Computational Investigation of Hydrogen-Air Mixing in a Large-Bore Locomotive Dual Fuel Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">The internal combustion engine (ICE) has long dominated the heavy-duty sector by using liquid fossil fuels such as diesel but global commitments by countries and OEMs to reduce lifecycle carbon dioxide (CO₂) emissions has garnered interest in alternative fuels like hydrogen. Hydrogen is a unique gaseous fuel that contains zero carbon atoms and has desired thermodynamic properties of high energy density per unit mass and high flame speeds. However, there are challenges related to its adoption to the heavy-duty sector as a drop-in fuel replacement for compression ignition (CI) diesel combustion given its high autoignition resistance. To overcome this fundamental barrier, engine manufacturers are exploring dual fuel combustion engines by substituting a fraction of the diesel fuel with hydrogen which enables fuel flexibility when there is no infrastructure and retrofittability to existing platforms. This work studies the implications of mixing port-injected hydrogen fuel in a large-bore rail engine operating with hydrogen-diesel dual fuel combustion. Previous work was done to validate a single-cylinder computational model to data collected on this engine when operating with dual fuel combustion of natural gas and diesel. This model was then modified to employ gaseous hydrogen as the port injected fuel. First, a grid sensitivity study was performed, and it was concluded that the computational mesh was refined enough to minimize numerical error. Modeling implications are then investigated by comparing two RANS turbulence models in terms of their prediction of turbulent mixing predictions of hydrogen and air. It was seen that both had minimal differences in bulk mass flow trends, but choice of RANS turbulence model could impact qualitative predictions of fuel-air stratification. Lastly, hydrogen injection timing and flow rate were varied, and it was concluded that the highest injection flow rate is best for both premixing hydrogen with air and reducing hydrogen mass left in the intake. Additionally, given the potential limitations of hydrogen injection pressure, injection timing can be advanced to allow more time for mixing when injection velocity is maximized.</div></div>