The 3D-CFD Contribution to H 2 Engine Development for CV and Off-Road Application

The hydrogen engine is one of the promising technologies that enables carbon-neutral mobility, especially in heavy-duty on- or off-road applications. In this paper, a methodological procedure for the design of the combustion system of a hydrogen-fueled, direct injection spark ignited commercial vehicle engine is described.In a preliminary step, the ability of the commercial 3D computational fluid dynamics (CFD) code AVL FIRE Classic to reproduce the characteristics of the gas jet, introduced into a quiescent environment by a dedicated H2 injector, is established. This is based on two parts: Temporal and numerical discretization sensitivity analyses ensure that the spatial and temporal resolution of the simulations is adequate, and comparisons to a comprehensive set of experiments demonstrate the accuracy of the simulations. The measurements used for this purpose rely on the well-known Schlieren technique and use helium as a safe substitute for H2. They reveal how the jet properties depend on the ratio between injection and ambient pressure and how the jet can attach to the chamber roof or be focused depending on the exact position of the injector within its bore.The numerical recipe validated using the Schlieren measurements is then adapted for the calculation of the mixture formation in the engine combustion chamber. The investigations encompass variations of the degree of recess within the injector bore, starting with the default flush-mounted configuration, and different piston design concepts. Key performance indicators of the simulations are the interaction between injection and engine charge motion and the development of the mixture homogeneity. Test bench results such as exhaust emissions are correlated to the numerical output provided by the simulations.