Effects of methanol energy substitution ratio and diesel injection timing on a methanol/diesel dual-fuel direct injection engine

Abstract

Dual-direct injection technology is a very promising method to improve the mixture organization and combustion process of dual-fuel engines. In this paper, the performance of a modified dual-fuel engine fueled with methanol and diesel has been explored experimentally at various methanol energy substitution ratios (ESR_Ms) and diesel injection timings (SOI_Ds). Independent injection of methanol and diesel is realized in real time and accurately through a dual-direct injection system with by two different in-cylinder injectors based on engine operating status. The results show that the dual-direct injection technology has great potential to expand the operating range of the engine, with the improvement of indicated thermal efficiency (ITE) and the reduction of pollutant emissions. It is noted that ESR_M and SOI_D are both very significant factors to influence the combustion phasing and exothermic process. As the SOI_D advances, the combustion process is enhanced and the HC, CO and soot emissions are limited, while the NO_x emissions are sacrificed to some extent. By optimizing of ESR_M, synchronous optimization of ITE and NO_x has been realized. As the ESR_M increases, the ITE increases first, achieving a maximum value of 41.5% at 50% ESR_M, and then decreases quickly, which is opposite to the HC and CO emissions. However, NO_x and soot emissions are consistently reduced as the ESR_M increases. Compared with SOI_D, the ITE is highly sensitive to the ESR_M. Moreover, the combustion stability can be enhanced effectively through the collaborative optimization of SOI_D and ESR_M.