(1-07) Prediction of Ignition Processes in Fuel Sprays Including Turbulent Mixing and Reduced Chemical Reaction Models((DE-3)Diesel Engine Combustion 3-Modeling)

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Aiming at higher thermal efficiency, various types of spray/jet combustion have been developed for internal combustion engines such as diesel engines, gasoline direct-injection engines, gas-fueled direct-injection engines and premixed compression ignition engines. In the combustion techniques employed in these engines, there is much difference not only in fuel composition, charge air pressure and temperature but also in heterogeneity of fuel-air mixture, i. e., the extent of fuel-air mixing. The difference decides the characteristics of ignition and combustion processes in each engine. Therefore, the demand for better understanding of effects of fuel-air mixing on the ignition process has grown. From this point of view, in this study, the modeling of spray ignition processes was carried out with the emphasis on fuel-air mixing process. In the developed model, a stochastic mixing model and a reduced chemical reaction model are combined to represent the simultaneous progress of fuel-air mixing and chemical reaction. By using this model, effects of mixture heterogeneity on spray ignition processes were investigated. First, trends and effects of heterogeneity in temperature and equivalence ratio of mixture were investigated. As shown in Fig. A-1, ignition delays of heterogeneous mixture (spray ignition) have similar temperature dependence to those of homogeneous mixture at low temperatures, while at high temperatures the heterogeneous delays scarcely reflect the ignition characteristics in the homogeneous case. One of the reasons is the difference of mixture heterogeneity with temperature as shown in Fig. A-2. It is suggested that the combined effect of this heterogeneity and existence of the most ignitable mixture at each temperature of surrounding air is responsible for the phenomena. Investigations were also carried out on effects of turbulence scale and of air entrain rate on temperature dependency of ignition delay. The effects of heat absorption rate and distribution of equivalence ratio explain the phenomena caused by the change of these characteristics. Finally, the effects of nozzle orifice size and injection velocity were investigated as an example of simultaneous change of mixing rate and flow rate of entrained air.
一般社団法人日本機械学会の論文
2001-07-01

(1-07) Prediction of Ignition Processes in Fuel Sprays Including Turbulent Mixing and Reduced Chemical Reaction Models((DE-3)Diesel Engine Combustion 3-Modeling)

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