Auto-igniting and combusting high-pressure hydrogen injections in air and argon–oxygen environments

Using hydrogen in an internal combustion engine holds the potential for sustainable and carbon-free energy production, but is typically plagued by nitrogen oxides emissions. An Argon Power Cycle would remove the nitrogen from the cycle and has the potential to substantially enhance the thermal efficiency of an engine by a higher ratio of specific heats of the working fluid. Using an optically-accessible constant-volume preburn chamber, equipped with a standard gasoline injector for injecting hydrogen, the effects of the ambient composition, temperature, and oxygen content on the development, auto-ignition and combustion of hydrogen injections are investigated. Using high-speed pressure transducers, Schlieren and OH ∗ chemiluminescence, the jet development and combustion of hydrogen injections is investigated. The rate of heat release reveals differences in burn duration, and premixed and mixing-controlled combustion modes, all depending on the ambient conditions. The results indicate that the hydrogen jets mix less well in argon–oxygen environments than in air at otherwise similar conditions, while the ignition delay and burn duration are similar at ambient temperatures above 1100 K and oxygen contents above 10%. The rate of heat release is almost always lower in argon–oxygen ambients than in air at similar conditions, while the pressure increase due to combustion can be more than 50% higher in argon–oxygen environments for ambient conditions that give rise to mixing-controlled combustion. Novelty and significance The novelty of the present study lies in the focus on auto-ignition behavior of hydrogen under a wide variety of ambient conditions relevant for CI engines using both air and argon–oxygen ambients. As oxygen is continuously added in such an argon power cycle, a trade-off between increased oxygen mixing rates and a higher ratio of specific heat is investigated in detail. Using argon implicates higher ambient temperatures at identical compression ratios, shifting focus for auto-ignition behavior at elevated temperatures. Additionally, this study compares the OH* radical luminescence results to the “typical” pressure derived combustion parameters.