Advancement of Gasoline Direct Injection Compression ... · Advancement of Gasoline Direct Injection Compression Ignition (GDCI) for US 2025 CAFE and Tier3 Emissions M. Sellnau, M.

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?