Investigation into the operating range of a dual-direct injection engine fueled with methanol and diesel

Dual-fuel combustion mode suffers from poor fuel economy at low load and roar combustion at high load. Dual-fuel direct injection is one of the most promising strategies to control mixing process in a dual-fuel engine. In this paper, dual-fuel direct injection mode was developed by two decoupled injection systems. The experiments were conducted to investigate the operating range with regard to methanol energy substitution ratio (ESR) and engine load on combustion and emissions characteristics of dual-fuel direct injection mode. Results show that as the methanol injection quantity increases, the maximum ESR can reach up to 65.1%, while it is restricted by roar combustion at high engine load. The methanol/diesel dual-direct injection engine could achieve a globally optimized goal at 52.4% ESR with the highest indicated thermal efficiency (ITE) being 43.4%. At low engine load, the inhibition effect of the methanol addition on the combustion phasing and stability becomes more superior. At medium to high loads, the increasing ESR can increase the combustion rate and combustion stability together with decreased NOx emissions. However, the HC and CO emissions of dual direct injection mode are inferior to that of neat diesel mode.