Knock Inhibition in Hydrogen Fueled Argon Power Cycle Engine with a Higher Compression Ratio by Water Direct Injection at Late Exhaust Stroke

Hydrogen-fueled Argon Power Cycle engine is a novel concept for high efficiency and zero emissions, which replaces air with argon/oxygen mixtures as working fluid. However, one major challenge is severe knock caused by elevated in-cylinder temperature resulting from high specific heat ratio of Argon. A typical knock-limited compression ratio is around 5.5:1, which limits the thermal efficiency of Argon Power Cycle engines. In this article, preliminary experimental research on the effect of water direct injection at late exhaust stroke is presented at 1000 r/min with IMEP ranging from 0.3~0.6 MPa. Results show that, with temperature-reducing effect of water evaporation, knock is greatly inhibited and the engine can run normally at a higher compression ratio of 9.6:1. Water injected at the exhaust stroke minimizes its reducing effect on the specific heat ratio of the working fluid during the compression and expansion strokes. Thus, the maximum net indicated thermal efficiency reaches 50.32% when Ar/O₂ molar ratio is 90:10 and equivalence ratio is 0.38. Besides, the anti-knock capability is most effective with a water injection timing later than 250°CA ATDC. The highest net indicated thermal efficiencies are obtained with water injection timing from 260 to 280°CA ATDC. Additionally, the water produced through combustion and the water needed for injection are in the same order of magnitude, namely tens of milligrams each cycle. Therefore, only a small tank will be needed as a buffer, if water can be separated and collected from the exhaust gas. This paper suggests that water injection is a feasible method for knock inhibition in the Argon Power Cycle engine.