A comprehensive experimental and kinetic modeling study of methyl tert-butyl ether combustion

A comprehensive understanding of the combustion chemistry of methyl tert-butyl ether (MTBE) is of key importance in its application as an additive in gasoline fuels. Ignition delay times (IDTs) of MTBE/air mixtures have been measured in both a high-pressure shock tube (HPST) and in a rapid compression machine (RCM) at equivalence ratios of 0.5, 1.0, and 2.0 in air, at pressures of 10 and 30 bar over the temperature range 600 - 1350 K. Species profiles for MTBE oxidation were obtained in a jet-stirred reactor (JSR) at 1 bar, at equivalence ratios of 0.5, 1.0, and 2.0 in the temperature range 700 - 1100 K. A detailed reaction mechanism, comprising 813 species and 4319 reactions, has been developed and predicts well all of the experimental data obtained in this work and also texisitng literature data. Pressure- and temperature-dependent rate constants for the MTBE unimolecular elimination reaction producing isobutene and methanol were calculated using high-level ab-initio calculations. A sensitivity analysis reveals that this elimination reaction is important, and significantly inhibits fuel reactivity at temperatures above 1300 K. At intermediate temperatures (850 - 1300 K), the reaction MTBE + (O)over dotH = T(C)over dot(4)H(8)OCH(3) + H2O plays a crucial role in promoting the reactivity of MTBE oxidation, whereas the reaction MTBE + (O)over dotH = TC4H9O (C)over dotH(2) + H2O is the most inhibiting reaction. At low temperatures (600 - 850 K), the isomerization reaction of TC4OC(O)over dot(2)-1 reversible arrow T(C)over dot(4)OCO(2)H-2 significantly promotes the reactivity. Conversely, the reaction 2TC(4)OC(O)over dot(2)-1 <-> 2TC(4)OC(O)over dot-1 + O-2 inhibits reactivity the most. The NTC behavior in MTBE oxidation can be explained by the competition between the reactions involving the formation and consumption of cyclic ethers from T(C)over dot(4)H(8)OCH(3) radicals and the reactions associated with the formation and consumption of carbonyl hydroperoxide species.