This paper presents an experimental and numerical study of a directly injected, spark-ignited (DI SI), heavy duty hydrogen fueled engine at knock-limited conditions. The impact of air-fuel ratio and ignition timing on engine performance is first investigated experimentally. Two-zone combustion modeling of the hydrogen fueled cylinder is then used to infer burn profiles and unburned, end-gas conditions using the measured in-cylinder pressure traces. Simulation of the autoignition chemistry in this end-gas is then undertaken to identify key parameters that are likely to impact knock-limited behavior.
The experiments demonstrate knock-limited performance on this high compression ratio engine over a wide range of air-fuel ratios, λ. Other trends with λ are qualitatively similar to those shown in previous studies of hydrogen fueled engines. Kinetic simulations then suggest that some plausible combination of residual nitric oxide from previous cycles and locally high charge temperatures at intake valve closing can lead to autoignition at the knock-limited conditions identified in the experiments. This prompts a parametric study that shows how increased λ makes hydrogen less likely to autoignite, and suggests options for the design of high efficiency, directly injected, hydrogen fueled engines.