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A new empirical formula for instantaneous heat transfer coefficients was determined. The determination of this formula is in necessary for prediction of the instantaneous value of heat transfer coefficients to analyze in more detail the time variation of heat transfer rate from the gas to the wall in the combustion chamber of a spark ignition engine. The following formula was determined. Using this empirical formula the instantaneous heat transfer coefficients of gas in the combustion chamber of spark ignition engine was predicted and compared with experimental values.

The design and development of a turbocharged engine requires an understanding of the characteristics of engine performance and thermal flow. In this study a naturally aspirated gasoline engine was equipped with a turbocharger. A thin-film temperature probe was manufactured and was installed into the combustion chamber wall to measure the unsteady temperature. The unsteady heat flux at the combustion chamber wall was evaluated by a one dimensional unsteady conduction equation with the wall temperature and temperature gradient.

Turbocharged lean combustion was realized by using a multi-spark ignition device. The turbocharged lean operation in air-fuel ratio of 21:1 got the same torque level as the stoichiometric air-fuel ratio operation in naturally aspirated engine. For the turbocharged operation, NO and CO emissions remarkably reduced about 80 per cent and 85 per cent respectively and unburned HC increased about 30 per cent in condition of air-fuel ratio of 21:1 compared with stoichiometric air-fuel ratio. When compression ratio was increased, brake power and brake thermal efficiency increased and NO, CO and HC in exhaust emissions also increased. Combustion stability was estimated by using the coefficient of variation in indicated mean effective pressure. COVimep decreased when compression ratio was increased, but that value exceeded 10 per cent in low speed range. Accordingly, one of the important problems to be resolved in lean combustion is combustion stability in low speed range.

Combustion in a spark-ignition engine is affected by the complicated gas movement. It is difficult to analyze such combustion process. However, the combustion modeling is very useful for the analysis of the combustion process. For this purpose, we made use of the entrainment model and expressed the turbulent flame velocity as a function of laminar flame velocity, simplified combustion-chamber shape and inlet flow velocity. As the results of this paper, we found that the predicted rate of mass burned by this method is similar to the value obtained by the analysis of the indicator diagram. The turbulent flame velocity was found to be affected greatly by the engine speed and the combustion chamber shape. The flame factor which is the characteristic constant of the experimental engine, can be determined by the variables such as laminar flame velocity, engine speed and combustion chamber shape. The relation of flame factor with each of these variables is closely examined in this paper.