Experimental study on the effects of injection timing and n-butanol energy ratio on combustion and emissions of n-butanol/diesel DFDI engine

Abstract

In this paper, a dual-fuel direct injection (DFDI) system was designed by utilizing two common-rail direct-injection systems in a modified single-cylinder engine. Diesel and n-butanol were directly injected to realize the stratifications of fuel-air mixtures and reactivity. The effects of the n-butanol energy ratio (BER) and fuel injection timing on engine combustion and emission characteristics were studied under low and medium load. The combustion phase was retarded, indicated thermal efficiency (ITE) decreased and COV of IMEP increased as increasing BER under each load. Under low load, the n-butanol injection timing was suggested near 125° CA BTDC to increase ITE, by modifying the stratification of the n-butanol at a favorable level. With an advance of diesel injection timing, the combustion phase was advanced at first and then retarded; ITE was also increased firstly and then decreased. Under medium load, the two-stage high temperature heat release event could be observed. Early n-butanol injection condition was preferred to achieve higher ITE and lower COV of IMEP. The early diesel injection operation was suggested under medium load for increased ITE, together with the decreased nitrogen oxide and soot emissions. In general, compared with pure diesel operation, stable and high-efficient combustion could be achieved in n-butanol/diesel DFDI mode, while the ITE could increase 2.8%; NOx and Soot emission decreased 82% and 79%.