An experimental and modeling study on the low temperature oxidation of surrogate for JP-8 part II: Comparison between neat 1,3,5-trimethylbenzene and its mixture with n-decane

The low temperature oxidation of neat 1,3,5-trimethylbenzene (T135MB) and n-decane/T135MB mixture as a surrogate for JP-8 has been investigated in a jet-stirred reactor over the temperature range of 500-1100 K at atmospheric pressure under fuel-rich condition with residence time from 2.33 to 1.06 s. Mole fraction profiles of 29 intermediates including light hydrocarbons, oxygenated and aromatic compounds were identified by gas chromatographic techniques. In general, the concentrations of intermediates tend to increase progressively with temperature from 925 K in neat T135MB oxidation, while these species exhibit bimodal distributions from 550 K in the oxidation of n-decane/T135MB mixture (surrogate). By considering the calculated rate constants of T135MB and analogous coupling reactions between T135MB and n-decane, a detailed kinetic mechanism involving 910 species and 5329 reactions was established with a reasonable agreement with the experimental results. The low temperature chemistry of T135MB and surrogate was analyzed including the NTC behavior below 800 K. The oxidation process of T135MB is occurring mainly by H-abstraction with OH radical and subsequent reactions. The difference is that in the NTC region H-abstraction by OH radicals is the major consumption pathway for T135MB in the surrogate. But for neat T135MB, the dominant channels change to the H-abstractions by H-atoms, OH and CH3 radicals. Addition of n-decane can promote the oxidation of T135MB by providing OH radicals in the low temperature oxidation of surrogate fuel. Moreover, the model was also validated against the experimental data on n-decane and JP-8 combustion, including species profiles in low temperature jet-stirred reactor oxidation and high temperature flow reactor pyrolysis as well as ignition delay times. These extended results yielded overall satisfactory agreement, and will benefit for further application of practical JP-8 fuels, particularly for their combustion properties at wide temperature range.