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Abstract In-cylinder air flow structures are known to strongly impact on the performance and combustion of internal combustion engines (ICE). Therefore, the aim of this paper is to experimentally study an IC engine in-cylinder flow under steady-state conditions. Steady-state flow bench methods can be used to characterize the in-cylinder flow engine. The experiments were carried out on the small cylinder head with pressure difference across the inlet valves of 100 to 300 mmH 2 O. The experimental results are presented in terms of the measured air flow rate, flow coefficient and discharge coefficient. Moreover, the CFD used to illustrate the evolution of tumble motion in-cylinder engine. The results show that air volume flow rate and flow coefficient increased as the valve lift increases but the coefficient of discharge decrease if valve lift increase. The higher the pressure drop the higher the mass flow rate value. However, the higher the pressure drop the lower the value of flow coefficient and discharge coefficient. [ABSTRACT FROM AUTHOR]

Because air cooled small engines have very low compression ratio and fixed ignition timing, and work on slightly rich mixtures, their specific fuel consumption and emission values are very high. In this study, some modifications were made to improve performance and to reduce emissions in a small engine. The compression ratio of this engine was raised from 5:1 to 10:1, the ignition system was powered and the ignition timing was converted to be variable. The modified engine was operated with lean mixtures at high compression ratio. The test results showed that the power of the modified engine was higher than that of the standard engine by ~32%. At the same time, the specific fuel consumption and the HG emissions were reduced by ~36 and 31% respectively. According to these results, it can be said that there is the potential of performance improvement and emission reduction in the small engines without using any fuel injection system and exhaust control system which increase cost of engine. [ABSTRACT FROM AUTHOR]