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The objective of this work was to improve the accuracy of the combustion speed estimation in rich fuel condition (φ ≻ 1.2) as in case of Gasoline Direct Injection (GDI) engine. During rich fuel mixture combustion, the accuracy of calculation of laminar burning velocity deteriorates because of not considering the flame stretch. In the present study, the unstable flame due to the imbalance of the mass diffusion and the temperature diffusion of the fuel (Lewis Number (Le) ≺ 1.0) was modeled. The laminar burning speed model was developed by considering the stretch. It was applied with three-dimensional combustion simulation tools together with the Universal Coherent Flamelet Model (UCFM), a flame propagation model. The model has shown the capability to reproduce the heat generation (heat release rate) at high accuracy in comparison with experimental data.

The objective of this work was to improve the accuracy of the combustion speed estimation in rich fuel condition (φ ≻ 1.2) as in case of Gasoline Direct Injection (GDI) engine. During rich fuel mixture combustion, the accuracy of calculation of laminar burning velocity deteriorates due to not considering the flame stretch. In the present study, the unstable flame was formed due to the imbalance of the mass diffusion and the temperature diffusion of the fuel (Lewis Number (Le) ≺1.0) was modeled. The laminar burning speed model was developed by considering the stretch. It was applied with three-dimensional combustion simulation tools together with the Universal Coherent Flamelet Model (UCFM), a flame propagation model. The model has shown the capability to reproduce the heat generation (heat release rate) at high accuracy in comparison with experimental data.

For diesel engine, lower compression ratio has been demanded to improve fuel consumption, exhaust emission and maximum power recently. However, low compression ratio engine might have combustion instability issues under cold temperature condition, especially just after engine started. As a first step of this study, cold temperature combustion was investigated by in-cylinder pressure analysis and it found out that higher heat release around top dead center, which was mainly contributed by pilot injection, was the key factor to improve engine speed fluctuation. For further understanding of combustion in cold condition, particularly mixture formation near a glow plug, 3D CFD simulation was applied. Specifically for this purpose, TI (Time-scale Interaction) combustion model has been developed for simulating combustion phenomena. This model was based on a reasonable combustion mode, taking into account the characteristic time scale of chemical reactions and turbulence eddy break-up.

Engine start timing of series hybrid system is important for quietness in the cabin and comfortable because its engine operation timing is not restricted by vehicle speed and acceleration. There is an opportunity to operate the engine without spoiling quietness if engine sounds could be covered by road noise. Discovering the correlation between road noise and variance of wheel angular acceleration using wheel speed sensor made it possible to estimate road noise. Engine start control based on this road noise estimation algorithm contributes to cabin quietness performance improvement as the result of less frequency of engine operating during smooth road driving.