Numerical study of non-premixed hydrogen combustion in an argon power-cycle engine

The hydrogen-fueled direct-injection (DI) compression-ignition (CI) argon power cycle (APC) is a highly efficient and emission-free energy conversion system that relies on the low specific heat capacity of the working fluid argon. Compared to conventional internal combustion engines, the DI CI APC allows to easily adjust the oxygen level of the charge. Besides, the engine operating pressure can be increased at virtually no cost assuming the mechanics of the engine are suitable. In this study, we systematically investigate how to take advantage of these two benefits by varying the intake pressure and oxygen mole fraction using a validated Reynolds-averaged numerical simulation environment. It is found that the optimal amount of oxygen is a trade-off between burn duration and specific heat ratio of the charge. Provided that the oxygen mole fraction is high enough to achieve complete combustion, the sensitivity of thermal efficiency to oxygen mole fraction is relatively low. Increasing the intake pressure for a fixed oxygen level leads to shorter burn durations and less heat loss, thereby significantly increasing thermal efficiency. Flame-wall interaction is a dominant factor that negatively impacts the engine performance, and should therefore be minimized. The highest obtained thermal efficiency is 70 %, which is comparable to but mostly higher than efficiencies of state-of-the-art hydrogen fuel cells. The DI CI APC has therefore potential to overcome challenges of conventional engines, without penalizing its strengths. • Computational fluid dynamics simulations of a novel argon engine are performed. • Insights are gained in non-premixed hydrogen combustion process. • Effect of oxygen level and operating pressure on engine performance are studied. • Key insights in how to enhance thermal efficiency are identified.