A comparative study on operating range and combustion characteristics of methanol/diesel dual direct injection engine with different methanol injection timings

Abstract

Improved combustion and reduction in emissions levels could be achieved with optimization of in-cylinder fuel–air mixing. According to the engine operating condition, the spatial and temporal features of in-cylinder mixture can be flexibly and accurately adjusted by methanol/diesel dual direct injection in real time. Present research investigated the effect of dual direct injection strategy on the operating range, combustion and emissions characteristics of a methanol/diesel dual direct injection engine. The results showed that the limits of the engine operating range could be obtained by observing the unstable and roar combustion in the cylinder when the methanol was injected directly during the intake stroke. The onset of roar combustion provided the upper bound of operating range at the methanol injection timing (SOIM) of − 60 °CA aTDC. High indicated thermal efficiency (ITE) could be achieved accompanied by widening the operating range of the engine. Systematic analysis results of combustion characteristics indicated that the increments of engine load and methanol energy substation ratio (ESR) were conducive to improving the combustion stability of the engine. Because of the reduced diffusion-controlled combustion, the methanol/diesel dual fuel direct injection strategy could realize a relatively low NOx emissions, which were insensitive to the SOIM at low ESR conditions. With the increase of ESR, injecting methanol close to TDC resulted in lower CO and HC emissions, especially at higher engine load conditions. This study confirms that the implementation of dual direct injection strategy has the potential to extend the operating range of a methanol/diesel engine, accompanied with high fuel economy and low emissions.