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Developmental data: internal EPA use only

EVALUATION OF CURRENT AND FUTURE ATKINSONENGINE TECHNOLOGIES

2nd CRC Advanced Fuel and Engine Efficiency Workshop 11/2/2016

Charles Schenk, U.S. EPA

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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.– 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

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Benchmarking resultson the 2014 U.S. Mazda 2.0L engine

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– 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 BenchmarkingAtkinson 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)

6SAE Technical Paper 2016‐01‐1007

BenchmarkingIntake Cam Phasing for Atkinson Cycle

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Intake retard from latest IVC

Internal EGR

Atkinson

Intake manifold pressure (kPa)

BenchmarkingSome improvement with Octane

LEV III Fuel (E10, 88 AKI) Tier 2 Certification Fuel (E0, 93 AKI)

8-No change in torque curve from octane

Benchmarking93 AKI – 88 AKI comparisons

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-Efficiency differences mostly along the low speed torque curve-Caused by spark advance allowed by higher octane

+6° spark

BTE (93 AKI) – BTE (88 AKI) (%) Spark (93 AKI) – Spark (88 AKI) (BTDC)

+3% BTE max

FTPHWFET

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Hardware in the loop (HIL) cycle testingon the 2014 U.S. Mazda 2.0L engine

Engine Hardware‐in‐Loop (HIL) TestingVehicle 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 BaselineCycle 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

Engine Speed Gear Total Fuel (g)


ChassisEngine

Cycle mph

HIL Testing BaselineFuel Economy

Baseline vehicleBag 1 Bag 2 Bag 3 FTP HWFE35.0 36.5 42.8 37.7 58.535.0 36.6 42.8 37.8 58.835.5 36.9 42.7 38.1 58.6

Average 35.2 36.7 42.8 37.9 58.6Cert data 35.1 37.9 43.1 38.6 56.9% error 0% ‐3% ‐1% ‐2% 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


HIL Testing Future VehicleSpecification

• 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)


HIL Testing Future VehicleRoad 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


HIL Testing Future VehicleRoad Load

• Starting with 2008 reference road loads, applied two levels of reductions:

• Resulting in the following test coefficients for 2025 midsize car L1 and L2:

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LevelWeight

ReductionRolling Resist.

ReductionCdA

ReductionL1 10% 20% 20%L2 15% 30% 25%

2008 Mazda6 2025 Midsize Car

L1 2025 Midsize Car

L2 ETW 3625 3250 3125

A (lb) 29.7 24.3 22.5 B (lb/mph) 0.3810 0.0279 0.1622 C (lb/mph2) 0.01811 0.01765 0.01456

CRR 0.0089 0.0071 0.0062 CdA (m2) 0.76 0.60 0.57

SAE Technical Paper 2016‐01‐1007

HIL Testing Future VehicleFuel Economy

• Cycle test results of Skyactiv 2.0L engine as 2025 midsize car (mpg):

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2025 midsize car L1Bag 1 Bag 2 Bag 3 FTP HWFE40.6 39.3 45.7 41.2 64.940.7 38.6 45.6 40.8 64.540.5 38.3 45.5 40.6 64.2

Average 40.6 38.7 45.6 40.9 64.5

2025 midsize car L2Bag 1 Bag 2 Bag 3 FTP HWFE41.5 39.8 46.7 41.9 6741.6 40.3 47.0 42.3 67.241.6 40.0 46.8 42.1 67.1

Average 41.6 40.0 46.8 42.1 67.1

• These are raw results, prior to adjustment for assumed stop-start operation


HIL Testing Future VehicleFuel 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 correctedTotal Idle Adj total FE FE adj g/mi adj

Bag 1 247.3 4.3 242.9 40.6 41.3 215.0Bag 2 278.3 18.4 259.9 38.7 41.5 214.3Bag 3 230.4 9.4 220.9 45.6 47.5 186.9

FTP total 257.9 12.8 245.1 40.9 43.0 206.7HWFE 64.5 137.7

Combined 50.6 175.6

2025 midsize car L2: start‐stop adjustments ‐ CBE correctedTotal Idle Adj total FE FE adj g/mi adj

Bag 1 241.7 3.9 237.8 41.6 42.2 210.4Bag 2 269.0 17.6 251.4 40.0 42.8 207.5Bag 3 214.3 9.0 205.4 46.8 48.9 181.8

FTP total 247.6 12.2 235.4 42.1 44.3 200.8HWFE 67.1 132.4

Combined 52.3 170.0

HIL Testing Future VehicleResults

• FTP and HWFET cycles (combined) for the 2025 midsize cars yielded 170‐176 g/mi CO2 (L2 results shown below)

• 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

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TotalFuel (g)

IdleFuel (g)

AdjustedFuel (g)

FE(mpg)

g/miCO2

Bag 1 241.7 3.9 237.8 42.2 210.4Bag 2 269.0 17.6 251.4 42.8 207.5Bag 3 214.3 9.0 205.4 48.9 181.8

FTP (total) 247.6 12.2 235.4 44.3 200.8HWFE 67.1 132.4

Combined 52.3 170.0

The HIL test results suggest this hypothetical vehicle has the potential to obtain compliance levels with the existing 2.0L Skyactiv engine


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GT-POWER Atkinson engine futuring14:1 CR, cooled EGR (cEGR), cylinder deactivation (CDA)

GT‐POWER Validation13:1 Engine Benchmarking Data

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• 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

GT‐POWER Modeling14:1 and cEGR

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• Incremental FC effectiveness of cEGR alone: ~ 2‐5%• Incremental FC effectiveness of cEGR + 14:1 CR: ~ 4‐5%


GT‐POWER Modeling14:1, cEGR, and CDA

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2 cylinder deac/4 2 cylinder deac/6 BSFCCombined cEGR and CDA

-BSFC reduction from reduced pumping losses at partial load


Future Work

• Proof‐of‐concept engine development based on 14:1CR 2.0L EU version of the engine– cEGR– 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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2017 SAE Congress paper

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