Laminar Flame Speeds and Strain Sensitivities of Mixtures of $H2∕O2∕N2$ at Elevated Preheat Temperatures

Laminar flame speeds and strain sensitivities of mixtures of $H2$ and air or air highly diluted with $N2$ (⁠$O2:N2$ 1:9) have been measured for a range of equivalence ratios at high preheat conditions $(∼700K)$ using a nozzle generated, 1D, laminar, wall stagnation flame. The measurements are compared with numerical predictions based on three detailed kinetic models (GRIMECH 3.0, a $H2∕CO$ mechanism from Davis et al. (2004, “An Optimized Kinetic Model of H2∕CO Combustion,” Proc. Combust. Inst., 30, pp. 1283–1292) and a $H2$ mechanism from Li et al. (2004, “An Updated Comprehensive Kinetic Model of Hydrogen Combustion,” Int. J. Chem. Kinet., 36, pp. 566–575)). Sensitivity of the measurements to uncertainties in boundary conditions, e.g., wall temperature and nozzle velocity profile (plug or potential), is investigated through detailed numerical simulations and shown to be small. The flame speeds and strain sensitivities predicted by the models for preheated reactants are in reasonable agreement with the measurements for mixtures of $H2$ and standard air at very lean conditions. For $H2$ and $N2$ diluted air, however, all three mechanisms significantly overpredict the measurements, and the overprediction increases for leaner mixtures. In contrast, the models underpredict flame speeds for room temperature mixtures of $H2$ with both standard and $N2$ diluted air, based on comparisons with measurements in literature. Thus, we find that the temperature dependence of the hydrogen flame speed as predicted by all the models is greater than the actual temperature dependence (for both standard and diluted air). Finally, the models are found to underpredict the measured strain sensitivity of the flame speed for $H2$ burning in $N2$ diluted air, especially away from stoichiometric conditions.