Evaluation of Chemiluminescence as a Combustion Diagnostic Under Varying Operating Conditions

Modeling of OH*, CH * and CO2 * chemiluminescence, using recently validated reaction mechanisms, is used to examine chemiluminescence sensing of heat release and equivalence ratio in lean, premixed methane and syngas (H2/CO) flames. The effect of pressure, reactant preheat, aerodynamic strain, fuel-air ratio and product recirculation on spatially integrated chemiluminescence signals are considered. In the syngas mixture studied (equal molar amounts of H2 and CO), heat release rate measurements with either OH * or CO2* chemiluminescence are predicted to exhibit significant sensitivity to equivalence ratio (), pressure, reactant temperature and (to a lesser extent) aerodynamic strain. At high pressures, the chemiluminescence is practically independent of strain rate. Mixing of hot products and reactants before burning (e.g., EGR) also has little impact. OH* chemiluminescence is found to have some advantages for heat release sensing in turbulent premixed flames at near stoichiometric conditions. It has a lower strain dependence and is less sensitive to variations than CO2 * for near stoichiometric mixtures. For leaner conditions, heat release measurements employing CO2 * may be advantageous, due to its lower dependence on , pressure and preheat temperature. The ratio of CO2 * to OH*