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Homogeneous Ignition - Chemical Kinetic Studies for IC-Engine Applications

Amnéus, Per LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Beräkningar med detaljerade kemiska reaktionssytem, med uppemot 1500 kemiska reaktioner, har utförts på HCCI-motorer, en experimentell motortyp som bygger på homogen kompressionsantändning. Resultaten jämfördes med experimentella mätningar och visade att beräkningar med god noggrannhet kan utföras, men att antändingsprocessen är mycket känslig för även små variationer i temperatur, bränsleblandning, och eventuella felaktigheter i reaktionsmekanismen.



Den kemisk-kinetiska modellen kunde även kopplas till två olika motorsimuleringsverktyg. Dessa kombinerade beräkningsprogram visade sig vara ett väl fungerande analysverktyg för motorsystem.



Metoder för... (More)
Popular Abstract in Swedish

Beräkningar med detaljerade kemiska reaktionssytem, med uppemot 1500 kemiska reaktioner, har utförts på HCCI-motorer, en experimentell motortyp som bygger på homogen kompressionsantändning. Resultaten jämfördes med experimentella mätningar och visade att beräkningar med god noggrannhet kan utföras, men att antändingsprocessen är mycket känslig för även små variationer i temperatur, bränsleblandning, och eventuella felaktigheter i reaktionsmekanismen.



Den kemisk-kinetiska modellen kunde även kopplas till två olika motorsimuleringsverktyg. Dessa kombinerade beräkningsprogram visade sig vara ett väl fungerande analysverktyg för motorsystem.



Metoder för matematisk reduktion av reaktionmekanismer utvecklades, i syfte att korta beräkningstiderna. Två metoder testades; genering av skelettmekanismer med sensitivitetsanalys av hastighetskonstanterna kombinerat med analys av atomära flöden, respektive antagandet av kvasi-steady-state för kortlivade reaktionsintermediärer. Vardera metod fungerade relativt väl var för sig. Bägge metoderna i kombination förbättrade dock avsevärt potentialen för små avvikelser från den detaljerade mekanismen i kombination med drastiska minskningar i beräkningstider.



En detaljerad generell reaktionsmekanism för formaldehyd, metan och metanol utvecklades, med god noggrannhet vad gäller antändningstider för samtliga komponenter. En semi-detaljerad reaktionsmekanism för n-heptan/iso-oktan-blandingar utvecklades. Denna mekanism kombinerar goda noggrannhet i antändningsprediktioner med (för bränslet) korta beräkningstider. (Less)
Abstract
Calculations on a Homogeneous Charge Compression Ignition (HCCI) engine have been performed. Zero-dimensional models were used. The simplest model compressed the gas to auto-ignition, using temperature and pressure at a certain crank angle position obtained from engine experiments.



It was found that calculations with good agreement could be accomplished, if using correct temperature, pressure and air/fuel mixture composition. However, the calculations proved to be extremely sensitive to even small variations in temperature. Further, natural gas engine calculations showed a high sensitivity to the contents of higher hydrocarbons such as ethane, propane and butanes. The validity of the kinetic mechanism was also a crucial... (More)
Calculations on a Homogeneous Charge Compression Ignition (HCCI) engine have been performed. Zero-dimensional models were used. The simplest model compressed the gas to auto-ignition, using temperature and pressure at a certain crank angle position obtained from engine experiments.



It was found that calculations with good agreement could be accomplished, if using correct temperature, pressure and air/fuel mixture composition. However, the calculations proved to be extremely sensitive to even small variations in temperature. Further, natural gas engine calculations showed a high sensitivity to the contents of higher hydrocarbons such as ethane, propane and butanes. The validity of the kinetic mechanism was also a crucial factor. Due to the assumption of total homogeneity in the combustion chamber, a too rapid heat release was predicted.



Two interfaces were developed, coupling the chemical kinetics code to existing engine simulation tools. These combined kinetics calculations and engine simulations proved to be an efficient tool for HCCI-engine analyses.



Methods for mechanism reductions were developed, and implemented in the kinetic code. This was a stepwise procedure where the first part was to apply the quasi steady-state assumption (QSSA) on HCCI-calculations, where a measure of the species life-time was used to determine which species should be considered as steady-state species. The method showed a good agreement compared to the original mechanism, even for a relatively large degree of reduction.



Sensitivity analysis and reaction flow analysis was combined in a semi-automatic method to generate skeletal mechanisms. The skeletal mechanisms give a good agreement, but only for a limited degree of reduction. A fully automatic method for reduction over a selected range of physical parameters was developed. It combines the two methods by applying QSSA on an automatically generated skeletal mechanism. The suggested method showed good agreement and an excellent potential for future tailor made reaction mechanisms, using a detailed reaction mechanism as a basis.



A reaction mechanism for formaldehyde, methane and methanol was developed. The aim for this work was to produce a C1 mechanism of general characteristics, covering formaldehyde, methane, and possible methanol, giving correct species profiles for intermediate products. The mechanism was capable of accurately predicting ignition delays for formaldehyde and methane over a wide range, gave decent methanol auto-ignition prediction, and could further accurately predict the species profiles for formaldehyde but was not capable of calculating flame speeds for methane.



A semi-detailed reaction mechanism for Primary Reference Fuels, mixtures of iso-octane and n-heptane, was developed. The predictions of ignition delay times showed a good agreement to experiments. The mechanism proved to be numerically efficient compared to mechanisms of equivalent accuracy. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Morley, Chris
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Skeletal mechanism, Mechanism reduction, n-heptane, iso-octane, formaldehyde, methane, Motors and propulsion systems, Motorer, framdrivningssystem, Physics, Fysik, Detailed chemistry, Kinetic calculations, Engine knock, Homogeneous charge compression ignition, HCCI, Fysicumarkivet A:2002:Amnéus
pages
242 pages
publisher
Combustion Physics, Lund Institute of Technology
defense location
Sal F, Physics building
defense date
2001-12-12 14:15
external identifiers
  • other:ISRN: LUTFD2/TFCP--81--SE
ISSN
1102-8718
language
English
LU publication?
yes
id
24598bb3-a460-42b7-9844-386e1b776b7f (old id 465272)
date added to LUP
2007-09-28 09:15:58
date last changed
2016-09-19 08:44:54
@phdthesis{24598bb3-a460-42b7-9844-386e1b776b7f,
  abstract     = {Calculations on a Homogeneous Charge Compression Ignition (HCCI) engine have been performed. Zero-dimensional models were used. The simplest model compressed the gas to auto-ignition, using temperature and pressure at a certain crank angle position obtained from engine experiments.<br/><br>
<br/><br>
It was found that calculations with good agreement could be accomplished, if using correct temperature, pressure and air/fuel mixture composition. However, the calculations proved to be extremely sensitive to even small variations in temperature. Further, natural gas engine calculations showed a high sensitivity to the contents of higher hydrocarbons such as ethane, propane and butanes. The validity of the kinetic mechanism was also a crucial factor. Due to the assumption of total homogeneity in the combustion chamber, a too rapid heat release was predicted.<br/><br>
<br/><br>
Two interfaces were developed, coupling the chemical kinetics code to existing engine simulation tools. These combined kinetics calculations and engine simulations proved to be an efficient tool for HCCI-engine analyses.<br/><br>
<br/><br>
Methods for mechanism reductions were developed, and implemented in the kinetic code. This was a stepwise procedure where the first part was to apply the quasi steady-state assumption (QSSA) on HCCI-calculations, where a measure of the species life-time was used to determine which species should be considered as steady-state species. The method showed a good agreement compared to the original mechanism, even for a relatively large degree of reduction.<br/><br>
<br/><br>
Sensitivity analysis and reaction flow analysis was combined in a semi-automatic method to generate skeletal mechanisms. The skeletal mechanisms give a good agreement, but only for a limited degree of reduction. A fully automatic method for reduction over a selected range of physical parameters was developed. It combines the two methods by applying QSSA on an automatically generated skeletal mechanism. The suggested method showed good agreement and an excellent potential for future tailor made reaction mechanisms, using a detailed reaction mechanism as a basis.<br/><br>
<br/><br>
A reaction mechanism for formaldehyde, methane and methanol was developed. The aim for this work was to produce a C1 mechanism of general characteristics, covering formaldehyde, methane, and possible methanol, giving correct species profiles for intermediate products. The mechanism was capable of accurately predicting ignition delays for formaldehyde and methane over a wide range, gave decent methanol auto-ignition prediction, and could further accurately predict the species profiles for formaldehyde but was not capable of calculating flame speeds for methane.<br/><br>
<br/><br>
A semi-detailed reaction mechanism for Primary Reference Fuels, mixtures of iso-octane and n-heptane, was developed. The predictions of ignition delay times showed a good agreement to experiments. The mechanism proved to be numerically efficient compared to mechanisms of equivalent accuracy.},
  author       = {Amnéus, Per},
  issn         = {1102-8718},
  keyword      = {Skeletal mechanism,Mechanism reduction,n-heptane,iso-octane,formaldehyde,methane,Motors and propulsion systems,Motorer,framdrivningssystem,Physics,Fysik,Detailed chemistry,Kinetic calculations,Engine knock,Homogeneous charge compression ignition,HCCI,Fysicumarkivet A:2002:Amnéus},
  language     = {eng},
  pages        = {242},
  publisher    = {Combustion Physics, Lund Institute of Technology},
  school       = {Lund University},
  title        = {Homogeneous Ignition - Chemical Kinetic Studies for IC-Engine Applications},
  year         = {2002},
}