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In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate (dP/dθ) were investigated through theoretical and experimental methods. The Blow-Down Super Charge (BDSC) and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. And also, to control the distribution of fuel concentration, direct fuel injection system was used. As a first step, the effect of spatial temperature distribution on maximum pressure rise rate (dP/dθmax) was investigated. The influence of the EGR guide parts on the temperature distribution was investigated using 3-D numerical simulation. Simulation results showed that the temperature difference between high temperature zone and low temperature zone increased by using EGR guide parts together with the BDSC system.

Motorcycles have been classified by engine displacement from commercial and legal demands. If this restriction on displacement were removed, what could be done to improve fuel economy? “Down sizing” would be an obvious idea. However this paper proposes a quite inverse concept, i.e. a large displacement lower speed engine. Mechanical friction in four-stroke engines generally decreases in proportion to the square of engine speed. Thus mechanical efficiency should be better at lower operation speeds. According to this concept, developing a 200cm3 experimental engine was successful in improving fuel economy by 79% in the ECE40 mode and by 97% at 60km/h cruise condition, compared to the 100cm3 original engine.