Inhibition of autoignition and combustion rate for n-heptane homogeneous charge compression ignition combustion by methanol additive

Abstract

This paper investigated the effects of methanol additive on autoignition and combustion rate of homogeneous charge compression ignition (HCCI) combustion using n-heptane. n-Heptane and 10–40 per cent (v/v) methanol/n-heptane blend fuels were injected into the intake port. The combustion characteristics and emissions of HCCI combustion for different methanol/n-heptane blend fuels at 1800r/min were recorded and analysed. The results show that the ignition timing of low- and high-temperature reaction is delayed and the maximum heat release during the low-temperature stage decreases with the increase in methanol addition in n-heptane. Sequentially, both the maximum and minimum accepted equivalence ratio increase, but the maximum engine load could not be further expanded beyond 40 per cent and above methanol/n-heptane fuels. For 20 and 30 per cent methanol/ n-heptane blend fuels, the combustion phasing of the high-temperature reaction occurs between -5-5° CA ATDC (crank angle after top dead centre) and the combustion events accomplished during the expanding stroke. With regard to the emissions, 10 and 20 per cent methanol addition shows little effect on CO and HC emissions, but substantially increases for 30 and 40 per cent methanol/n-heptane blend fuels. NOx emissions are greatly lowered for all fuels.