High Pressure Hydrogen Injector Sizing Using 1D/3D CFD Modeling for a Compression Ignition Single Cylinder Research Engine 2024-01-2615
With the aim of decarbonizing the vehicles fleet, the use of hydrogen is promising solution. Hydrogen is an energy carrier, carbon-free, with high calorific value and with no CO2 and HC emissions burning in ICE. Hydrogen use in spark ignition engines has already been extensively investigated and optimized. On the other hand, its use in compression ignition engines has been little developed and, therefore, there is a lack of information regarding the combustion in ultra-lean conditions, typical of diesel engines.
Several applications employ dual fuel combustion for the easy management of the PFI injection system to be applied in addition to the DI Common Rail system. However, this mode suffers from several problems regarding the management of the maximum flow rate of hydrogen into the intake. In particular, to avoid throwing hydrogen into the exhaust, injection must be started after the valve crossing. Furthermore, it is not possible to introduce gaseous fuel into the engine when the compression phase begins. In fact, the hydrogen can find favorable autoignition conditions, giving rise to unwanted combustion processes in the manifold.
For these reasons, a direct hydrogen injection system that could be easily applied to the head of the production engine has been designed and realized. In the head of 1.9l GM engine mounted on a single cylinder research engine, the adapter in place of the pre-heating glow plug has been modified to accommodate a commercial injector for the hydrogen direct injection up to 100 bar. Hydrogen is provided by a bottle at 200 bar via a secured line and a rail prior to reach the injector.
In the design stage, attention has been paid to the correct assessment of the optimum diameter of the injection system. A 1D Fanno flow based model has been developed to determine in a quick way the mass flow rate and total pressure losses for several possible diameters. In particular, in order to have the desired hydrogen quantity entering into the cylinder a probe featured by a diameter of 2 mm and length of 137 mm has been identified. To confirm the validity of the 1D result, the CAD model of injection system has been designed and analyzed by means of computational fluid-dynamic simulations, which have shown a good agreement with the 1D outcomes. Thus, the 1D Fanno model can be considered a fast and reliable tool for the preliminary design of injection systems for gaseous fuels.
