Effects of PODE substitution rate and fuel injection timing on combustion, emission characteristic and energy balance in PODE-gasoline dual direct-injection engine

Dual direct injection (DDI) mode allows two kinds of different reactivity fuels to be flexibly injected into the cylinders and offers lower pressure rise rate (PRR), CO and HC emissions than Reactivity Controlled Compression Ignition (RCCI) mode. Thus, a single-cylinder engine was modified to adopt two direct-injection systems to inject PODE and gasoline respectively in this paper. Due to high oxygen content and high cetane number, PODE was selected as a high reactivity fuel to replace diesel in the experiments. The effects of different PODE substitution rates(PSR), PODE injection timing(injP) and gasoline injection timing(injG) on the combustion, emission characteristics and energy balance were studied. The results concluded the using PODE-gasoline mode could increase the indicated thermal efficiency(ITE) and reduce exhaust losses compared to the diesel-gasoline mode. As PSR increased, it led to the increased ITE and effective power, decreased CO, HC emissions. Compared to the PODE late injection mode, the effective power and ITE were higher, and CO, HC emissions were lower in the PODE early injection mode. The coefficient of variation of IMEP(COVIMEP) for the DDI combustion was also in an acceptable range. Furthermore, an early injG could lead to higher ITE, lower COVIMEP, CO and HC.