Daniel Flowers, Salvador Aceves, Joel Martinez, Francisco EspinosaLawrence Livermore National Laboratory

and Robert Dibble

University of California, Berkeley

DEER MeetingNewport, RI

August 26, 2003

Detailed Modeling of HCCI and PCCI combustion and Multi-cylinder HCCI Engine Control

We have developed and continue to improve the most advanced analysis tools for HCCI combustionThrough our collaborations we have applied these tools to a

wide variety of industrially significant questions:– What effect does turbulence have on HCCI combustion?

• Completed study of Lund TD100 engine for low turbulence geometry, now conducting simulations on high turbulence geometry

– What are the low load limits to HCCI operation?• Study of HCCI low-load operation limits in Sandia engine

– Does mixing affect CO emissions in HCCI combustion?• Extended multi-zone model includes mixing effects –

framework for general tool to analyze of HCCI, PCCI, SCCI• Analyzed post-combustion mixing and CO formation in

HCCI engine

Our detailed chemical kinetics codes and optimization software guide our experimental control efforts

• What control methods are viable for multi-cylinder HCCI engines?– Designed and tested a generic control system for internal

EGR control of cylinder by cylinder variation in 4-cylinder engine

– Implementing closed loop feedback control for cylinder-by-cylinder phase balancing

Outline

Through our collaborations we have applied these tools to a wide variety of industrially significant questions:– What effect does turbulence have on HCCI combustion?

• Completed study of Lund TD100 engine for low turbulence geometry, now conducting simulations on high turbulence geometry

– What are the low load limits to HCCI operation?• Study of HCCI low-load operation limits in Sandia engine

– Does mixing affect CO emissions in HCCI combustion?• Extended multi-zone model includes mixing effects – framework

for general tool to analyze of HCCI, PCCI, SCCI

• Analyzed post-combustion mixing and CO formation in HCCI engine

What is the role of turbulence in HCCI engines?

• Lund Institute studied HCCI operation in high and low turbulenceengines

• These experiments showed that burn durations in higher turbulence configuration were significantly longer

• Debate raised about turbulence influence on the ignition process• We conjecture that chemistry timescales are far too rapid to be

affected by local turbulence timescales

Lower turbulence piston crown

Higher turbulence piston crown

We have completed simulations with the flat-top (lower turbulence) geometry that agree very well with experiments

Flat piston (Disc) p=2 bar, Φ=0.40

0

10

20

30

40

50

60

70

80

90

100

-10 -5 0 5 10 15 20 25 30CAD

Pres

sure

, bar

T=469T=463T=457T=453T=451T=450P_dcT451P_Dc443P_DcT436P_Dc429P_DcT433P DcT431

Solid lines: numericalDotted lines: experimental

Simulations have been completed for the low turbulence case, high turbulence case is in progress

Flat crown (60K cells) Square Bowl Crown (400K cells)

Outline

Through our collaborations we have applied these tools to a wide variety of industrially significant questions:– What effect does turbulence have on HCCI combustion?

• Completed study of Lund TD100 engine for low turbulence geometry, now conducting simulations on high turbulence geometry

– What are the low load limits to HCCI operation?• Study of HCCI low-load operation limits in Sandia engine

– Does mixing affect CO emissions in HCCI combustion?• Extended multi-zone model includes mixing effects – framework

for general tool to analyze of HCCI, PCCI, SCCI

• Analyzed post-combustion mixing and CO formation in HCCI engine

Experiments in the Sandia HCCI engine show very inefficient combustion as equivalence ratio is reduced

Experimental isooctane HCCI data from the Sandia Engine

0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28Equivalence ratio

0

10

20

30

40

50

60

70

80

90

100

Fuel

Car

bon

into

em

issi

ons,

(%)

CO2COHCOHC

Simulations agree well with experiment

0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28Equivalence ratio

0

10

20

30

40

50

60

70

80

90

100

Fuel

Car

bon

into

em

issi

ons,

(%) Solid lines: experimental

Dashed lines: numerical

CO2COHCOHC

Our multi-zone model gives insight into the reduced combustion efficiency as equivalence ratio decreases

Complete Combustion

High CO

Fuel, IHC, CO

Unburned fuel

φ=0.26

φ=0.16

φ=0.10

φ=0.04

Our multi-zone model gives insight into the reduced combustion efficiency as equivalence ratio decreases

Complete Combustion

High CO

Fuel, IHC, CO

Unburned fuel

φ=0.26

φ=0.16

φ=0.10

φ=0.04

Our multi-zone model gives insight into the reduced combustion efficiency as equivalence ratio decreases

Complete Combustion

High CO

Fuel, IHC, CO

Unburned fuel

φ=0.26

φ=0.16

φ=0.10

φ=0.04

Our multi-zone model gives insight into the reduced combustion efficiency as equivalence ratio decreases

Complete Combustion

High CO

Fuel, IHC, CO

Unburned fuel

φ=0.26

φ=0.16

φ=0.10

φ=0.04

Outline

Through our collaborations we have applied these tools to a wide variety of industrially significant questions:– What effect does turbulence have on HCCI combustion?

• Completed study of Lund TD100 engine for low turbulence geometry, now conducting simulations on high turbulence geometry

– What are the low load limits to HCCI operation?• Study of HCCI low-load operation limits in Sandia engine

– Does mixing affect CO emissions in HCCI combustion?• Extended multi-zone model includes mixing effects – framework

for general tool to analyze of HCCI, PCCI, SCCI

• Analyzed post-combustion mixing and CO formation in HCCI engine

The original design of the multi-zone model is appropriate for modeling truly homogeneous HCCI combustion

Original Multi-zone Model: One-way mapping from Kivato Kinetic Solver

Enhancement to multi-zone model gives us the capability to handle stratified combustion (PCCI, SCCI)

Enhanced Model: Kinetic solver results are mapped back onto Kiva Grid

Kiva can now be used to account for mixing and heat transfer between zones for the whole cycle

The enhancements in the model allow us to move beyond “truly homogeneous” HCCI combustion

• Model is generally applicable to cases where heat release and mixing are weakly coupled

– PCCI = Premixed Charge Compression Ignition• High Internal EGR

– SCCI = Stratified Charge compression Ignition• Early Direct Injection

Accounting for mixing in multi-zone model yields much improved CO and HC emissions (SAE 2003-01-1821)

Experimental work

• What control methods are viable for multi-cylinder HCCI engines?– Designed and tested a generic control system for internal EGR

control of cylinder by cylinder variation in 4-cylinder engine– Implementing closed loop feedback control for cylinder-by-

cylinder phase balancing

Controlling cylinder-by-cylinder combustion timing is very important for multi-cylinder HCCI engines

20

25

30

35

40

45

50

55

-10 0 10 20 30Crank Angle (degrees)

Pres

sure

(bar

)Cylinder 1Cylinder 2Cylinder 3Cylinder 4

A generic, low cost surrogate to variable valve timing is being used for controlling cylinder to cylinder variations

Individual cylinder EGR Control by Exhaust Throttling

Surprising Exhaust Throttle Effects on start of combustion (SOC)

1. SOC delayed by backpressure of cylinder !

2. Constant fuel flow intake (non injected), and naturally aspirated air intake may explain SOC retardation.

3.0

4.0

5.0

6.0

7.0

-10.0 0.0 10.0 20.0

CAD

pres

sure

(10

bar

)

1 Throttled

Unthrottled

Cylinder 1 Response to Throttling

Surprising Exhaust Throttle Effects on SOC

Amazingly, throttling of other cylinders advances SOC of cylinder 1 !?!

3.0

4.0

5.0

6.0

7.0

-10.0 0.0 10.0 20.0

CAD

pres

sure

(10

bar

)

2 Throttled

1 Throttled

Unthrottled

Cylinder 1 Response to Throttling

Any Exhaust Throttle affects SOC in Cylinder 1

Backpressure of cylinders 3 and 4 also increases the SOC in cylinder 1

3.0

4.0

5.0

6.0

7.0

-10.0 0.0 10.0 20.0

CAD

pres

sure

(10

bar)

Cylinder 1 Response to Throttling

2 Throttled

1 Throttled

3 4

Unthrottled

Future analysis and experimental work will focus on cylinder interactions and how to control them