Study on the decision process of basic specification in development of general purpose engine

Social interest in global environmental issues has remained in the forefront during recent years, and as a result, internal combustion engines are expected to have further improved fuel efficiency and reduced exhaust emissions. General purpose engines are demanded for reduced cost in addition to various types of displacement developments. If optimum specifications are examined for each engine displacement and incorporated in the parts shapes, the number of dedicated parts for each engine displacement would increase, which is not desirable from a development/production cost-wise standpoint. It is considered important during the development of engines to efficiently and economically cope with market needs including improved specific power and fuel consumption. Therefore, it was considered necessary to improve combustion performance by enhanced in-cylinder flow and to commonize parts. Then, this study was designed to establish an approach for decision of engine specifications with the perspective of multiple displacement development after satisfying the target performance by combustion improvement. The long stroke and valve angle were adjusted so as to examine specifications that enable enhanced in-cylinder flow with multiple displacements. By confirming that combustion characteristic and fuel efficiency characteristic are correlated to turbulence intensity in cylinder as well as by focusing on Turbulent Kinetic Energy and stroke/bore ratio, engine specifications satisfying the target performance with multiple engine displacements was decided. By making stroke common, it has become possible configure engines of various displacements that satisfy the target performance while achieving reduction of the total number of parts and cost reduction. As a result of verification of the decided specifications by using prototype engines, it was found that the improvement of specific power and fuel efficiency was achieved in comparison to the base engine.