Abstract
This study is to clarify the effect of the optimum compression and expansion ratio control on the thermal efficiency by variable valve timings with a single-cylinder heavy duty diesel engine equipped with external supercharging system. Test was done in various combinations of effective compression and expansion ratio. In conclusion, it is confirmed that improvement in the gross indicated thermal efficiency by increasing effective expansion ratio at fixed and relatively lower effective compression ratio than expansion ratio. Brake thermal efficiency was further improved with the cavity having higher geometrical compression ratio than the baseline having 18.0 of compression ratio.
