2007 DEER Detroit August 12-16

Multicylinder Diesel Engine Design for HCCI operation

William de Ojeda

Phil Zoldak, Raúl Espinoza, Raj Kumar, Chunyi Xia, Dan Cornelius

International Truck and Engine Corporation

Diesel Engine DevelopmentDOE DEER CONFERENCE

Detroit, MichiganAugust 12-16, 2007

Acknowledgements: DOE LTC consortium project, Low Temperature Combustion Demonstrator for High Efficiency Clean Combustion (DE-FC26-05NT42413) .

Industrial Partners: UCB, LLNL, Siemens, ConocoPhillips, BorgWarner, Mahle, Ricardo. TM

1

2007 DEER Detroit August 12-16Goals and Objectives

• Overall goal: – Demonstrate the application of low temperature combustion (LTC) to

minimize in-cylinder emissions using today’s Diesel fuel. – The technology generated in project to be capable for production

implementation. • Phase I: Engine hardware simulation and design

• Phase II: Procurement and prove-out of main components:Fuel injectors, charge air-EGR system, control system with cylinder pressure feedback

• Phase III: Steady-state mapping • Phase IV: Transient and vehicle installation

• Key technical challenges addressed: - Optimization of fuel and charge air mixture to sustain LTC conditions - Improve stability of combustion with control system / VVA system - Minimize hydrocarbon emissions and maintain or improve bsfc - Accommodate a range of fuel properties representative of US geography

2

2007 DEER Detroit August 12-16Approach

Three pronged approach:

1. Thermodynamic engine modeling was done to select engine hardware to operate engine under LTC conditions (homogeneity,EQR) and deliver a max BMEP of 12.6 bar. Theresult is:

a. two-stage turbocharger, b. dual-parallel EGR system, c. low compression ratio piston

2. CFD-Kinetic combined modeling (mainlyperformed at LLNL) to optimize the injection and combustion chamber geometries.

3. Control Supervisor is used to integrate fueland air systems. Specially notable are:

a. coordinated boost/EGR systems b. fuel injection strategies specific to speed

and load b. development of a combustion close-loop

control based on in-cylinder pressuremeasurements.

4. Still under design / procurement: these are considered as enablers of LTC:

a. production like VVA system b. concept VCR

1

2

3 Illustration of engine design approach

3

2007 DEER Detroit August 12-16Engine Build

Base Engine: Common rail Single stage VNT turbochargerSingle EGR cooler.

Present build encompass:(1) Dual-path EGR system (2) Two-stage TC each with VNT stages (3) High-flow cylinder head (4) EGR mixture (5) Low CR pistons (6) Multi-hole injectors

1

2

3

4

1

4

2007 DEER Detroit August 12-16Next Engine Build: VVA system

Variable valve actuation system: • Electro-hydraulic system can provide

flexible intake valve closing times • IVC is applied to individual cylinders

and thus can provide effective “trimming”to balance cylinders.

• IVC can effectively reduce compression ratio and provide control over ignitiontime.

Simulation of VVA system at 3000rpm

Proposed layout of VVA system 5

2007 DEER Detroit August 12-16

Close-Loop-Controlto control combustion with multiple cylinders

Pressure and heat release traces without close feedback under HCCI operation

1

• Control system is based on cylinder pressure measurements

• System is applied to conventional combustion and to LTC like conditions. It is effective in reducing overallemissions by trimming fuel to each cylinder.

• Under conventional combustion, emissions improve only slightly. Under LTC conditions the effect is more pronounced, data shows soot may be reducedby up to 50%

2

Pressure and heat release traces with close feedback under HCCI operation

12

LTC Injection strategy94% NOx reduction

Close loop control:50% soot reduction

6

2007 DEER Detroit August 12-16Steady State Mapping

• Began steady • Developing strategy of combustion

approach based on emissions and fueleconomy performance. Keys are:

– Provide homogenization of fuel with charged air via FIE injection pattern (holesand size), single/multi-shot injections,injection timing.

– Target specific dilute conditions(equivalence ratio targets) via turbocharger hardware.

– Target EGR levels to suppresscombustion via EGR cooler / valving system

– Avoid wall impingement (key to minimize HC and BSFC penalties)

TQ (N

m)

700

600

500

400

300

200

100

0 0 1000 2000 3000 4000

rpm

4

5

tested points

6

LTC - Full load

1

LTC - Half load

2 3

Present operating map (squares) and test points.

Points 1,2,3 represent 50% loadPoints 4,5,6 represent 100% load.

7

NO

x (p

pm)

2

2007 DEER Detroit August 12-16Test Methodology

shift fuel into

Highlighted is the achievement ofLTC (low NOx/SOOT) with modestEGR levels and low injectionpressure relying on fuel-charge airmixing: 1. Fuel transfer from “main” near TDC to

early “pilot” shows the traditional NOx/SOOT tradeoff.

2. Fully premixed fuel reduces NOx by~85% (“cliff-event”)

3. The effect of close-loop fuel trimmingis illustrated

4. Injection timing is key to ensure fuel-charge air homogeneity as shown inthe loss of LTC from (3) to (4). Latterinjection timing returned combustionsystem to non-LTC like conditionswith high NOx and soot.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

0.00 0.20 0.40 0.60 0.80

FSN

Pilot ratio (PR) sweep PR = 1, LTC PR = 1, LTC - cylinder trimming PR = 1, no LTC

2007-05-14 1000rpm IMEP=3.3 bar EGR=20% FUP=50MPa

Pilot / Mainratio

(0.17 / 0.83)

(0.75 / 0.25)

1

3

4

(1 / 0)

(1 / 0)

NOx (

g/bh

p-hr

)

SOI Main to Target CA50~5º

CA ~ temp dependent 0 5

TDCcompression stroke

8

2007 DEER Detroit August 12-16The HC and BSFC Challenge

6000

The challenge of poor fuel economy and high HCs is 5000

illustrated here.

Conventional

High EGR

Low EGR

LTC

target

C

A

BHC

(ppm

) 4000

3000LTC like conditions are attained by shifting fuel into the compression stroke. 2000

Low temperature conditions are 1000 attained as shown in case C. The characteristic “cool” flame 0

chemistry appears. However HCs 200 250 300 350 400 450

and BSFC increasingly deteriorate. bsfc (g/kW-hr)

200

B A

C

HR

(J/d

eg)

150

100

50

0

-50-30 -20 -10 0 10 20 30

CA(deg) 9

A

2007 DEER Detroit August 12-16General Trends

1.8

1.6 Injection pressure is effective in reducing

200 250 300 350 400 450

bsfc (g/kW-hr)

Low FUP

Mid FUP

High FUP

targ

et

1.4 smoke / soot generation. 1.2

NO

x (p

pm)

FSN

1.0

0.8

0.6

0.4

0.2

0.0

700

EGR is effective in reducing NOx. 600

500

200 250 300 350 400 450

bsfc (g/kW-hr)

High EGR

Low EGR

target

NEXT:

EGR in combination with injection pressure and

400

300

OPTIMUM COMBUSTION TIMING AND 200

VAPORIZATION can lead to optimizing emissions 100

and HC/BSFC tradeoff to acceptable levels. 0

10

11

2007 DEERDetroit August 12-16

Optimizing Timing and EGRHelping to resolve the HC and BSFC challenge

Effect of EGR in ignition delay and emissions: higher EGR rates allow earlier injection timings (while holding CA50 constant). The longer ignition delay correlates with greater mixing times typical of LTC operation.

-80 -60 -40 -20 0 20 40 60 80 0

20

40

60

80

CA(deg)

P(b

ar)

-30 -20 -10 0 10 20 30

0

50

100

150

CA(deg)

HR

(J/d

eg)

The Effect of SOI in preparing the mixture is key: The injected fuel must vaporize (thus it must be injected at higher temperatures). The impact is great in minimizing BSFC and HC while maintaining NOx and soot emissions.

55%EGR 40%EGR

1000 rpm 150 Nm

SOI -12º 55%EGR

SOI -7º 40% EGR

2007 DEER Detroit August 12-16Summary

• Applied low temperature combustion (LTC) to minimize engine out emissions using today’sDiesel fuel.

• Approach for engine design combined thermodynamic engine modeling (based on prescribedEGR and EQR targets) to deliver a max BMEP of 12.6 bar, CFD-kinetic modeling to optimize theinjection and combustion chamber geometries, and a control supervisor to integrate fuel and airsystems.

The technology gathered is capable for production implementation: especially designed fuelinjectors, pistons, EGR system, turbocharger were procured. A VVA version of the engine is underway.

• LTC was achieved with high EGR levels as well as more modest EGR and injection pressures by relying on generating a fuel - charge air homogenous mixture.

Key technical challenges addressed are optimization of fuel and charge air mixture to sustain LTC conditions; limit engine out emissions, improve stability of combustion with control system, minimize hydrocarbon emissions and gain in bsfc The effects of EGR, intake manifold temperatures, injection pressures and injection timing were documented.

• A close-loop-control WAS successfully applied to conventional combustion and to LTC conditions to equalize cylinder torque and start of combustion. Data to date showed reduction of soot over 50%.

• Next steps is to extend the steady state mapping. The region currently being study extends between 6 – 12.6 bar. 12