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Three-dimensional combustion simulation tools together with the Universal Coherent Flamelet Model (UCFM), a flame propagation model, have been applied to SI lean-burn combustion to study the influence of the equivalence ratio on the amount of unburned hydrocarbons (HCs). Unburned HCs from piston-cylinder crevices were taken into the consideration by using a calculation grid incorporating the actual crevice volume and shape and by applying an autoignition model to post-flame phenomena. The calculation results show the general tendencies for the total amount of unburned HCs and their distribution in the combustion chamber.

A transient knock prediction technique has been developed by coupling a zero-dimensional knocking simulation with chemical kinetics and a one-dimensional gas exchange engine model to study the occurrence of transient knock in SI engines. A mixed chemical reaction mechanism of the primary reference fuels was implemented in the two-zone combustion chamber model as the auto-ignition model of the end-gas. An empirical correlation between end-gas auto-ignition and knock intensity obtained through intensive analysis of experimental data has been applied to the knocking simulation with the aim of obtaining better prediction accuracy. The results of calculations made under various engine operating parameters show good agreement with experimental data for trace knock sensitivity to spark advance.

Combustion in engines involves very complicated phenomena (including flame propagation and knocking), which are strongly affected by engine speed, load and turbulence intensity in the combustion chamber. The aim of this study was to develop a flame propagation model and a knocking prediction technique applicable to various engine operating conditions, including engine speed and in-cylinder turbulence intensity. A flame propagation model (UCFM) has been developed that improved the Coherent Flamelet Model by considering flame growth both in terms of the turbulent flame kernel and laminar flame kernel. A knocking prediction model was developed by implementing the Livengood-Wu integral as the autoignition model. The combined model allows evaluation of both where and when autoignition occurs in a real shape combustion chamber. A comparison of the measured and calculated time for the occurrence of knocking shows good agreement for various operating conditions.