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«Chemical kinetics modelling study on fuel autoignition in internal combustion engines This item was submitted to Loughborough University's ...»

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Loughborough University

Institutional Repository

Chemical kinetics modelling

study on fuel autoignition in

internal combustion engines

This item was submitted to Loughborough University's Institutional Repository

by the/an author.

Additional Information:

• A Doctoral Thesis. Submitted in partial fulllment of the requirements

for the award of Doctor of Philosophy of Loughborough University.

https://dspace.lboro.ac.uk/2134/6533

Metadata Record:

c Zhen Liu

Publisher:

Please cite the published version.

This item was submitted to Loughborough’s Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.

For the full text of this licence, please go to:

http://creativecommons.org/licenses/by-nc-nd/2.5/ Chemical Kinetics Modelling Study on Fuel Autoignition in Internal Combustion Engines by Zhen Liu A Doctoral Thesis submitted in partial fulfilment of the requirements for the award of Degree of Doctor of Philosophy of Loughborough University July 2010 © by Zhen Liu 2010 Abstract Abstract Chemical kinetics has been widely acknowledged as a fundamental theory in analysis of chemical processes and the corresponding reaction outputs and rates.

The study and application of chemical kinetics thus provide a simulation tool to predict many characteristics a chemical process. Oxidation of hydrocarbon fuels applied in internal combustion engines is a complex chemical process involving a great number of a series of chained reaction steps and intermediate and simultaneous species. Symbolic and Numerical description of such a chemical process leads to the development and application of chemical kinetics models. The up-to-date application of chemical kinetics models is to the simulation of autoignition process in internal combustion engines.

Multi-zone thermodynamic combustion modelling has been regarded as a functional simulation approach to studying combustion process in IC engines as a decent compromise between computation accuracy and efficiency. Integration of chemical kinetics models into multi-zone models is therefore a potential modelling method to investigate the chemical and physical processes of autoignition in engine combustion.

This research work has been therefore concerned with the development, validation and application of multi-zone chemical kinetic engine models in the simulation of autoignition driven combustion in SI and HCCI engines. The contribution of this work is primarily made to establish a mathematical model based on the underlying physical and chemical principles of autoignition of the fuel-air mixture in SI and HCCI engines. Then, a computer code package has been developed to numerically solve the model. The derived model aims at improving the understanding of autoignition behaviour under engine-like conditions and providing an investigative tool to autoignition characteristics. Furthermore, as part of the ongoing program in the research of free piston engines, the results of this work will significantly aid in the

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investigation and simulation of the constant volume autoignition applied in free piston engines.

Keywords: Autoignition, Knock, SI, HCCI, Chemical Kinetics, Multi-zone, Modelling, IEGR, LUCKS, Mixing, DVODE

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Figure List Figure 2-1: Comparison of normal (a) and abnormal (b and c) combustion phenomenon in SI engines [2]

Figure 2-2: Schematic of combustion process with and without knock [6]................ 10 Figure 2-3: Typical SI engine envelope of end gas temperature and pressure histories leading up to the point of knock [26].

Figure 2-4: Branching pathways for hydrocarbon oxidation at low and intermediate temperatures [27].

Figure 2-5: Pressure history during the two-stage autoignition [30]

Figure 2-6: Molecular structures of n-heptane (a) and iso-octane (b).

Figure 3-1: Comparison of SI, HCCI and CI combustion engines.

Figure 3-2: The depiction of the positive (left) and the negative valve (right) overlaps;

EC: Exhaust valve closing and IO: intake valve opening.

Figure 3-3: Typical cylinder pressure vs. crank angle showing injecting timing windows [105].

Figure 3-4: Interaction between the adiabatic core and the boundary layer [132].... 53 Figure 3-5: A Schematic drawing of a Multi-Zone model showing the Layout of the Different Zones [133]

Figure 3-6: Geometric description of the multi-zone model proposed by Komninos et al [131].

Figure 3-7: Distribution of EGR and mixture temperature over zones in the multi-zone model developed by Orlandini et al [136].

Figure 4-1: Major branches of n-heptane oxidation [6].

Figure 4-2: The four different sites for H abstraction in n-heptane.

Figure 4-3: Reaction mechanism of isomerisation of C 7 H 15 OO.

 Figure 4-4: Reaction mechanism of isomerisation of OOC H14OOH.

7 Figure 4-5: Major reaction branches of iso-octane oxidation [6].

Figure 4-6: Different types of CH groups in n-heptane (left) and iso-octane (right).. 78 Figure 4-7: Different transition rings for internal H abstraction in n-heptane and isooctane





IIIFigure List

Figure 4-8: Reduced chemistry for oxidation of n-heptane and iso-octane mixtures [154]

Figure 4-9: Structure of degenerate chain branching mechanism of a skeletal model.

Figure 4-10: The skeletal chemical kinetics model of Li et al [178]

Figure 5-1: Example of instability encountered in integrating a stiff equation (schematic). Here it is supposed that the equation has two solutions, shown as solid and dashed lines. Although the initial conditions are such as to give the solid solution, the stability of the integration (shown as the unstable dotted sequence of segments) is determined by the more rapidly varying dashed solution, even after that solution has effectively died away to zero. Implicit integration methods are the cure [183].

Figure 6-1: The generic structure of the LUCKS code package.

Figure 6-2: The flowchart of the structure of the main program of LUCKS_HCCI and LUCKS_SI

Figure 7-1: Three-zone combustion chamber.

Figure 7-2: Calculated knock position and peak pressure vs. Enhancing Factors in R6 and R18.

Figure 7-3: Calculated knock intensity and combustion duration vs. Enhancing Factors in R6 and R18.

Figure 7-4: The structure of the LUCKS_SI program.

Figure 7-5: Knock position on a typical measured pressure trace.

Figure 7-6: Zoom-in image from Figure 7-5 to schematically express the definition of K ; tg  dPn / d and tg  dP 1 / d

n Figure 7-7: Comparison of the pressure traces between knocking cycles (top) and non-knocking cycles (bottom) extracted from the same set of recorded data

Figure 7-8: Knock intensity.vs. knock positions of the identified knocking cycles the fitted 3rd order polynomial function curve

Figure 7-9: Calculated and measured in-cylinder pressure under non-knocking conditions

Figure 7-10: Comparison of knock characteristics between calculated and measured data. (a): peak pressure (b): knock intensity (c): knock onset................ 139 Figure 7-11: Calculated in-cylinder pressure at various AFR.

Figure 7-12: Calculated and measured peak pressure at various AFR.................. 140 Figure 7-13: Calculated and measured knock onset position and knock intensity at various AFR

Figure 7-14: Comparison of calculated and measured knock onset positions in respect of RPM

Figure 7-15: Comparison of calculated and measured peak pressures in respect of RPM

Figure 7-16: Comparison of calculated and measured knock intensity in respect of

IVFigure List

RPM

Figure 7-17: MFB with and without unburned mixture autoignition.

Figure 7-18: Calculated knock onset positions and peak pressures in respect of intake pressure

Figure 7-19: Calculated knock intensity and combustion durations in respect of intake pressure

Figure 7-20: Calculated knock onset positions and peak pressures in respect of spark timings

Figure 7-21: Calculated knock intensity and combustion durations in respect of sparking timings

Figure 8-1: Zone configuration

Figure 8-2: Zone fraction distribution in a Gaussian-like shape

Figure 8-3: Influence of the additive sub-mechanism on the main combustion characters.

Figure 8-4: The flowchart of numerical procedures in Multi-Zone HCCI engine Simulation.

Figure 8-5: Calculated IEGR fraction, IEGR temperature and mixture temperature for each zone at 58% IEGR.

Figure 8-6: The general principle of the valve timing strategy.

Figure 8-7: Zone volume and cylinder volume in respect of crank angle................ 163 Figure 8-8: Zone pressure and average cylinder pressure (Refer to Figure 8-9 for an enlarged view)

Figure 8-9: Zone pressure and average cylinder pressure – the enlarged image of Figure 8-8.

Figure 8-10: Zone temperature and average cylinder temperature.

Figure 8-11: Zone mass histories in respect of crank angle.

Figure 8-12: Comparison of the calculated pressure curve with experimental results at 58% IEGR.

Figure 8-13: Comparison of the calculated pressure curve with experimental results at 50% IEGR.

Figure 8-14: Comparison of calculated and measured peak pressure and peak pressure position at various IEGR.

Figure 8-15: CO mole fraction history for each zone against crank angle at 58 % IEGR.

Figure 8-16: In-cylinder CO history against crank angle at 58 % IEGR.................. 170 Figure 8-17: Comparison of the calculated CO emission with the experimental results at various IEGR

Figure 8-18: HC mole fraction histories for each zone against crank angle at 58 % IEGR.

Figure 8-19: In-cylinder HC history against crank angle at 58 % IEGR.................. 172 Figure 8-20: Comparison of the calculated HC emission with the experimental results

VFigure List

at various IEGR

Figure 8-21: Calculated average in-cylinder temperature at various IEGR levels... 174 Figure 8-22: NOX mole fraction histories for each zone against crank angle at 58 % IEGR

Figure 8-23: In-cylinder NOX histories against crank angle at 58 % IEGR.............. 175 Figure 8-24: Comparison of the calculated NOX emission with the experimental results at various IEGR

Figure A-1: Pictorial comparison of CI, SI and HCCI engines.

Figure A-2: Working principle of a four-stroke engine [219].

Figure A-3: Working principle of a two-stroke engine [220].

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Table List Table 4-1: Typical Composition of Gasoline [150].

Table 4-2: Categorization of chemical kinetics models [6]

Table 4-3: A proposed global kinetics model combining a low temperature submechanism with a high temperature sub-mechanism [6].

Table 6-1: Definitions and conversion factors of CGS units relevant to SI units..... 120 Table 7-1: Engine specification.

Table 8-1: Engine parameters and operating conditions

Table A-1: Comparison of SI, CI and HCCI combustion processes

Table A-2: Classification of IC engine

Table A-3: Primary sources for hydrocarbon emissions in SI engines [217]........... 190 Table A-4: Classification of fuels used in IC engines [216]

Table A-5 Classification of methods of mixture generation

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Dedication This thesis is what it is today because of a few special people, and I would like to thank them for everything they have done in support my accomplishment of the thesis. First and foremost, to Professor Rui Chen, my supervisor who has been the most respectable master and friend in my life, I cannot fully express my gratitude for his care, faith, and superb guidance.

My gratitude especially to my aunts and uncles who have supported and had faith in me, without them, I would not have been typing this work in English.

Thank you especial to my dearest wife, Shanshan, who believed this work from the start and gives her full heart and soul to our life.

To my colleagues and friends, Pratap Rama, Paul Osei-Owusu and Anna Liu, for their help, kindness and trust, I am not able to be grateful enough.

I would be remiss and reproved if I did not mention the two extraordinary couples who have been of paramount importance in my life: first, my parents who are forever the best parents in the world for me and my parents-in-law, who treat me like a beloved son.

Last but not the least, lots of thanks to those friends and relatives whose name are not mentioned in this dedication, their help, understanding, and faith is considerably important.

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CHEMKIN Chemical Kinetics Modelling Code FLUENT Commercial CFD code KIVA Open-source CFD code for engine modelling SENKIN Closed-Volume, Gas-Phase Chemistry Code DVODE Double-precision Variable-coefficient Ordinary Differential Equation Solver LUCKS Loughborough University Chemical Kinetic Simulation Arabic Symbols

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Publications The following publications have been achieved in relation to this research.

Zhen, Liu and Chen, Rui.; Multi-Zone Kinetic Model of Controlled Auto Ignition Combustion, SAE World Congress & Exhibition, April 2009, Detroit, MI, USA. SAE 2009-01-0673 Zhen, Liu and Chen, Rui (2009) 'A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation', Combustion Science and Technology, 181:6, 828-852

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3.3.1.2 In Comparison to CI engines

3.3.1.3 Additional advantages

3.3.1.4 Summary

3.3.2 Challenges of HCCI combustion

3.3.2.1 Hydrocarbons and Carbon Monoxide (HC and CO)

3.3.2.2 Control of Combustion Phasing and Rate

3.3.2.3 Operation Range

3.3.2.4 Homogeneous Mixture Preparation

3.3.2.5 Cold-Start Capability

3.3.2.6 Summary

3.4 Research Work in HCCI Engines

3.4.1 Fundamental Studies

3.4.2 Technologies in HCCI engine

3.4.2.1 Variable Compression Ratio (VCR)

3.4.2.2 Variable Valve Timing (VVT)

3.4.2.3 Supercharging and Turbocharging

3.4.2.4 Stratified Charge



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