Technologies integration to achieve brake thermal efficiency beyond 55% for HD diesel engines

Abstract

This study focuses on the technologies integration to aim about 60% indicated thermal efficiency (ITE) with a single-cylinder HD diesel engine, roughly equivalent to 55% brake thermal efficiency (BTE) with multiple-cylinder engines. A new thermodynamic cycle concept and a new heat insulation structure were discussed as the key integrated technologies. Otto cycle is the best thermodynamic cycle for ideal thermal efficiency. However, significant increase in heat release rate around top dead center results in higher cooling loss and sometimes in deterioration of late combustion under a higher compression ratio without any improvement in ITE. The newly proposed cycle is the hybrid of isobaric cycle and following steep pressure increase up to peak firing pressure (PFP) constraint from the timing when in-cylinder volume change rate becomes significant, which suppresses the average gas temperature. For further cooling loss reduction, the new in-cylinder wall insulating concept was investigated. The in-cylinder insulating effect was much significant by applying not only on the piston crown but also on the cooling side of piston. Although the test engine hasn’t been optimized yet, ITE was almost reached at about 60% by means of the multiple-injector concept with compression ratio of 23.5:1.