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|Title: ||CFD modelling of natural gas combustion in spark ignited engines|
|Authors: ||Palipana, Aruna S.|
|Issue Date: ||2000|
|Publisher: ||© Aruna Susantha Palipana|
|Abstract: ||Natural gas is gaining popularity as a fuel for automobile applications. In
order to procure all the benefits of using natural gas, dedicated engines optimised for this
fuel are needed. It is necessary to validate multi-dimensional models of combustion of
natural gas in SI engines as such models provide a powerful tool in designing engines
and optimising them for this fuel and for studying the emission of pollutants.
The multi-dimensional CFD code, KN A-IT, has been used in this study,
with necessary modifications and additions. Several combustion models commonly used
for SI engine modelling in CFD environments were evaluated. It was concluded that
flamelet combustion models are more suitable for engine combustion modelling as
engine combustion, in almost all cases, lies within the flamelet regime of combustion.
One such flamelet model, the Fractal Flame Model (FFM), was improved, implemented
and validated for simulating the turbulent phase of the combustion process in a spark
ignited, natural gas fuelled engine. The model validation was done by comparing predictions
with experimental data for the base line case. This validated model was then used to study
the effects of engine operating parameters and combustion chamber geometry on engine
performance and emissions thus providing a suitable analytical background for the
designing of dedicated engines optimised for natural gas. This parametric study was
performed over a range of air/fuel ratios, with ignition timing, compression ratio and
engine speed as the variable parameters. The trends predicted were used to assess the
predictive capabilities of the FFM.
Eddy break up model (EBUM) was used to compare the predictions by the
FFM and these comparisons indicated that the FFM resulted in better agreement with
experiments. The predicted trends of engine performance and pollutant formation with
the FFM agree well with those found in the literature. This indicates the strength of the
FFM as a combustion model for natural gas fuelled SI engines.
The effects of the combustion chamber geometry and exhaust gas
recirculation on engine performance and pollutant formation were numerically studied
and the trends obtained agree with experimental data available. The Renormalisation
Group Theory (RNG) k-ε turbulence model was compared with the standard k-ε model
and no significant effect on results was found.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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