Numerical analysis of the direct injection and combustion processes in a spark ignition hydrogen internal combustion engine

In the current context of actions needed to counter climate change, the continuous tightening of CO₂ and criteria pollutant emissions limits is considered to be a pivotal challenge to the mobility sector. Different potential technological solutions are being explored to face this scenario. The vast research area ranges from the implementation of electrification in powertrains, also considering exclusively electrified ones, to the continuous development of the internal combustion engine (ICE) hardware. Focusing on the latter, among the technological solutions investigated, different fuel typologies are currently under examination to substitute fossil-derived fuels. In this environment, hydrogen is recognized to be particularly interesting, thanks to its combustion properties: high flame propagation speed and wide flammability range, which allow lean combustion, and good knock resistance. However, its low density and high diffusivity imply that the evolution of the in-chamber injection process is well controlled to obtain the best possible mixture conditions at the spark plug surroundings to guarantee relevant efficiency and power levels minimizing nitrogen oxides (NOx) emissions. In this context, the present study aims to analyze the potentialities of a direct injection hydrogen-fueled internal combustion engine. The engine in exam was derived from a 6-cylinder, 3 L diesel engine, equipped with a new dedicated piston bowl according to the results obtained from previous studies. First, the activity focused on the simulation and analysis of the injection and combustion processes of a set of operating points in a 3D-CFD environment by means of the CONVERGE CFD software. After that, the results, analyzed to understand the effect of different injection timings and lambda values on the mixture homogenization and the combustion process, allowed the calibration of a turbulence model and subsequently of a predictive combustion model (SI-Turb) in a 1D-CFD environment using the GT-SUITE software. Eventually, the calibrated combustion model was extended to the complete engine model and its performances were analyzed to better understand the charge stratification phenomena under different operating conditions.