圧縮比および膨張比がディーゼル機関の性能・排気特性に及ぼす影響

Abstract

In order to investigate the possibility of thermal efficiency improvement by the higher expansion ratio in a diesel engine, an experiment was conducted by combining a compression ratio of 20.3 and the Miller cycle with the late intake valve closing (IVC), in addition to the standard IVC with a compression ratio of 18.3, using a single-cylinder diesel engine with a cylinder bore of 85 mm. The results show that when using a shallow piston cavity to increase the geometric compression (expansion) ratio, the fuel sprays impinged onto the bottom of the cavity and increased the smoke emission and the cooling loss, and the effect of increasing the expansion ratio cannot be effectively utilized. Therefore, as a result of investigating the influence the piston cavity shape, it was possible to significantly reduce the smoke emission by using a little bit narrow and deep combustion chamber.