Ammonia and Ammonia/Hydrogen Mixtures Ignition Delay Times and Chemical Kinetic Model Validation at Gas Turbine Relevant Conditions

Abstract Undiluted mixtures of ammonia/hydrogen (NH3/H2) were auto-ignited inside the University of Central Florida’s high-pressure shock tube, allowing for lower temperature ignition data and realistic fuel concentrations to be experimentally tested and compared to chemical kinetic models. 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 2018 Glarborg et al. model, which contains nitrogen-based chemistry and was previously validated at lower pressures and dilute conditions. The 20 bar experimental IDT data is predicted well by the model, but large deviations were shown for 5 and 10 bar with hydrogen addition. Experimental 5 bar IDTs were measured to be faster than the 10 and 20 bar data, highlighting the unique combustion chemistry of the hydrogen explosion limits. The model failed to capture explosion limit properties at intermediate pressures, where hydrogen pressure-dependence reaction chemistry is prominent. A sensitive 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 2018 Glarborg et al. model predictions of the hydrogen explosion limits. Furthermore, an improved chemical kinetic model is shown built upon the experimental data. By improving chemical kinetic models, air-breathing hydrogen/ammonia turbine combustor efficiencies can be improved, and nitrogen oxide (NOx) emissions can be lowered to ultimately reduce greenhouse emissions.