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To understand the effect of hydrogen addition on the auto-ignition of ammonia at high temperatures, ignition delay times of stoichiometric ammonia/hydrogen blends were measured in a shock tube at temperatures from 1020 to 1945 K, pressures of 1.2 and 10 atm, and hydrogen fractions from 0% to 70%. The measured ignition delay times were compared with seven available kinetic models. Chemical kinetic analyses were performed using both the Glarborg Model and Otomo Model to interpret the interactions between ammonia and hydrogen during the high temperature auto-ignition. Experimental results show that ammonia ignites slower than hydrogen, and hydrogen addition can reduce the ignition delay time nonlinearly. The numerical analysis identifies that 5% hydrogen addition does not significantly affect the reaction flux of ammonia at 20% fuel consumption, however, it makes the fuel H-atom abstraction reaction NH3 + H NH2 + H2 proceed in the reversed way at the initial stage of ignition, therefore generate active H radical for further chain branching and promote the reactivity.

Impact of water (H2O) vitiation on auto-ignition characteristics of kerosene/air mixtures was investigated behind the reflected shock waves covering pressures of 0.45–7.5 atm and temperatures of 900–1450 K. Arrhenius-type expressions were fitted for both mixtures with and without H2O using multiple linear regression method. Temperature- and pressure-dependences of ignition delay times were experimentally observed to be in-line with conventional hydrocarbons for all the test mixtures, but stronger pressure-dependence exhibited when presence of H2O. A four-component surrogate model fuel (25.7% n-tetradecane/23.0% 2-methylundecane/42.1% n-butylcyclohexane/9.2% n-butylbenzene) was proposed based on similarity criterion of function group. A surrogate mechanism was subsequently assembled by incorporating the modified rate rule of certain reaction class. The proposed kinetic model reproduces well the experimental observations at the entire conditions. Thermal and kinetic effects of H2O on the RP-3 reactivity were distinguished by factitiously inducing a weak collision H2O* and an inert H2O**. Results reveal that the kinetic-based promotion of H2O outweighs the thermal-based inhibition on the RP-3 reactivity at high pressures due to higher collision efficiency, which facilitates the reaction H2O2 (+M) ⟺ OH + OH (+M). However, the RP-3 reactivity is inhibited only by thermodynamics without kinetics at low pressures.