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An experimental study on the tumble flow and turbulence characteristics in a small four-valve engine has been performed to provide better understanding of the formation and decay mechanisms of tumble and its effects on turbulence. The detailed comparison of the decay mechanisms of tumble during compression by means of two newly defined non-dimensional parameters, in addition to the tumble moment, has been effectively performed. The turbulence was analyzed in terms of turbulence intensity, integral time scales, and integral length scale. With tumble flow, the turbulence intensity at the end of compression was found to increase twice and the turbulence field became more homogeneous. The turbulence integral time scale during the compression was found to be inversely proportional to the engine speed, regardless of existence of tumble flow. However, the integral length scale is strongly affected and increased by tumble flow.

Optimization study is performed for the scavenging process as the first step for the development of a poppet-valve type automotive two-stroke diesel engine. The scavenging flow pattern is varied by the RSSV (rotatable shrouded scavenging valve) system, which was designed for application of a shroud valve to an actual engine. The scavenging flow is analyzed by flow visualization and numerical calculations under a steady condition. Water is used as the working fluid, instead of air for effective visualization of the flow pattern in the flow visualization study. More details in the scavenging characteristics are observed by a dye experiment, in which the dye path indicates the flow streamline in the cylinder. In the numerical study, three-dimensional flows are calculated by a modified version of KIVA-2 code, with a special technique to consider the valve and shroud shapes.

A new rotary type carburetor was developed for a gasoline engine. It has a rotor which feeds fuel into an engine proportionally to the inlet air flowrate. Comparing with a conventional venturi type carburetor it was simple in design with less parts. The rotary type carburetor was tested on an engine dynamometer for the various engine operating conditions. During acceleration and deceleration, the rotary type carburetor could not supply the fuel adequately, resulted in unstable engine operation. Under steady running conditions the rotary type carburetor was superior to venturi type in power and fuel economy. It was concluded from the experimental study that the rotary type carburetor is more suitable for the steady running gasoline engines especially at high speeds.

A computer model is developed to predict engine performance and exhaust emissions in a spark-ignition engine. In the model, combustion phenomenon is analyzed by the turbulent combustion model which considers the effect of the turbulence and the combustion chamber on combustion. The gas exchange process is calculated by one dimensional isentropic flow through a nozzle. During combustion, 13 products are obtained by chemical equilibrium, and nitric oxide (NO) formation is calculated by the extended Zeldovich mechanism. The results of the computer model are compared with the experimental results. The calculated values for pressure and NO emission show good agreement “with the experimental data. The effects of the engine speed, spark timing, air fuel ratio, and EGR are studied by the model.