Experimental investigation and optimization of ammonia–hydrogen chemical kinetics with ignition delay times from shock tubes

A combined experimental and numerical approach investigates the ignition delay times of ammonia–hydrogen mixtures in oxygen or synthetic air measured in shock tubes under different dilutions with argon and nitrogen. A series of novel ignition delay time measurements is presented for stoichiometric fuel–air mixtures diluted 1:10 and 1:5 in argon as well as 1:2 in nitrogen at the shock tube facility of the German Aerospace Center (DLR). The initialized gas conditions behind the reflected shock waves range between 940–2200 K and 4–16 bar. Additionally, recent ignition delay time determinations of fuel–air mixtures without subsequent dilution from the shock tube facility of the University of Central Florida (UCF) are reevaluated. Experimental data sets are analyzed with the application of multiple chemical kinetic models. The study reveals deficiencies in the modeling of fuel-oxidizer mixtures with relatively low dilution, representative for real combustion applications. To improve the chemical kinetic modeling capabilities, the reaction model DLR Concise is updated with new insights from literature. Subsequently, the updated model is optimized with the new experimental data and additional data on ignition delay times available from literature. 373 ignition delay times of ammonia and its mixture with hydrogen are targeted for the optimization. The linear transformation model is applied to optimize the most sensitive N-chemistry reactions within their uncertainties. The new experimental data from DLR confirm the observed deviations between the reevaluated experimental data from UCF and established chemical kinetic models. The updated and optimized DLR Concise models are resolve these modeling deficiencies and consistently reproduce the new and reevaluated data from both shock tube facilities. The optimized reaction model consistently reproduces the complete targeted experimental data with a broad range of initial temperature, pressure and mixture boundary conditions. Thus, the model can reliably be applied for numerical investigations of internal combustion engine ignition processes.