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Quasi-dimensional combustion model of knock has been developed to predict knock occurrence in heavy<br/> LPG single cylinder engines. BOOST was applied to predict the mass flow into and out of engine. Reduced<br/> kinetic models are used to simulate auto-ignition in the unburned gas region. The model shows the expected<br/> tendency with the variations of intake port system, spark timing, engine speed.
The characteristics of spray. auto-ignition and combustion process of DME (Dimetyl ether) were investigated by 3-D simulation in a combustion vessel under high temperature and pressure conditions and engine conditions. Spray impingement and non-premixed combustion model were developed and incorporated into the computational fluid dynamics code, STAR-CD. Peng-Robinson EOS was introduced to calculate the evaporating rate of DME droplets in high pressure conditions. A Laminar flamelet concept was used to simulate non-premixed combustion. As the chemical mechanism of DME, a skeletal chemical kinetics mechanism which consists of 28 species and 45 reactions was derived by approximation of the detailed mechanism. In comparison with experimental data, the flamelet-concepted combustion model predicted the essential feature of the combustion process and the autoignition characteristics of the DME spray reasonably well for the various initial conditions. Also, the combustion process of the DI engine fueled by DME was simulated and verified by experiment data.
Ignition delay of second injection of HSDI diesel engine was usually much shorter than that of first injection. It is due to the interaction between radicals generated during the combustion process, and mixed gas of second injection. In this paper, To analyze combustion phenomena of multiple injection mode in HSDI diesel engine effectively, two-dimensional flamelet combustion model was modified. To reduce calculation time, two-dimensional flamelet equations were only applied near stoichiometric region. If this region was ignited, species and temperature of other region were changed to the steady-state solutions of one dimensional flamelet equations. By this method calculation time for solving flamelet equations was reduced to 20 percents, thought the results were almost same. Modified flamelet combustion model was coupled to commercial CFD code interactively using user subroutine.
New reduced chemical kinetic mechanism for prediction of autoignition process of HSDI diesel engine was investigated. For precise prediction of the ignition characteristics of diesel fuel, mechanism coefficients were fitted by the experimental results of ignition delay of diesel spray in a constant volume vessel. Ignition delay of diesel engine on various operation condition was calculated based on the new reduced chemical mechanism. The calculation results agreed well with experimental data.
In an HSDI Diesel engine, fuel can be injected into the combustion chamber earlier as a strategy to reduce NOx and soot emissions. However, in the case of early injection wall impingement may occur if the conventional spray angle and piston bowl shape are adapted. In this study, a 3-D CFD simulation was used to optimize the spray angle and the piston bowl shape to minimize the wall impingement and soot emissions. The wall impingement model was used to simulate the behavior of impinged droplets. In order to predict the performance and emissions of the engine, a flamelet combustion model with the kinetic chemical mechanism for NOx and soot was used. A reduction in soot emissions was achieved with the modification of the spray angle and piston bowl shape.