP total 257.9
12.8
245.1
40.9
43.0
HWFE
64.5
Combined
50.6
g/mi adj
215.0
214.3
186.9
206.7
137.7
175.6
2025 midsize car L2: start‐stop adjustments ‐ CBE corrected
Total
Idle
Adj total
FE
FE adj
Bag 1
241.7
3.9
237.8
41.6
42.2
Bag 2
269.0
17.6
251.4
40.0
42.8
Bag 3
214.3
9.0
205.4
46.8
48.9
FTP total 247.6
12.2
235.4
42.1
44.3
HWFE
67.1
Combined
52.3
g/mi adj
210.4
207.5
181.8
200.8
132.4
170.0
SAE Technical Paper 2016‐01‐1007
18
HIL Testing Future Vehicle
Results
• FTP and HWFET cycles (combined) for the 2025 midsize cars yielded 170‐176 g/mi CO2 (L2 results shown below)
Total
Idle
Adjusted
FE
g/mi
Bag 1
Bag 2
Bag 3
FTP (total)
HWFE
Combined
Fuel (g)
241.7
269.0
214.3
Fuel (g)
3.9
17.6
9.0
Fuel (g)
237.8
251.4
205.4
(mpg)
42.2
42.8
48.9
CO2
210.4
207.5
181.8
247.6
12.2
235.4
44.3
67.1
52.3
200.8
132.4
170.0
• The 2025 GHG compliance level for a midsize car with a 48 ft2 footprint is 154 g/mi
• Possible A/C credits anticipated to be up to 18.8 g/mi
• This suggests a target range of 154‐173 g/mi
The HIL test results suggest this hypothetical vehicle has the potential to
obtain compliance levels with the existing 2.0L Skyactiv engine
SAE Technical Paper 2016‐01‐1007
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GT-POWER Atkinson engine futuring
14:1 CR, cooled EGR (cEGR), cylinder deactivation (CDA)
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GT‐POWER Validation
13:1 Engine Benchmarking Data
• Fuel: 42.9 MJ/kg, 96 RON Tier 2 certification gasoline (E0)
• Dynamometer test data over more than 200 speed and load points
• GT‐Power Maps ‐ generated from 0.5 bar to 13 bar BMEP
– Modeled BSFC was significantly higher below ~0.5 bar BMEP load and GT‐Power sometimes estimated unreasonably high BSFC at 0 bar BMEP. BSFC at below 0.5 bar BMEP was therefore estimated by using a low fidelity extrapolation method.
SAE Technical Paper 2016‐01‐0565
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GT‐POWER Modeling
14:1 and cEGR
• Incremental FC effectiveness of cEGR alone: ~ 2‐5%
• Incremental FC effectiveness of cEGR + 14:1 CR: ~ 4‐5%
SAE Technical Paper 2016‐01‐0565
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GT‐POWER Modeling
14:1, cEGR, and CDA
2 cylinder deac/4
2 cylinder deac/6
BSFC
Combined cEGR and CDA
-BSFC reduction from reduced pumping losses at partial load
SAE Technical Paper 2016‐01‐0565
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Future Work
• Proof‐of‐concept engine development based on 14:1CR 2.0L EU version of the engine
– cEGR
2017 SAE Congress paper
– CDA
– Combustion improvements
• Make further improvements to GT Power Model – Further model validation as data becomes available
• Validate EGR and kinetic knock models
• Burn duration
• Model a larger DOE space
– Sweep EGR rates, spark timing & camshaft phasing within model
– Explore use of MathWorks model‐based “Calibration Toolbox” for rapid development of engine control and calibration
• Further investigate conditions and limitations for implementation of cylinder deactivation
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