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Recently, studies and developments have been underway in many countries to introduce a new type of car (hereinafter referred to as “Commuter car”), characterized by ultra smallness, energy saving and low pollution, for short-range purposes, for example commutation, in urban areas (1).In our previous study, the characteristics of electric motors were noticed, and the series hybrid system was focused to power commuter cars.Therefore, a simulated commuter car based on a small electric vehicle (EV) was set on a chassis dynamometer to test the basic items (2) . From these results, a new simulated series hybrid type commuter car that uses a high-power AC motor and a high-efficiency power generator was set on the bench.By acceleration/deceleration bench tests, selection of the reduction gear ratio and optimization of power supply from the generator were investigated in order to achieve both the performance necessary and sufficient for the city driving and power management.

A natural gas direct injection test engine equipped with a newly developed natural gas injector was built. High total hydrocarbon (THC) emission at part-load and high NOx emission at high-load remain as problems for direct injection natural gas engines. THC reduction and combustion improvement by throttling and NOx reduction by EGR were investigated. The following results were obtained: (1) the combustion at light and medium load conditions is improved by throttling. It is possible to improve the thermal efficiency at light-load in spite of the pumping loss by throttling. THC emissions are greatly decreased in this condition; (2) a large NOx reduction can be obtained without combustion deterioration by appropriate EGR at high-load conditions; and (3) it is possible to decrease both THC and NOx emissions by both throttling and EGR at part-load conditions.