Undiluted Ignition Delay Times of Ammonia/Hydrogen/Synthetic-Air Mixtures at Gas Turbine Conditions

Abstract Undiluted mixtures of ammonia/hydrogen (NH3/H2) were auto-ignited inside a high-pressure shock tube, allowing for lower temperature ignition data and realistic fuel concentrations to be experimentally tested and compared to chemical kinetic mechanism predictions. Ignition delay time (IDT) measurements were collected at the conditions relevant to power generation gas turbines (5-20 bar, 1000-1700 K) and across a range of equivalence ratios (0.5-1.5). The data was compared against the predictions of recent chemical kinetic mechanisms, most validated at lower pressures and dilute conditions. Experimental IDTs at 5 bar were measured to be faster than the 10 and 20 bar data, highlighting the unique combustion chemistry of the hydrogen explosion limits. The mechanisms predicted the 20 bar experimental IDT data well, but large deviations were shown for 5 and 10 bar with hydrogen addition. The mechanisms failed to capture explosion limit properties at intermediate pressures, where hydrogen pressure-dependence reaction chemistry is prominent. A sensitivity analysis was performed to investigate the top reaction pathways predicted by the model, and the chain branching reactions H + O2(+M) → HO2(+M) and HO2 + H → 2OH are suggested as key reactions to reinvestigate to improve the literature mechanism predictions. Furthermore, we show that the predictions can be improved based on reaction rate improvements by updating reaction rates for key reactions.