Guided Port Injection of Hydrogen as an Approach for Reducing Cylinder-to-Cylinder Deviations in Spark-Ignited H2 Engines – A Numerical Investigation

The reduction of anthropogenic greenhouse gas emissions and ever stricter regulations on pollutant emissions in the transport sector require research and development of new, climate-friendly propulsion concepts. The use of renewable hydrogen as a fuel for internal combustion engines promises to provide a good solution especially for commercial vehicles. For optimum efficiency of the combustion process, hydrogen-specific engine components are required, which need to be tested on the test bench and analysed in simulation studies. This paper deals with the simulation-based investigation and optimisation of fuel injection in a 6-cylinder PFI commercial vehicle engine, which has been modified for hydrogen operation starting from a natural gas engine concept. The focus of the study is on a CNG-derived manifold design which has been adapted with regard to the injector interface and is already equipped with so-called gas injection guiding tubes for targeted fuel injection in front of the intake runners of the individual cylinders. Significant deviations between the averaged cylinder pressure profiles of the individual cylinders observed on the test bench point to an issue with the equal distribution of the fuel supply to the individual cylinders. A subsequent 3D CFD simulation of the internal manifold flow showed geometry-induced turbulence of the fresh air flow in the area of the hydrogen supply outlet of several cylinders, which can lead to variations in cylinder-specific fuel quantities. In order to minimise the influence of the air flow in the manifold on the fuel injection, a dedicated injection guide concept for the gas injection tubes in the intake manifold has been designed with the aim of moving the position of hydrogen injection closer to the intake valves. In this study, this concept is analyzed based on first results obtained from a detailed 3D CFD simulation, especially in terms of the uniformity of hydrogen distribution between the cylinders, mixture formation and the effect on combustion.