Numerical Study of the Hydrogen/Air Mixing in a High Performance 2 Stroke Opposed Piston Engine

<div class="section abstract"><div class="htmlview paragraph">Hydrogen as a fuel for internal combustion engines is the most promising candidate for the achievement of the zero-emissions target fixed by the European institutions for sports car applications. The development of a high-specific-power hydrogen engine is not trivial considering the low volumetric energy density of hydrogen. Furthermore, the necessity to reduce the engine encumbrance in favour of on-board fuel storage makes alternative engine architectures, such as the two-stoke opposed-piston design, particularly attractive.</div><div class="htmlview paragraph">A numerical study is conducted to evaluate the potential of such architecture. First, the overall engine is simulated in a 1D-CFD framework assuming a fully homogeneous hydrogen/air mixture. Then, the intake and exhaust port phasing are optimized, and a 3D CAD model of the cylinder is developed based on the defined parameters. 3D-CFD simulations of the scavenging process are performed and employed to tune the 1D model. Starting from a single point injection configuration, the simulations predict inhomogeneous mixture formation. This finding suggests that the hydrogen/air mixing process could be a critical aspect to be improved to reach the performance and efficiency targets. An extensive 3D-CFD study is then performed analysing the impact on mixture formation and combustion evolution/efficiency of the hydrogen injector location, orientation and injection phasing with the final aim to define design guidelines for the development of this new engine technology. To improve the mixture homogeneity an innovative multi-point injection ring is designed, virtually implemented and tested. This multi-point injection system proves effective in enhancing mixture homogeneity, which, although not ideal, is sufficient to achieve the combustion duration required for the target efficiency. The results of the current study confirm the feasibility of the proposed engine architecture and its potentiality in terms of performance and efficiency, as highlighted by the 1D simulations of the overall engine.</div></div>