Abstract
A thermal efficiency improvement effect by the independent control of engine effective compression ratio and expansion ratio was theoretically and experimentally confirmed in the previous paper. In this paper, the effect of further increase in the expansion ratio (geometric compression ratio, namely piston cavity volume reduction) was investigated by both numerical calculation and single cylinder heavy-duty diesel engine experiment. As a result, the potential of further thermal efficiency improvement was certainly confirmed while some issues were revealed i.e. each energy loss was increased so as not to be able to ignore it.
