As part of the fight against global warming and to achieve greenhouse gas emission targets set by the different COP agreements, it is crucial to reduce the carbon footprint of ground transportation. Indeed, mobility needs are continuously growing with increase in population in urban areas. 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 aim is to investigate and understand the influence of the hydrogen specificities on the different physical phenomena taking place in an ICE. The paper will present results obtained both on light-duty and heavy-duty engine configurations.
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. These experiments allowed to make several observations on the engine behavior and to list the requirements to operate a hydrogen fueled engine: compression ratio, tumble level, valve actuation strategies, dilution methods etc.
The gas-gas injection was experimentally studied in the High Pressure/High Temperature vessel available at IFPEN. Different optical diagnostics were implemented to observe the hydrogen jet evolution and provide qualitative and quantitative information on the jet behavior and the mixing evolution. Those measurements were used to calibrate the 3D CFD numerical approach and to adapt the methodology to get a realistic modeling of the hydrogen injection and of the mixture preparation.
Based on a 0D pre-study (boundary conditions) and using the injection modelling 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, including air fluid motion, compression ratio and general settings (piston shape, injector and spark plug positions).
