Ignition of Lean CO/H₂/Air Mixtures at Elevated Pressures

Shock-tube ignition delay time experiments and chemical kinetics model calculations were performed for several fuel blends of carbon monoxide and hydrogen in air at elevated pressures. Due to the interest in coal-derived fuels, namely syngas, these data are important for characterizing the ignition and oxidation of possible fuel blends used in gas turbines and for the validation of chemical kinetics models. Three lean, CO/H₂ (80/20%, 90/10%, and 95/5% by volume) fuel blends in air were studied behind reflected shock waves at temperatures between 929 and 1304 K and pressures ranging from 1.7 to 15 atm. Ignition delay times were monitored using chemiluminescence emission from excited hydroxyl radicals. Results exhibit the second-explosion limit behavior from hydrogen oxidation kinetics at low temperatures and high pressures for all mixtures. In addition, comparisons of modeling results and experimental data show good agreement for the entire temperature range at high pressure and poor agreement with the data at low temperatures in the intermediate pressure regimes. Ignition and reaction sensitivity analyses indicate that the H + O₂ + M = HO₂ + M termination reaction is important at all conditions herein, and the early formation of HO₂ suppresses the growth of the ignition-enhancing radicals H and OH.