Effect of Ar mass ratio and mixture equivalence ratio on the integrated hydrogen argon power cycle

This paper investigates hydrogen combustion in an argon–oxygen (Ar–O₂) environment for compression ignition engine applications using computational fluid dynamics (CFD). The numerical framework is validated through two independent datasets: experimental results from Sandia National Laboratories and hydrogen jet ignition experiments conducted in an Ar–O₂ atmosphere, establishing confidence in the predictive capability of the model. A parametric analysis is performed to evaluate the effects of excess air ratio (λ) and argon mass fraction on ignition characteristics, combustion efficiency, and engine performance. The results indicate that operating under lean conditions improves combustion efficiency but leads to a substantial reduction in engine load. Increasing the argon mass ratio enhances engine thermal efficiency, primarily due to the higher specific heat ratio of argon, which improves the thermodynamic efficiency of the cycle. However, elevated argon concentrations significantly reduce combustion efficiency as a result of limited oxygen availability, leading to increased levels of unburned hydrogen. The analysis further reveals that ignition delay is influenced not only by temperature at the start of injection, but also by Ar mass ratio, highlighting the coupled thermodynamic effects governing hydrogen autoignition in diluted environments. Overall, unburned hydrogen is identified as a critical bottleneck for the practical implementation of compression ignition hydrogen engines operating in Ar–O₂ mixtures.