Effect of Equivalence Ratio on Combustion Characteristics in a Hydrogen Direct-Injection SI Engine

Gases such as hydrogen are regarded as promising alternative fuels for improving the energy efficiency and reducing the greenhouse gas emissions of conventional internal combustion engines. Hydrogen spark-ignition (SI) engines based on direct injection (DI) promise significant advantages in terms of thermal efficiency and power output, as well as a means of overcoming problems related to knocking, backfiring, and pre-ignition. A better understanding of the effect of the hydrogen jet on the concentration distribution and mixing process in a DISI engine should provide new and useful insights into combustion optimization. The objective of the present work is to gain a deeper comprehension of the characteristics of late-injection hydrogen combustion. An experimental combustion setup is applied to a fired, jet-guided DISI engine operated at 600 rpm in tail ignition (TI) injection mode. A high-speed camera, synchronized with the spark, is focused on a field of view with a diameter of 52 mm through a window at the bottom of the piston crown. A series of single-shot images, captured in different intervals, is used to study the time evolution of the flame distribution. Variations of the equivalence ratio at tail ignition mode combustion are found to impact the development of the early flame, as well as the flame propagation.