A four-step reduced mechanism for syngas combustion

A four-step reduced chemical-kinetic mechanism for syngas combustion is proposed for use under conditions of interest for gas-turbine operation. The mechanism builds upon our recently published threestep mechanism for H2-air combustion (Boivin et al., Proc. Comb. Inst. 33, 2010), which was derived from a 12-step skeletal mechanism by assuming O, OH, and H2O2 to be in chemical-kinetic steady state and includes a correction to account for the failure of the O and OH steady states during autoignition. The analysis begins by appropriately extending the number of elementary steps in the skeletal description to enable computation of the CO chemistry for mixtures with appreciable H2 content, giving a total of 16 elementary steps. It is seen that the formyl radical HCO, which appears as the only additional relevant intermediate in the extended chemical description, follows accurately a steady-state approximation, which can be used along with the steady-state approximations for O, OH, and H2O2 to derive the reduced description, involving the three global steps of our previous H2-air mechanism, 3H2+O2 2H2O+2H, 2H+M H2+M, and H2+O2 HO2+H, along with the additional step CO+ H2O CO2+H2. Expressions are given for the rates of the four global reactions in terms of those of the elementary steps of the skeletal mechanism, with concentrations of the different steady-state species also given in explicit form. Comparisons of results of computations of laminar burning velocities and induction times with published experimental data for H2/CO/O2 mixtures with different diluents at atmospheric and elevated pressures and for varying equivalence ratios and initial temperatures indicate that the reduced description can be applied with reasonable accuracy in numerical studies of gas-turbine syngas combustion.This work was supported by the UE Marie Curie ITN MYPLANET, by the Comunidad de Madrid through project # S2009/ENE-1597, and by the Spanish MCINN through projects # ENE2008-06515 and CSD2010-00011.European Community's Seventh Framework ProgramPublicad