Hydrogen may be used to feed a fuel cell or directly an internal combustion engine as an alternative to current fossil fuels. The latter option offers the advantages of already existing hydrocarbon fuel engines - autonomy, pre-existing and proven technology, lifetime, controlled cost, existing industrial tools and short time to market - with a very low carbon footprint and high tolerance to low purity hydrogen. Hydrogen is expected to be relevant for light and heavy duty applications as well as for off road applications, but currently most of research focus on small engine and especially spark ignition engine which is easily adaptable. This guided us to select modern high-efficient gasoline-based engines to start the investigation of hydrogen internal combustion engine development.
This study aims to access the properties and limitations of hydrogen combustion on a high-efficiency spark ignited single cylinder engine with the support of the 3D-CFD computation.
A high efficiency gasoline single cylinder engine was adapted for hydrogen combustion system with a direct injection and a platinum-free cold spark plug. The injection and camshaft phasing ranges were defined to limit the passage of hydrogen in the intake and exhaust manifolds. The experiments were focused on two operating points (2000rpm and 3000rpm at IMEP=10 bar) at various fuel-air equivalent ratios, fuel injection and air intake camshaft timings and in-cylinder charge motion, at high compression ratio (CR=14). 3D-CFD computation was carried out on CONVERGETM to visualize and understand the local mixing in the combustion chamber.
The study revealed that the highest indicated efficiency (close to 47%) coupled with low NOX and acceptable unburnt H2 emissions (respectively below 0.5g/kWh and 1% input energy) was obtained at lean mixture, early hydrogen injection and high tumble level. The pre-ignition known as one of the highest challenges in hydrogen combustion is successfully limited by adjusting the injection timing and camshaft phasing. 3D-CFD simulations showed that optimum fuel injection and intake camshaft timings should favor the homogenization of the mixture and avoid the presence of rich zones near hot spots to avoid pre-ignition.