A parametric study of high-pressure direct injections of hydrogen in an argon–oxygen environment by using large-eddy simulation and tabulated chemistry

Within the context of a global de-carbonization, hydrogen plays a significant role in the transition to low-carbon activities. In particular, the Argon Power Cycle (APC) is an engine concept that circulates argon in a closed-loop configuration, burning only hydrogen and oxygen and thus rendering a zero-emissions system. The work at hand aims to provide a first step towards accurate and affordable modelling of such an engine in the high-pressure direct-injection (HPDI-H₂) configuration. Using the large-eddy simulation (LES) technique, coupled with a novel tabulated chemistry approach (HR-FGM), several injections of hydrogen at high pressure in an argon–oxygen atmosphere are simulated. More in detail, parametric studies on relevant engine parameters (injection pressure, nozzle diameter, ambient pressure, ambient temperature and ambient oxygen level) are carried out and analysed in terms of ignition delay, flame dynamics and heat release rate. The corresponding results represent valuable insights into the APC combustion process and its modelling. In particular, it is found that: (a) the ignition delay is strongly sensitive to the ambient temperature, but not to the other investigated parameters, (b) the total heat release increases with the injection pressure and the nozzle diameter (and, to a lesser extent, with the ambient oxygen concentration), but the instantaneous fraction of fuel that is converted into heat decreases with increasing nozzle diameter and decreasing injection pressure, (c) OH concentration might not be a good indicator of the mass burning rate in auto-igniting hydrogen flames.