The development of an enhanced autoignition sub-model for use in CFD combustion simulations

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dc.contributor.advisorYates, Andrewen_ZA
dc.contributor.advisorMeyer, Chrisen_ZA
dc.contributor.authorCox, Ryanen_ZA
dc.date.accessioned2014-07-31T11:30:29Z
dc.date.available2014-07-31T11:30:29Z
dc.date.issued2006en_ZA
dc.descriptionIncludes bibliographical references.
dc.description.abstractWith the ever increasing pressure to manufacture more efficient engines that produce lowerexhaust emissions, there is a corresponding need for a greater understanding of the combustion processes within these engines. Specifically, it is the interaction between the fuel and the engine that represents one of the greatest research challenges. As the systemsbecome increasingly sophisticated, the fuel companies are experiencing an increased demand for high specification fuels with tighter tolerances. Now, more than ever, the fueldesign and engine design need to work as one integrated system to meet these expectations. In this project, an attempt was made to produce a computationally efficient mathematical model of the fuel ignition characteristics that could be used in a CFD simulation of an internal combustion engine or any other generic combustion system. The validation of the model provided useful insight into the need for good quality experimental data for the fuels of interest, highlighting the need for pure ignition delay curves without engine effects, which is a limitation of many of the current models. When modelling a single fuel droplet, the importance of the temperature profile in the vicinity of the evaporating particle was clearly illustrated, as well as the variation in the local air/fuel ratio. These effects were shown to playoff against each other - the centre of the droplet being coldest and hence yielding a longer ignition delay while, at the same time, the high equivalence ratio near the centre had the effect of shortening the ignition delay. Using a simple, two dimensional model and using n-Heptane as the fuel, a realistic prediction of the overall ignition delay was obtained. More importantly, the critical zone of the initial auto ignition was identified. These simulations show how this model can be used in an environment that exhibits both gradients of temperature and equivalence ratio. It also shows the importance of including such in-homogeneities when creating engine models that include fuel injection. This approach can easily be extended into any type of combustion simulation involving fuel droplets where local temperature and equivalence ratios have a controlling effect on the ignition. Some recommendations for future work include the modelling of the IQT™ with the possibility of reconciling the ignition delay of the IQT™ and the cetane test.en_ZA
dc.identifier.apacitationCox, R. (2006). <i>The development of an enhanced autoignition sub-model for use in CFD combustion simulations</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering. Retrieved from http://hdl.handle.net/11427/5570en_ZA
dc.identifier.chicagocitationCox, Ryan. <i>"The development of an enhanced autoignition sub-model for use in CFD combustion simulations."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering, 2006. http://hdl.handle.net/11427/5570en_ZA
dc.identifier.citationCox, R. 2006. The development of an enhanced autoignition sub-model for use in CFD combustion simulations. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Cox, Ryan AB - With the ever increasing pressure to manufacture more efficient engines that produce lowerexhaust emissions, there is a corresponding need for a greater understanding of the combustion processes within these engines. Specifically, it is the interaction between the fuel and the engine that represents one of the greatest research challenges. As the systemsbecome increasingly sophisticated, the fuel companies are experiencing an increased demand for high specification fuels with tighter tolerances. Now, more than ever, the fueldesign and engine design need to work as one integrated system to meet these expectations. In this project, an attempt was made to produce a computationally efficient mathematical model of the fuel ignition characteristics that could be used in a CFD simulation of an internal combustion engine or any other generic combustion system. The validation of the model provided useful insight into the need for good quality experimental data for the fuels of interest, highlighting the need for pure ignition delay curves without engine effects, which is a limitation of many of the current models. When modelling a single fuel droplet, the importance of the temperature profile in the vicinity of the evaporating particle was clearly illustrated, as well as the variation in the local air/fuel ratio. These effects were shown to playoff against each other - the centre of the droplet being coldest and hence yielding a longer ignition delay while, at the same time, the high equivalence ratio near the centre had the effect of shortening the ignition delay. Using a simple, two dimensional model and using n-Heptane as the fuel, a realistic prediction of the overall ignition delay was obtained. More importantly, the critical zone of the initial auto ignition was identified. These simulations show how this model can be used in an environment that exhibits both gradients of temperature and equivalence ratio. It also shows the importance of including such in-homogeneities when creating engine models that include fuel injection. This approach can easily be extended into any type of combustion simulation involving fuel droplets where local temperature and equivalence ratios have a controlling effect on the ignition. Some recommendations for future work include the modelling of the IQT™ with the possibility of reconciling the ignition delay of the IQT™ and the cetane test. DA - 2006 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2006 T1 - The development of an enhanced autoignition sub-model for use in CFD combustion simulations TI - The development of an enhanced autoignition sub-model for use in CFD combustion simulations UR - http://hdl.handle.net/11427/5570 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/5570
dc.identifier.vancouvercitationCox R. The development of an enhanced autoignition sub-model for use in CFD combustion simulations. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering, 2006 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/5570en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Mechanical Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMechanical Engineeringen_ZA
dc.titleThe development of an enhanced autoignition sub-model for use in CFD combustion simulationsen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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