REACTION MODELING OF AUTO-IGNITION AND EXHAUST EMISSION IN COMPRESSION-IGNITION COMBUSTION

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Three different types of reaction models have been developed for the compression-ignition process in Diesel engines to be coupled with exhaust emission analyzes.The first model is to describe the high temperature oxidation process from fuel to CO and H_2 with one-step global mechanism of Edelman followed by a detailed kinetics of the oxidation of CO and H_2. In addition to these models, a model for NO formation including prompt NO and thermal NO were taken into account. These reactions were integrated in the stochastic model which expressed the random collisions in turbulent mixing between gas blobs having different temperatures and species concentrations. The computed results compared well with measurements of NO concentration in Diesel exhaust.The second model expresses not only the heat release but also the cracking process which is essential to modeling the soot formation. The model consists of following multi-step global reactions based on the Rice-Herzfeld mechanism and the C_2 hydrocarbon chemistry.C_mH_n*aC_2H_4+bC_4H_9 : n-C_4H_9*C_2H_4+C_2H_5 ; i-C_4H_9*C_3H_6+CH_3The rate constant for the above global reaction was obtaned by comparing with the ignition delay measured in a rapid compression machine. The computed fractions of CH_4, C_2H_4, C_2H_6 and C_3H_6 showed good agreement with measurements.The third model describes the low temperature oxidation mechanism which is needed to analyze a premixed compression-ignition proces. Based on Keck's model, the model has been established by modifying rate constants, activation energies and the mechanism of the termination reaction to fit existing experimental results.The models developed in this study will lead to a more realistic model to combine the high and low temperature mechanisms for the auto-ignition process in the premixed compression-ignition engines being developed for one of the potential future internal combustion engines.