Experimental and kinetic studies of acetylene flames at elevated pressures

The kinetic effects of CO2 and H2O dilution on the laminar flame speed of acetylene at elevated pressures have been investigated experimentally using outwardly propagating spherical flames in a nearly constant pressure chamber from 1 to 20 atm. The flame speeds of C2H2/air mixtures at atmospheric pressure agree with recent measurements reasonably well. Detailed analysis on the combustion chemistry of acetylene reveals that C2H2 + O, HCCO + O2, HCO + O2, CH3 + HO2, H + C2H3, CO + OH, CH2(S) + C2H2, and HCO decomposition are among the most important reactions, which leads to a new kinetic model (HP Mech) that incorporates the recent understanding of elementary reactions. The effects of CO2 dilution on acetylene flame speeds are found to be small for both fuel rich and lean conditions due to the direct CO2 formation pathway (HCCO + O2) in acetylene oxidation. Water dilution effects are more pronounced, especially at lean conditions, because the radical pool composition is altered by shifting the equilibrium of H2O + O = OH + OH. Comparing to USC Mech II, HP Mech has much better performance compared to the current experimental measurements as well as the shock tube and flow reactor data.