Modeling of HCCI and PCCI Combustion Processes

Dan Flowers, Salvador AcevesLawrence Livermore National Laboratory

Robert DibbleUniversity of California, Berkeley

Randy HesselUniversity of Wisconsin, Madison

Aristotelis BabajimopolousUniversity of Michigan

Work performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.

Project Overview: HCCI Engines have potential for High Efficiency and Low EmissionsHomogenous Charge Compression Ignition (HCCI)

engines have many potential advantages:– Very Low NOx Emissions– Very Low Particulate Emissions– High Efficiency– Lower Cost

We apply chemical kinetic modeling and experiments towards solving technical barriers of HCCI engines:– Combustion timing measurement and control– Cylinder-by-cylinder combustion timing control– Startup– Fuel air ratio measurement and control– Low Power Density– Hydrocarbon and CO emissions

Approach: Fundamental and practical understanding of HCCI by judicious use of modeling and experiments

• Develop numerical tools that predict HCCI combustion with complex fuels in reasonable computational time (hours and days, not weeks and months)

High Resolution CFD

H3C

C CH3

H2C

H3C

CH

CH2O

.O

H2C

C CH3

H2C

H3C

CH

H3C

O

HOH3C

CH

H2C

H3CCH

H2C

O O.

O

OH

Additive 1

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H2C

C CH3

H2C

H3C

CH2

O

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HO

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C

H3C

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CH3 O.

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H3C

CH C

H3CCH2

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O

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OH

HC

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HO

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O

OHO

O.

H3C

C CH3

H2C

H3C

C

H3CO

CH3 OH

Additive 204

Detailed Chemistry

Engine Experiments

Fundamental Understanding

+Design

Guidance

Objective: Modeling and experiments applied to technical barriers towards practical HCCI engines Applying multizone detailed chemical kinetics models to

understanding fundamentals of HCCI operation

Extending and applying multizone modeling tools to handle non-homogeneous, but “HCCI-like,”combustion regimes: PCCI, SCCI

Modeling and experiments to understand fundamental and practical issues in HCCI– HCCI with binary fuel mixtures using Carbon-14 tracing– Studying chemi-ionization as a practical means for combustion

timing measurement

We have long standing partnerships with industry and academia

• Cummins– Currently involved in CRADA partnership– Previous CRADA produced 2 joint papers

• Caterpillar– Providing experimental support– Close collaboration on natural gas HCCI

• Sandia National Laboratories– Detailed analysis of experimental data, paper

• Lund Institute of Technology– 3 joint papers, collaboration on analysis

• University of Wisconsin– joint work on KIVA analysis– 6 joint papers

• UC Berkeley– joint experimental and numerical work, >20 joint

papers– graduate students obtaining degrees on HCCI

• U Michigan– PhD research conducted at LLNL

Our experiments and modeling advance both practical and fundamental understanding of HCCI and PCCI• Characterized the role of turbulence on HCCI

combustion through multizone modeling• Completed development of Fully Integrated KIVA3V-

multizone (KIVA3V-MZ) model for simulation of HCCI and PCCI combustion

• Parallelized KIVA3V-multizone (KIVA3V-MZ-MPI) chemistry solver to significantly reduce computational time

• Developed rugged and low cost combustion timing sensor for HCCI combustion through ion sensing

• Investigated fuel and additive effects on HCCI combustion using C14 tracing of emission sources

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

Lower turbulence piston crown

Higher turbulence piston crown

Experiments show longer burn duration for higher turbulence geometry

Our hypothesis: Chemistry timescales are far too rapid to be affected by local turbulence timescales, therefore turbulence plays only an indirect role through heat transfer

Our Multi-zone approach has proven accurate for HCCI combustion with wide range of fuels and engine geometries

KIVA3V is run until a specific Transition point

Multi-zone HCT model used for simulating cycle after transition point

KIVA Temps mapped one-wayonto multizone HCT

High resolution CFD with detailed chemistry at every grid point exceeds capability of today’s computers• Possible Approaches:

– Few grid points for CFD and Chemistry– Many grid points for CFD, a few grid points for chemistry (Our approach)

- works when chemistry and turbulence weakly interact ( e.g. HCCI)

1 Hour

1 Month

1 Decade

1 Day

KineticsCFD

Engine Cycle Simulation(single processor)Axisymmetric CFD grid~200 chemical species

Engine Cycle Simulation(single processor)Axisymmetric CFD grid~200 chemical species 1 Year

We have analyzed HCCI operation both low and high turbulence geometries using the multizone approach

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

Kiva simulations show the flow pushed into the square bowl near TDC with high turbulence geometry

Very little change in swirl velocity occurs with flat-top piston geometry during compression

Flat piston Square bowl piston

Substantial recirculation occurs in square-bowl piston, very little with flat-top

Flat piston Square bowl piston

Higher turbulence yields more heat transfer and broader temperature distribution within the cylinder

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temperature, K

mas

s fra

ctio

n at

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pera

ture

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s

disc, peak heat release at 3° ATDCsquare, peak heat release at 3° ATDC

Our multizone model shows that broader temperature distribution explains the lengthening of the burn duration

Heat release rate, flat piston Heat release rate, square bowl

Conclusion: HCCI is dominated by chemical kinetics, turbulence plays an indirect role through heat transfer

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Burn

dur

atio

n, C

AD

crank angle for peak heat release rate

solid line: experimental

squaredisc

dotted line: numerical

Our Multi-zone approach has proven accurate for HCCI combustion with wide range of fuels and engine geometries

But great interest in partially stratified “HCCI” for better control and higher power output (PCCI, SCCI)

KIVA is run until a specific transition point

Multi-zone HCT model used for simulating cycle after transition point

KIVA Temps mapped one-way onto multizoneHCT

We extend this model to map between CFD and Multi-zone detailed kinetic solver throughout the engine cycle

Fully Integrated KIVA and Multi-zone model (KIVA-MZ)High resolution CFD solver handles mixing, advection and diffusion (>10K cells)

Solutions are mapped back and forth between solvers throughout the cycle

Chemistry handled by multizone detailed kinetics solver (10-100 zones)

Significant reduction in computational time with CFD+multizone approach, but…This approach still requires 50-100 chemistry zones – Still

computationally intensive, esp. with big mechanisms

Multi-zone model is readily parallelized, parallel multizonechemistry solver now implemented within KIVA3V, yields near linear speedup with number of processors

Fully integrated KIVA3V-MZ-MPI handles chemistry part of simulation in parallelFluid mechanics still handled with single processor

Chemistry handled with additional processors, chemistry speedup scales almost linearly with number of processors (up to ~ number of zones)

Process 0

Fluid mechanics step

Processes 1 – (N-1)

Zone1 Zone 2 Zone 3 Zone M

High resolution CFD with detailed chemistry at every grid point exceeds capability of today’s computers• Possible Approaches:

– Few grid points for CFD and Chemistry– Many grid points for CFD, a few grid points for chemistry (Our approach)

- works when chemistry and turbulence weakly interact ( e.g. HCCI)

1 Hour

1 Month

1 Decade

1 Day

KineticsCFD

Engine Cycle Simulation(single processor)Axisymmetric CFD grid~200 chemical species

Engine Cycle Simulation(single processor)Axisymmetric CFD grid~200 chemical species 1 Year

Parallelization can shift kinetics cost dramatically lower

Simulations were conducted to analyze Isooctane HCCI in the Sandia Engine (Experiments SAE 2003-01-0752)

5.88 mm(0.2314 in)

5.23 mm(0.206 in)

9.01 mm(0.355 in)

0.305 mm(0.0120 in)

102 mm(4.02 in)

Our fully integrated KIVA3V-MZ-MPI solver predicts pressure very well compared to Sandia experiments

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-10 -5 0 5 10 15 20Crank Angle, Degrees

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sure

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Phi=0.26 ExperimentPhi=0.20 ExperimentPhi=0.16 ExperimentPhi=0.10 ExperimentPhi=0.26 SimulationPhi=0.20 SimulationPhi=0.16 SimulationPhi=0.10 Simulation

KIVA3V-MZ-MPI emissions predictions are also in good agreement with the experiment

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0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26phi

Fuel

Car

bon

Into

Em

issi

ons

%Fuel C into CO [%] Experiment

%Fuel C into CO2 [%] Experiment

%Fuel C into HC [%] Experiment

%Fuel into OHC [%] Experiment

%Fuel C into HC [%] Simulation

%Fuel into OHC [%] Simulation

%Fuel C into CO [%] Simulation

%Fuel C into CO2 [%] Simulation

Strength of the fully integrated KIVA3V-MZ-MPI solver is simulation of non-homogenous HCCI-like processesUsing validated cases as a baseline, simulations

conducted to investigate imposition of stratification on combustion

High Stratification

Mild Stratification

Uniformφ

Comparison of equivalence ratio at 35 degrees BTDC (φ=0.26 Overall)

HC and OHC lower with increased stratification, CO higher for some higher stratification conditionsConsistent with experimental observations for early direct

injection engines

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or O

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steep (HC)shallow (HC)uniform (HC)steep (OHC)shallow (OHC)uniform (OHC)

NOx emissions increase due to higher local equivalence ratio with increased stratification

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KIVA3V-MZ-MPI simulation is currently being used to investigate PCCI with early direct injectionEarly Direct injection

using KIVA spray model for diesel fuel

100 zone (with 100 processors) simulation with n-heptane diesel fuel surrogate

Summary: We continue to use our simulation capabilities to complement HCCI R&D in Industry, Nat Labs, Universities

• We now have the tools to computationally optimize the geometry, and fuel-air-EGR distributions in HCCI and HCCI-like engines

• KIVA3V-MZ-MPI is a computationally efficient and accurate tool coupling fluid mechanics and detailed chemical kinetics for prediction HCCI

• We have extended multizone tools to handle non-homogeneous direct injected PCCI regimes

• Experiments, numerical modeling, and other unique capabilities applied to fundamental and practical issues of HCCI

Future Plans: We will continue to develop tools and analysis to guide HCCI engine design• Continue applying KIVA3V-MZ-MPI to early direct liquid

fuel injection PCCI

• Apply modeling to support optical engine PCCI experiments (Dec, Steeper)

• Investigate non-homogeneous engine operation towards higher load and lower HC and CO emissions

• Investigate effects of fuels and fuel mixtures on PCCI and HCCI operation

• Study practical strategies of combustion timing measurement and control for multi-cylinder engines

Recent and Upcoming Publications (1)

1) “Analysis of the Effect of Geometry Generated Turbulence on HCCI Combustion by Multi-Zone Modeling” SAE Paper 2005-01-2134.

Collaboration: Lund Inst., U WisconsinHighlights: Detailed study of Role of Turbulence in HCCI combustion

2) “A Fully Integrated CFD and Multi-zone Model with Detailed Chemical Kinetics for the Simulation of PCCI Engines”International Journal of Engine Research (in press).

Collaboration: U Michigan, U WisconsinHighlights: Development of approach for Fully Integrated Kiva-Multi-zone

Detailed chemical kinetics code for simulation of HCCI and PCCI engines

3) “Effect of the Di-Tertiary Butyl Peroxide (DTBP) additive on HCCI Combustion of Fuel Blends of Ethanol and Diethyl Ether” SAE Paper 2005-01-2135.

Collaboration: UC Berkeley, CAMS(LLNL)Highlights: Carbon 14 tracing investigating role of ignition enhancing

additives on HCCI combustion with fuel mixtures.

Recent and Upcoming Publications (2)

4) “Experimental and Numerical Investigation of Effect of Fuel on Ion Sensor Signal to Determine Combustion Timing in HCCI Engines,”International Journal of Engine Research (in press).

Collaboration: UC BerkeleyHighlights: Developed ion formation model for HCCI engines for multiple

fuels, verified model with experiments

5) “EGR effect on Ion Signal in HCCI Engines,” SAE 2005-01-2126.Collaboration: UC BerkeleyHighlights: Experimental verification of ion formation chemical kinetics for

HCCI with high EGR, for conditions ranging from very lean to slightly rich conditions

6) “Combustion Timing in HCCI Engines Determined by Ion-Sensor: Experimental and Kinetic Modeling,” 30th International Symposium on Combustion.

Collaboration: UC Berkeley, U HeidelbergHighlights: First application and experimental verification of ion chemical

kinetic mechanism applied to HCCI engines.

Recent and Upcoming Publications (3)

7) “Investigation of HCCI Combustion of Diethyl Ether and Ethanol Mixtures Using Carbon 14 Tracing and Numerical Simulations,”30th International Symposium on Combustion.

Collaboration: UC Berkeley, CAMS(LLNL)Highlights: Carbon 14 tracing used to investigate sources of emissions

from dual component fuel blends in HCCI engines

8) “Spatial Analysis of Emissions Sources for HCCI Combustion atLow Loads Using a Multi-Zone Model,” SAE Paper 2004-01-1910.Collaboration: SNL, U Wisconsin, UC BerkeleyHighlights: Detailed chemical kinetic analysis of geometry dependent

emissions from an HCCI engine at low loads

9) “Analysis of Homogeneous Charge Compression Ignition (HCCI) Engines for Cogeneration Applications,” Proceedings of the ASME Advanced Energy Systems Division, 2004

Collaboration: Oregon State UniversityHighlights: evaluation of the multiple advantages of HCCI for CHP

Recent and Upcoming Publications (4)

10) “Thermal Management for 6-Cylinder HCCI Engine: Low Cost, High Efficiency, Ultra-Low NOx Power Generation, Proceedings of the ASME Internal Combustion Engine Division, May 2004

Collaboration: UC BerkeleyHighlights: Characterization of HCCI combustion for stationary power

11) “Improving Ethanol Life Cycle Energy Efficiency by Direct Combustion of Wet Ethanol in HCCI engines,” Proceedings of the ASME Advanced Energy Systems Division

Highlights: how HCCI combustion of wet ethanol can greatly improve energy balance for ethanol production

12) “Source Apportionment of Particulate Matter from a Diesel Pilot-Ignited Natural Gas Fuelled Heavy Duty DI Engine, SAE Paper 2005-01-2034

Collaboration: University of British ColumbiaHighlights: C-14 analysis for identification of source of pollutants in a dual

fuel engine

Other collaborative activities

• Ongoing participation at MOU meetings with vehicle and engine manufacturers

• Invited presentation at SAE HCCI symposium• Invited presentation at ECI Lean Combustion

Technology II workshop• Several publications with National Laboratories and

Universities in US and abroad:– SAE– The Combustion Institute– International Journal of Engine Research