AIR FLOW OPTIMIZATION AND CALIBRATION
IN HIGH-COMPRESSION-RATIO NATURALLY
ASPIRATED SI ENGINES WITH COOLED-EGR
SoDuk Lee, Ph.D, Charles Schenk and Joseph McDonald
North America GT Conference 2016
November 14, 2016
U.S. EPA - Office of Transportation and Air Quality
Assessment and Standards Division
Ann Arbor, Michigan, USA
Contents

Background

Model Calibration and Validation


Development of GT-POWER Model inputs

Model Validation with Dynamometer Test Data
Modeling Potential Engine Technology Changes

Compression Ratio (CR), cEGR, Cylinder Deactivation (CDA)

CR + cEGR + CDA Effects

Summary & Future Work

Acknowledgement
2
Background
-SkyActiv-G Engine Benchmarking
Intake retard from latest IVC
BTE (%)
200
135 kW
33
120 kW
36
34
36
35
34
105 kW
33
90 kW
36
32
37
36
75 kW
34
33
36
100
35
34
32
33
32
35
5
35
37
35
150
34
33
34
60 kW
30
45 kW
33
32
50
30
28
26
23
20
15
10
0
1000
28
28
26
26
23
20
15
10
5
2000
Internal EGR
Speed (RPM)
Intake manifold pressure (kPa)
30 kW
23
20
15 kW
15
10
3000
7.5 kW
5
5
4000
5000
6000
Speed ( RPM )
Speed (RPM)
Speed (RPM)

U.S. 2.0L I-4 13:1CR Mazda SkyActiv-G engine results shown above

Significant variation of effective compression ratio


Torque (N-m)
0
30
Torque (N-m)
32
10
Torque ( Nm )
BMEP ( Bar )
BMEP (bar)
Torque (N-m)
32
Torque (N-m)
Effective Compression Ratio
Atkinson
Less use of ETC for throttling & reduced pumping losses
Highest brake thermal efficiency measured by EPA to date for a NA engine

Also very good part-load efficiency
Speed (RPM)
3
Modeling Background

U.S. 2.0L Skyactiv-G (13:1 CR)
(Dyno Benchmarking Results)
1.0L Ricardo “EGRB” 27-bar BMEP
(Modeling Results)
Peak BSFC of 2.0L 13:1 CR Mazda SkyActiv-G
Engine:

Close to 27-bar Ricardo EGRB configuration
analyzed in the 2012 FRM for 2017 -2025 LightDuty Vehicle GHG Emissions

Ricardo EGRB: 1.0L, cEGR, integrated exhaust
manifold (IEM) with split-cooling, VVL,
95 RON E0 (2010 analysis conducted for 2012
FRM)

EGRB has a broader area of low (<240 g/kW-hr)
BSFC and high (35%) BTE which extends to lower
speeds and loads
4
Modeling Background

Assess the effectiveness of future engine technologies for greenhouse gas (GHG) emission
reduction

Study Impacts of:


Compression ratio changes

Cooled EGR (cEGR)

Cylinder deactivation (CDA)

Intake/Exhaust Cam Phasing, CA50, cEGR Calibration Development, etc
Conduct GT-POWER 1-D gas dynamics/combustion model parametric study

Explore whether or not BSFC comparable to highly-boosted/downsized engines could be
achieved with a simpler, naturally aspirated, stoichiometric combustion approach

Eventually expand modeling efforts to encompass other engines and approaches

To rapidly tuning intake and exhaust cam phasing for controlling and balancing internal EGR and
external cEGR while satisfying the constraints of engine knock, etc.
5
Development of Model Inputs

Engine geometry, intake/exhaust valve dimensions and events, valve cam lift profiles,
friction estimates, airflow tests, instrumented engine benchmarking

Intake manifold geometry and plenum volume were difficult to quantify


Estimated air-box and plenum volumes via water filling measurements
Cooled EGR system

CFD modeling and initial system prototyping conducted under contract with SwRI
2.5L Skyactiv-G Mazda Engine Injection End Time - in 720°
Injector Delivery Rate: ~15 g/s
GT-POWER Formula
6
Development of Model Inputs
2.0L SkyActiv-G@4500 RPM WOT
2.0L SkyActiv-G@4500 RPM WOT
Crank Angle Based
Intake & Exhaust
Pressure Traces

Three pressure analysis (TPA)


GT-POWER model matched measured incylinder pressure traces reasonably well
Data for three pressures referenced to crank angle were needed at different engine operation conditions

Intake port, exhaust port and in-cylinder pressures
 Measurements of engine-out (pre-catalyst) exhaust emissions

Used for validation of modeled end-gas concentrations
7
Model Validation @ Full Load
MAP

13:1 CR 2.0L SkyactivG engine model
simulations and test
data are in good
agreement

Avg. BSFC differences
~= 3% (1 to 5%)
BMEP
Exhaust Back Pressure
BSFC
8
Model Validation @ Part Load Conditions
MAP

Model simulations
and test data are in
good agreement

BSFC differences at
partial loads may be
due to errors in
estimated FMEP

Work is continuing
to develop better
estimates of firing
FMEP
BMEP
Exhaust Back Pressure
BSFC
9
Modeling Potential Engine Technology Changes
-OEM Mazda SkyActiv-G 13:1 CR Base Engine Maps
Dynamometer Testing
BTE (%)
BSFC (g/kWh)
GT-POWER Model
BSFC (g/kWh)
Model estimated BSFC
was higher below 0.5 bar
BMEP load and GTPOWER 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.
Engine Speed [RPM]

Fuel: 42.9 MJ/kg LHV, 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
10
Modeling Potential Engine Technology Changes
-Effectiveness of Cooled EGR (cEGR)

Incremental FC effectiveness of cEGR alone: ~ 2-5%

Incremental FC effectiveness of cEGR + 14:1 CR: ~ 4-5%
13:1 CR -> 14:1CR
Modeled BSFC with
Initial cEGR SwRI Table
GT-POWER cEGR /w PID
∆BSFC [%] with cEGR
cEGR & 14:1 CR
Tom Leone et el,
Environmental Science and Technology 2015
11
Modeling Potential Engine Technology Changes
-Cylinder Deactivation (CDA)

2 cylinder deactivation with VVT (DCP)

BSFC reduction from reduced pumping losses at partial load

Modeled fuel injectors individually

Implementation of CDA sets intake & exhaust valve lifts to zero and shuts off spark

Earlier intake valve opening used to achieve the desired air flow and BMEP levels

IVO @ ~-30° during CDA improved BSFC
CDA Effectiveness
Intake Valve Opening Optimization
SkyActiv-G w/CDA
(Modeled)
Δ BSFC
GM 4.3l V6 w/CDA
(Measured, SAE 2016-01-0662)
Δ BSFC
12
Modeling Potential Engine Technology Changes
14:1 CR + cEGR + CDA - What is the potential for improvement?
Δ BSFC
BSFC
BTE %
Engine Speed [RPM]

Some synergies between cEGR and CDA

Not fully explored within DOE of modeling runs
13
Model Validation of Future Technology- cEGR
The Futured, SAE 2016-01-0565
SWRI Target
Model /w PID
SAE 2016-01-0565
Dyno Test
• The Predicted BSFC <= 3% except the mode 6 (4%)
• Mode 6: 10% Modeled cEGR rates and 15% EGR engine dyno tests
- SWRI DCO (Dual Coil Offset) Ignition System
• iEGR is more effective at the very Light Loads like Mode 4
• Updated cEGR engine map & calibrations will be published
- The outside of cEGR region = The base engine operation
14
The CDA Model Validation
GM 4.3l V6 w/CDA
(Measured, SAE 2016-01-0662)





Removed the rocker arms to emulate cylinder 2 and cylinder 3 CDA
The modeled BSFC are within the range of the CDA map effectiveness
The measured CDA effectiveness deteriorated when increasing engine loads
The CDA effectiveness is lower at the mode 10
CDA + cEGR transition points may be higher with the CDA air spring effect.
- 2.0L CDA w/o cEGR operation: 5.5 bar BMEP at 4000 rpm [1]
1. Hitomi, M, “Our Direction for ICE – Consideration of Engine Displacement,” 36th Internationales Wiener Motoren Symposium, 2015
15
Summary


Conducted engine dynamometer benchmark testing of the U.S. and EU 2.0L &
U.S. 2.5L Mazda Skyactiv-G Engines at EPA-NVFEL

Selected 2.0L Engine for technology effectiveness evaluation

Low-pressure cEGR proof-of-concept under development at NVFEL
Developed and validated GT-POWER engine model

Explored use of a kinetic knock model to investigate engine knock mitigation for a geometric
CR increase and cEGR implementation

VVT, CDA, cEGR, CR and other technology and calibration effects are investigated by DOE

Updated the original model with the recent cEGR and CDA engine dyno test data

Applied the engine model to accelerate engine hardware calibration and control development
16
Future Work


Proof-of-concept engine development based on 14:1 CR 2.0L EU version of the engine

cEGR and CDA – will be published

Combustion improvements

Use model to assist with calibration and full load torque curve
development during engine dynamometer tests
Make further incremental improvements to GT Power Model



Further model validation as additional 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
17
Acknowledgments

FEV for the initial model build of GT-POWER using the 2.5L Mazda Skyactiv-G
engine as well as additional associated testing and measurements

SWRI for initial cooled EGR system design, modeling, and development

Mr. Paramjot Singh at Gamma Technology for his extensive assistance and GTPOWER technical support

Mr. Greg Davis at U.S. EPA-NVFEL for measurement of the 2.0L Mazda
Skyactiv-G engine geometry, volumes, cam profiles, etc.
18