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This study presents engine test results of HMC's piston-ported 2-stroke gasoline engine. This single cylinder engine of 400cc displacement has featured in direct injection(DI) of fuel and external blower scavenging of air. Two different concepts of DI system were adopted, one is high pressure fuel injection(HPFI) system for solid fuel only and the other is low pressure air-assisted fuel injection(AAFI) system. Two kinds of engines with different scavenging intake port shapes and areas were tested to find the effect of scavenging port type on engine performance. Also tested were trends of BSFC, BSHC and BSCO versus fuel injection timing and engine speed with HPFI and AAFI, respectively. Power and boost pressure at full load and BSFC and BSHC at part load were tested.

An experiment has been carried out to investigate the combustion process in an operating S.I. engine (MPI and Multi- valve), using in-cylinder high speed gas sampling techniques. Measurements have been made of local air fuel ratios and time-resolved concentrations of combustion gases such as CO, CO2, THC, NOx, and O2, particularly focused on spark plug location. The effects of fuel injection timing, swirl generating air motion, sampling location, spark timing, speed and load have been considered. With the end of fuel injection at 120° ATDC on the intake stroke, A/F ratio at spark plug location has the leanest value for standard inlet port, while it has the richest value for swirl generating inlet port. The initial NOx concentration in the unburned gas region, diluted by the residual gases, has been substantially reduced between 5° BTDC and 15° ATDC crank angle prior to combustion.