Systematically derived reduced kinetics for hydrogen/ammonia gas-turbine combustion

Starting with a detailed-chemistry description involving 20 elementary steps for hydrogen oxidation and 40 elementary steps for ammonia oxidation, it is shown that systematic application of sensitivity analyses of premixed flames under typical gas-turbine combustion conditions reduces the description to 12 elementary steps for hydrogen oxidation, 4 of them being reversible, and an additional 19 steps for ammonia oxidation, 6 of them being reversible, yielding reasonable predictions for auto-ignition and deflagration processes. Subsequent introduction of steady-state approximations for chemical intermediates, afforded by the high-pressure conditions existing in gas-turbine combustion chambers, effectively reduces the fuel-oxidation description in systems utilizing H 2 -NH 3 fuel mixtures to two global steps for deflagrations, namely, 2H 2 + O 2 ⇌ 2H 2 O and 4NH 3 ＋ 3O 2 ⇌ 2N 2 + 6 H 2 O. Analytical expressions for the associated overall rates, involving the local temperature and the O 2 , H 2 , NH 3 , N 2 , and H 2 O concentrations, are derived through selective truncation of the steady-state expressions, resulting in a simplified chemistry description that can facilitate future numerical analyses based on direct-numerical and large-eddy simulations. Novelty and significance statement A new short mechanism involving only 31 elementary reactions between 16 reactive species has been derived for hydrogen-ammonia oxidation under conditions of pressure, temperature and dilution typically found in gas-turbine burners. Introduction of steady-state assumptions for all intermediate species leads to a two-step mechanism that is shown to predict burning rates with sufficient accuracy. The proposed mechanism can significantly reduce computational times in future direct-numerical and large-eddy simulations.