Synergistic optimization of combustion chamber design and hydrogen injection strategies for ultra-lean combustion in hydrogen engines

Abstract

Hydrogen, as a renewable zero-carbon fuel, is an ideal alternative to internal combustion engine fuels. The paper numerically investigates the effect of piston geometry on lean combustion in hydrogen engines, focusing on early and late injection strategies. Two novel piston bowl designs, referred to as the right-concave piston and left-concave piston, were analyzed for their interaction with hydrogen jets during mixture formation and combustion processes. Validation of the numerical outputs were conducted using an experimental testbench. Results reveal that the right-piston had a stronger and larger scale tumble, compared to the flat-top piston, facilitating hydrogen diffusion. However, due to their early injection timing, mixture distribution at ignition timing was relatively uniform, resulting in comparable indicated thermal efficiency (ITE) and NOx emissions. Conversely, the left-concave piston demonstrated inferior ITE and higher emissions under single injection but achieved superior performance with an optimized dual injection strategy. This strategy improved mixture stratification increased thermal efficiency, and significantly reduced NOx emissions. The key findings highlight the critical role of piston geometry and injection strategy in optimizing hydrogen combustion engines for higher efficiency and lower emissions.