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As part of the fight against global warming and to achieve greenhouse gas emission targets, it is crucial to reduce the carbon footprint of ground transportation. Mobility needs are continuously growing with increase in population. All these factors will lead to an upsurge in the energy demand for the mobility in the very next future. Consequently, the diversification of low carbon energy sources is urgently required. Hydrogen can be used for mobility solution in its two energy conversion mechanisms: The Fuel Cell technology or the Internal Combustion Engine (ICE). The latter option, studied in the present work, offers the advantages of current fossil fuel engines – existing and proven technology, lifetime, controlled cost – with a very low carbon footprint. The overall objective of the study is to define the specifications of a dedicated Hydrogen direct injection combustion system for ground transportation application with the best fuel efficiency and lower raw emissions, to minimize the aftertreatment needs. A complete experimental and numerical study was carried out to get valuable information on various phenomena occurring throughout the engine cycle. The very first step of the study consisted in performing experimental investigations. For this purpose, an all metal single cylinder engine originally designed for gasoline spark ignited combustion (tumble air motion, gasoline direct injection) was modified for hydrogen direct injection combustion. The gas-gas injection was experimentally studied in the High Pressure/High Temperature vessel available at IFPEN. Those experiments were used to calibrate the 3D CFD numerical approach. Based on a 0D pre-study (boundary conditions) and using the injection modeling calibration introduced before, 3D CFD simulations have been then carried out with specific hydrogen kinetics properties. Finally, this comprehensive study highlights the specificities of ICE running with hydrogen. It provides indications and guidelines for further developments and optimization of hydrogen combustion engines.

A Large-Eddy Simulation (LES) modeling framework, dedicated to ultra-lean spark-ignition engines, is proposed and validated in the present work. A direct injection research engine is retained as benchmark configuration. The LES model is initially validated using the cold gas-exchange conditions by comparing numerical results with PIV (Particle Imaging Velocimetry) experimental data. Then, the fired configuration is investigated, combining ECFM (Extended Coherent Flame Model) turbulent combustion model with Adaptive Mesh Refinement (AMR). The capability of the model to reproduce experimental pressure envelope and cycle-to-cycle variability is assessed. Within the major scope of the work, a particular focus on the Combustion Cyclic Variability (CCV) is made correlating them with the variability encountered in the in-cylinder aerodynamic variations. R3P4. Finally two post-processing tools, Empirical Mode Decomposition (EMD) and Γ3p function, are proposed and combined to analyse for the first time the aerodynamic tumble-based in-cylinder velocity field. Both tools make it possible to get deeply into the insight and visualization of the flow field and to understand the links between its cyclic variability and the combustion cyclic variability.