3D CFD Simulations of Hydrogen Engine Combustion

Abstract: With the trend of decarbonization, the transport sector is exploring possibilities of fossil fuel free solutions. Hydrogen can be a potential fuel for future engine applications. In this work, the concept of H2 HPDI is investigated, where a pilot diesel injection ignites the hydrogen jet. This solution may enable low carbon emission and high energy efficiency. 3D CFD simulation is performed using CONVERGE. Fuel temperature, wall temperature, fuel injection timings, swirl ratio and kinetic mechanisms are studied to calibrate the model. The models is validated against experiment results at mid-load conditions. Then, varied mass of pilot diesel is studied and results show that as low as 0.5% energy share in the pilot diesel are sufficient to trigger H2 ignition. To further eliminate the carbon emission, the possibility of using H2 as the only fuel at mid-load conditions is studied. Due to the high autoignition temperature of H2, solutions like inlet preheating and H2 pilot injection are applied to provide the high temperature to achieve H2 combustion near TDC. Simulation results show that significant inlet preheating is needed and 60 K increase at IVC is needed for H2 combustion. With this solution, lower closed-cycle efficiency is observed due to high heat losses. As for pilot H2 combustion, with 5% energy share in the pilot H2, mixing-controlled combustion of H2 can be observed with only 15 K increase in the IVC temperature. Comparable efficiency to engines with pilot diesel injections can be observed while NOx emission increases due to higher flame temperature of H2 combustion. Finally, the work connected to H2 direct injection is investigated. Due to the large number of moles of gas injected near TDC, additional work as high as 2.7% of the fuel energy can be achieved.