Effect of Compression Ratio on Improving Thermal Efficiency and Output Power in Hydrogen HCCI Engine Supported by DME Supplement

Abstract

Improvement in output power and indicated thermal efficiency were achieved by lowering compression ratio from 13:1 to 11:1 hydrogen HCCI engine supported by DME supplement. Improved output power was realized by the truth that mitigated HCCI combustion derived by lowered compression ratio enabled stable HCCI combustion without showing any knocking inλof close to 2, which is much richer than 2.7 that is limited by knocking in compression ratio of 13:1. Improved indicated thermal efficiency was achieved by the ratarded onset of heat release around 1 to 3 deg. CA compared with compression ration of 13:1 and resulted in reduced heat loss to the cylinder wall. On the contrary, since misfiring limit was also shifted to the richer mixture region, stable operating range was not always expanded.