Low to intermediate temperature oxidation studies of dimethoxymethane/n-heptane blends in a jet-stirred reactor

Kinetic research concerning fuel blends of ethers or dithers and larger alkanes at low temperatures is extremely scarce. In this work, a study of the oxidation of dimethoxymethane (DMM)/n-heptane fuel blends (neat n-heptane, 25/75, 50/50, neat DMM) was performed using an atmospheric pressure jet-stirred reactor over the temperature range of 500-1100 K, at a residence time of 2.0 s, at three equivalence ratios (0.5, 1.0, and 2.0), and at a constant fuel inlet mole fraction of 0.005 (with high dilution in argon). The reliability of the newly built JSR setup was validated against literature data. A chemical kinetic model capable of describing the low temperature chemistry of the fuel blends was constructed. The effect of using AramcoMech 1.3 and AramcoMech 2.0, respectively, as the base-mechanism has been tested and some important reactions such as H +O-2 (+M) double left right arrow HO2 (+M), have been found to be responsible for their different performances. Not unexpectedly, the reactivity of DMM is remarkably enhanced in the fuel blends and correspondingly, that of n-heptane is inhibited. To quantify the degree to which the reactivity of n-heptane is inhibited, an inhibiting coefficient was introduced. It is interesting that the correlation between the inhibiting intensity and equivalence ratio is non-monotonic. Rate of production analysis was conducted to investigate the chemical interaction effect on their respective decomposition pathways at lower temperatures. Kinetic analysis combined with the experimental observations indicate that the rate coefficients for H-abstraction reactions by OH from DMM were overestimated. Possible modifications to the reaction rate of this reaction type were suggested, leading to a better prediction. Three intermediate representatives were discussed in detail to elucidate the chemical interactions between the two fuel components. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.