Two-step chemical-kinetic descriptions for hydrocarbon–oxygen-diluent ignition and detonation applications

Abstract

Two-step chemical-kinetic mechanisms for acetylene, ethylene, propane, and JP-10 detonations in oxygen-diluent mixtures are described for use in detonation studies. Conditions addressed cover post-shock temperatures between 1300 and 2500 K, pressures between 1 and 100 bar, and equivalence ratios from 0.5 to 2.0. These mechanisms were developed through reduction from a detailed mechanism consisting of 193 reactions among 41 species that has been tested extensively against shock tube ignition times, counter flow flame-structure measurements, and flame-speed data from literature. Ignition times and temperature histories from the simplified descriptions are in good agreement with those from the detailed mechanism. For all of these fuels, the two-step mechanism consists of a fuel-consumption step that produces radicals, CO, and H 2O and releases most of the heat, followed by a CO-oxidation, radical-recombination step, which releases the remainder of the heat thus approaching equilibrium. For acetylene and ethylene, the first step proceeds at a rate, which is the sum of the rates of an initiation step and the H + O 2 branching step. For propane and JP-10, due to the fundamentally different chemical-kinetic processes involved, this step has been assigned a rate that is proportional to a characteristic fuel-consumption rate. The second step proceeds at the rate of the elementary H + OH recombination reaction. More complex descriptions involving skeletal mechanisms are available for acetylene, ethylene, and propane. Encouraging results have been obtained through applications of these simplified mechanisms in detonation studies.