A computational study of DME-methanol fractions with controlling several factors on HCCI combustion

Abstract

Two-stage fuel and single stage fuel have different effects on ignition delay and other combustion characteristics. If we mix two fuels with variable fractions, combustion characteristics will be represented with dependence on the fraction. We first investigated the change of combustion characteristics and combustion ranges by dimethyl ether (DME)/methanol fraction, IVC temperature and IVC pressure. By increasing methanol fraction, Heat release rate (HRR) showed higher rate than the case containing less methanol after 1250 K. However, it didn’t mean that Accumulated heat release (AHR) was also higher than the cases which contained less methanol. AHR of D90/M10 was the first case which surpassed AHR of D100 at about 1808K, and D80/M20 surpassed D100 at about 2318K. The result was caused by change of reaction mechanism and the change was remarkably shown in the Thermal ignition preparation (TIP) range and the Thermal ignition (TI) range. Above all, strengthened H2O2 Loop reactions affected heat production to increase in TIP range, and also one of the loop reactions, CH2O + OH = HCO + H2O, quickly produced formyl radical with increase of net reaction rate by methanol. Those results naturally led to higher reaction rates of HCO-CO-CO2 oxidation with higher heat production. As a result, D50/M50 case showed the highest maximum Pressure rise rate (PRR). Furthermore, dispersion rate of PRR was increased by increasing methanol fraction in the range which was from back end of TIP to forepart of TI range. Finally, we focused the reaction paths of two fuels and the production and consumption rate of main radicals on the basis of combustion ranges such as LTO, Negative temperature coefficient (NTC), Thermal ignition preparation (TIP) and Thermal ignition (TI) to understand the results of this study.