Advancement of Gasoline Direct Injection Compression Ignition (GDCI) for US 2025 CAFE and Tier3 Emissions
M. Sellnau, M. Foster, W. Moore, K. Hoyer, J. Sinnamon, B. Klemm
Delphi Powertrain
Auburn Hills, MI USA
June 14, 2017
2017 ERC Symposium
Motivation and Industry Challenge
2
• Stringent CAFE and CO2 targets with US Tier 3 emissions laws
• Changing demand for diesel and gasoline fuels worldwide
• Need efficient and clean engines operating on gasoline-like fuels
Fuel Economy
(United States)
Projected Fuel Demand
(World Energy Council, 2011)
Year
CAFE Target
(MPG)
CO2 Target
(gCO2/mile)
2011 27.6 322
2016 35.3 250
2025 54.5 163
Top Goals for Future Internal Comb. Engines
3
• Ultra high fuel efficiency
• Target: 200 g/kWh (42% thermal efficiency)
• Responsible use of non-renewable fossil fuels
• High well-to-wheel (WTW) fuel efficiency
• Minimize GHG emissions for life cycle of vehicle
• Includes CO2 emissions to process the fuel, manufacture vehicle, and combust fuel
• Ultra low criteria emissions both on cycle & off cycle (US Tier3-Bin30)
• NOx, HC, PM, CO, CH2O
Three Main GDCI Programs at Delphi
4
Delphi is partnered with leading industry experts to develop and
commercialize GDCI technology
US Dept of
Energy
4-Year
2014-2019
Develop GDCI Powertrain and
Demonstrate 35% improved FE with Tier3-
B30 Emissions in a practical vehicle
ORNL, Umicore, Univ of
Wisconsin-Madison
Saudi
Aramco
3-Year
2015-2018
Study Fuel Effects and Low Octane Fuels
on GDCI Combustion Saudi Aramco
ARPA-E
(DOE)
3-Year
2016-2018
Combine Opposed-Piston engine
technology with GDCI for best-in-class fuel
efficiency
Achates Power, Argonne
National Labs
Contents
5
• GDCI Concept
• Combustion System
• Injection System and Sprays
• Engine Test Results
• Emissions and Aftertreatment
• Summary
GDCI Combines the Best of Diesel & SI Technology
6
Medium CR SI Engines High CR CI Engines
• A new low-temp combustion process for Partially-Premixed CI
• Gasoline that vaporizes & partially mixes at low injection pressure
• High CR with late multiple injections (similar to diesel)
• High effic. & low NOx, PM over wide speed-load range
GDCI Engine Concept
7
• Gasoline Partially Premixed CI
• Fuel Injection
• Central Mounted, Multiple-Late Injection, GDi-like injection pressures
• Valvetrain – cont.-var. mechanical (exhaust rebreathing)
• Adv EMS – Cyl.-Pres.-Based Control
• No classic SI Knock or Preignition
• Down-sized, down-speeded, & boosted
• High CR, Lean, Unthrottled
GDCI Concept
Addressing all loss mechanisms for internal combustion engines
• 1, 2, or 3 injections on Intake and
Compression Strokes
• Complete injection & partial mixing
prior to start-of-comb.(PPCI)
• “Stratify”: robust ignition and
controlled heat release
• “Burn in the Box”: heat release below
Phi=1.2, 1200 < T < 2300 K
GDCI Injection Strategy – Phi-T Diagram
8
Q1
Q2
Q3
Injection
Events
“Burn in
the Box”
Simultaneously low NOx, PM, and CO is possible
Gen3 GDCI Combustion System
9
• “Wetless” concept for low smoke
• Inject at any SOI without wall wetting
• Wide spray angle matched to bowl
• Long stroke S/B=1.28 increases TDC clr space for late injections (D=2.22 liters)
• Zero swirl & squish for min. heat losses
• GCR: 16:1 (compression)
• Fast Intake Air Heating
• Cylinder Pressure Sensing
• Integral air-gap insulated exhaust manifold
• Pre-turbo catalyst (PTC)
Gen3 GDCI Injection System
10
• Centrally-mounted, GDi Injectors with high injection rate
• 350+ bar injection pressure
• Fuel pump driven by Intake Cam
• Sprays developed for fast atomization without wetting
• Goal: “wetless” combustion system for minimal smoke emissions
• Optimize spray and piston bowl design for both early and late injections
• Preinjections on intake stroke create premixed charge (PHI floor)
• Last injection late on compression stroke controls ignition; determines smoke and NOx emissions
Combustion System Development
CFD tools used extensively for spray development
• Plot shows injected fuel and vapor mass as function of time for SOI -45 to -25
• Injection period: 7 CAD (<0.6 ms)
• Very fast vaporization is observed, especially for late injections when cylinder gas temp. and pres. are high
• High cylinder gas temp. and pres. for late injections greatly reduce liquid penetration
• Major factor to reduce wall wetting
CFD Simulation of Injection Process
Vapor (dashed)
SOI -25
SOI -40
SOI -45SA 115o
Zero piston film for SOI -40 & later
Liquid (solid)
SOI -45
SOI -40
SOI -35
SA 125o
SA 130o
7a
7b
7c
7d
0 -10 -20 -30 -40 -50
Crank Angle Position (deg)
Mass /
To
tal In
jecte
d M
ass
Simulation Results: 3 Spray Angles
Vapor (dashed)
SOI -25
SOI -40
SOI -45SA 115o
Zero piston film for SOI -40 & later
Liquid (solid)
SOI -45
SOI -40
SOI -35
SA 125o
SA 130o
7a
7b
7c
7d
• Spray angle is a key factor in comb. system design
• Plots show piston and liner fuel mass as function of time for three spray angles (115, 125, 130 deg included)
• For spray angle 115, fuel wetting occurs for a range of SOI. Wetting persists at TDC and during combustion.
• For spray angle 125, fuel wetting is reduced
• For spray angle 130 and SOI later than -45, the injection process is “wetless”
• Conclude: wider spray angles of ~130 deg are preferred with Gen3 piston
Video
Spray Chamber Testing (UW-Madison)
• High Pressure & Temperature Chamber at UW-Madison (Ghandhi & Oakley)
• Non-reacting, flow-through type chamber
• Multi-plume configuration
• Plume oriented normal to axis of view
• Objectives: Characterize injectors, validate spray models
16
Backlit & Schlieren Images; Drop Size Measurement
• Liquid & Vapor penetration (Q=25mm3, 200bar)
• Low liquid penetration for higher chamber pressures
• Very small drop size (SMD) measured along spray plume (100bar)
Liquid
Vapor
Liquid
Vapor
High P&T Medium P&T
Pe
ne
tra
tio
n Room P&T
Spray
Plume
PDPA
SMD vs time
PDPA
SMD vs time
PDPA
SMD vs time
Liquid
at STP
17
Typical Combustion (1000rpm-3bar IMEP)
• Single Injection with exhaust rebreathing (SOI=40 btdc)
• Start-of-Combustion near TDC
• Low PMEP – rebreathing during intake stroke
• Stable, low-temperature combustion with good Texh
-100102030405060708090
0
10
20
30
40
50
60
-180 -135 -90 -45 0 45 90 135 180
HRR
(J/C
AD
)
Pcyl
(bar
)
Crank Position (CAD)
Pcyl
HRR
-0.5
0
0.5
1
1.5
2
1.4 1.6 1.8 2 2.2 2.4 2.6
Log
Pcyl
Log Vcyl
PMEP = 3 kPa
Measured Pcyl and Heat Release PV Diagram
BSFC - 1500 rpm Load Sweep
• BSFC significantly improved relative to Gen1 and Gen2 engines
• Low BSFC over a wide load range where the vehicle operates on drive cycle
• Near target: 200 g/kWh (~42% brake thermal efficiency)
• Exceptional light-load BSFC
• Small BSFC difference (~2%) attributed to aftertreatment system, which oxidizes unburned fuel prior to LP EGR system
18
190
200
210
220
230
240
250
260
270
280
290
0 200 400 600 800 1000 1200 1400
BSF
C (g
/kW
h)
BMEP(kPa)
Gen 1Gen 2
Gen3 Pre-breakin
NOx<0.6 g/kWhFSN<0.15
COV IMEP<3%Noise below target
12%
8%
3.4%
Target 200 g/kWh
Gen3 Active ATS
Gen3 Inert ATS
205 g/kWh
BSFC Benchmarking: 1500rpm-6bar IMEP
19
• GDCI is approx. 22% more efficient than SIDI turbo engine
• Approx. 11% more efficient than a leading 2.0L EU diesel
• Approx. 11% more efficient than 1.8L Atkinson engine (3rd Gen. Prius)
276
264
241 240
214
140
160
180
200
220
240
260
280
300
2.0L T-GDiRON91
2.4L SIDI NARON91
2.0L DieselULSD
1.8LAtkinson
RON91
Gen3 GDCIRON91
BSF
C (
g/kW
h)
-13% -13% -22%
GDCI has excellent part-load fuel economy relative to class leading
turbo SI and diesel engines
Reduced Smoke Emissions - 1500 rpm-11bar IMEP
• Smoke characteristic typically depends on injection timing
• Gen3 combustion system exhibits greatly reduced smoke
• Attributed to “wetless” combustion system
• Strong injection pressure dependency for Gen3
• Enables GDCI late injection with low smoke
• Further smoke reduction expected with latest injectors and sprays
20
Typical SOI
Window
High-Load Smoke Limit
Better
Gen2 245bar
Gen3 245bar
Gen3
380bar
Gen3 450bar
Emissions Challenges for Low-Temp Comb.
• Very challenging to achieve Tier3-Bin30 with low-temp combustion
• Low-temperature combustion equates to low-temp exhaust
• Engine out NOx and smoke are very low; HC and CO are SI-like
• Commercially viable technology must achieve very low TP emissions both on-cycle and off-cycle including high load.
• Clean EGR flows are imperative for good engine health (sticky components, compressor degradation, cooler fouling)
Gen3 Aftertreatment System (ATS) for Tier3- Bin30
22
EGR
Inte
gra
l
HCT
GOC
BPV
T SCRGOC
6x3”
600csi
HCT/GOC
1.35L
6x4”
NH3 SCR
1.82L
Urea
Dosing
Metal
GOC
0.14L
Catalyzd
GPF
6x3”
Passive
GPF
1.35L
• Heat conservation: compact, integral, air-gap insulated, exh. manifold
• HC/CO: Pre-turbo Cat w fast lightoff, HC Trap, GOC
• Particulates: catalyzed, passive GPF for off-cycle
• EGR feed stream post GPF
• NOx: close-coupled SCR system with urea evaporator
Pre-turbo Catalyst
Packaging: Gen3 Aftertreatment for T3B30
• Packaging is very compact for D-class passenger car
• Emphasis on heat conservation, short ducts, low space velocities
• Using Daimler SCR evaporator – good urea mixing and SCR temps
HF-EGR Cooler
HF-EGR Valve
HCT/GOC
GPF
SCR Doser &
Evaporator
PreTurbo Catalyst
SCR Catalyst
LF-EGR Valve
BP Valve
VNT Turbo
Close-Coupled SCR System (Gen3 GDCI)
0
20
40
60
80
100
150 200 250 300 350 400 450 500 550
NO
x C
on
vers
ion
%
SCR Temp [deg C]
NOx Conv. Effcy vs TSCR
NEDC
Steady
Urea
Evaporator
Plates
Close-coupled
SCR Cat.
Basin
HCT/GOC
cGPF
3D Simulation – Urea Dosing 1D Simulation – NOx Conversion
• 3D & 1D simulations used to develop dosing strategies
• 300 C needed for high NOx conversion efficiency
• Tier3-Bin30 NOx target may be achievable depending on light-off strategy
• Testing needed
24
Smoke Emissions – 1500rpm Load Sweep
• Low engine out (EO) smoke over low-to-medium loads
• A small gasoline particulate filter (GPF) exhibits high trapping efficiency (1.35L)
• TP smoke <0.02 over load range
• Testing planned to characterize particle size and number
• Overall, very good trapping efficiency for small particles.
25
EO and TP Smoke
-
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0 200 400 600 800 1000 1200 1400 1600
Smo
ke (
FSN
)
IMEP (kPa)
EO Smoke
TP SmokeEO Part-Load Smoke Limit
NOx and Exhaust Temp. – 1500rpm Load Sweep
EO NOx and Exhaust Temperatures
26
0
0.1
0.2
0.3
0.4
0.5
0.6
-
50
100
150
200
250
300
350
400
450
500
0 200 400 600 800 1000 1200 1400 1600
ISN
Ox
(g/k
Wh
)
Tem
per
atu
re (
deg
. C
)IMEP (kPa)
T PTC out
Tbed 1
Tbed 2
ISNOx
EO Part-Load NOx Limit
• Low EO NOx over low-to-medium load range (<0.6 g/kWh limit)
• SCR temp exceeds the critical 300 C at most operating conditions for high NOx conv. efficiency.
• SCR testing not yet completed
• Texh at PTC and GOC exceeds 300 C, even at low loads
• Texh increases with load; expected maximum <500 C.
EO and TP HC Emissions – 1500rpm Load Sweep
EO ISHC and TP NMHC Emissions
27
• Reasonable EO HC over low-to-medium load range
• TP NMHC are below target (10 ppm) at light-to-moderate loads; increasing above targets at higher loads
• Future tests:
• Low-temp. oxidation catalyst
• Cold start tests
-
20
40
60
80
100
120
140
160
180
200
-
1
2
3
4
5
6
7
8
9
10
0 200 400 600 800 1000 1200 1400 1600
TP N
MH
C (
pp
m C
3)
ISH
C (
g/kW
h)
IMEP (kPa)
ISHC
TP NMHC
TP NMHC Target
Summary – Gen3 GDCI
28
• GDCI technology is evolving with very stringent requirements for fuel efficiency, CO2 emissions, and criteria emissions.
• Preliminary dynamometer tests show:
• BSFC ~205 g/kWh for a wide load range
• Smoke was greatly reduced, especially for late SOI (“wetless” injection process)
• While very challenging, preliminary Texh & emissions data indicate good potential to meet Tier3-Bin30 targets
• More testing and engine calibration is needed ahead of vehicle implementation
Acknowledgements
29
Delphi gratefully acknowledges support from the US Department of Energy (Gurpreet Singh and Ken Howden)
Questions?
