Experimental and kinetic modeling studies on the interaction of DMM3-isooctane blends during the low-temperature oxidation

Abstract

Reactivity controlled compression ignition (RCCI) engines have been extensively investigated in the past decade due to its good performance in balancing the NOx-soot trade off relationship and controlling the heat release rate. However, studies on the interaction between the reactive and inert fuels are scarce, which is critical for regulating the RCCI combustion process. In this study, the interaction mechanism between polyoxymethylene dimethyl ethers (DMM3) and isooctane during the low-temperature oxidation was investigated through experiments and simulations. The low-temperature oxidation experiments were conducted in a jet-stirred reactor (JSR) at near atmospheric pressure with different blending ratios. A detailed DMM3-isooctane mechanism containing 2896 species and 9676 reactions was developed and fully validated with the experimental results. In addition, an impact factor fw was proposed to quantitatively analyze the influence degree of interaction between fuel and intermediate species. The results indicate that the low-temperature oxidation of isooctane is triggered and significantly enhanced in the blending fuels. The OH radicals generated by DMM3 are crucial to trigger the low-temperature reaction of isooctane and always play a dominant role in the whole isooctane oxidation process. In addition, isooctane reveals an intense inhibition on the formation of two key intermediate species of DMM3, i.e., methyl formate and methoxymethyl formate. This inhibitory effect ranges from the beginning of low-temperature oxidation of DMM3 to the end of the NTC process (580 K ∼ 750 K). When the temperature is higher than 800 K, the inhibitory effect of isooctane on methyl formate and methoxymethyl formate is significantly weakened and negligible. In addition, the blending of inactive isooctane will result in an oxygen-rich environment for DMM3 during the low-temperature oxidation, which will accelerate the formation of methyl formate and methoxymethyl formate. However, this promoting effect is limited, compared with inhibiting effect of isooctane.