Simulation Study of the Modified Combustion Chamber Effect on Ammonia-Diesel Dual-Fuel Engine Performance

The application of low-carbon/carbon-free fuel engines to transportation is an important way to achieve energy saving and emissions reduction in conventional engines. In this study, with the help of computational fluid dynamics (CFD) simulation software, the effect of ammonia energy ratio (AER) on ammonia-diesel dual-fuel (ADDF) engine performance was investigated in a diesel engine, then a modified combustion chamber without a traditional squish area was proposed and investigated to improve the ammonia combustion. The results indicated that the low flame propagation speed and high ignition temperature of ammonia negatively impact the performance of the ADDF engine. At an AER of 60%, the ADDF engine’s indicated thermal efficiency (ITE) increased by 0.2%, and greenhouse gas (GHG) emissions decreased by 22.3%, compared to the pure diesel mode in the original chamber. Unburned ammonia emissions increased with the rise in AER. In ADDF mode, the modified combustion chamber, compared to the original design, enhanced ammonia combustion and improved the performance of the ADDF engine within the 40%–60% AER range. When the AER exceeded 60%, the amount of diesel fuel injected decreased, making it difficult to ignite ammonia in the modified combustion chamber, resulting in reduced engine performance. In ADDF mode, the modified combustion chamber increased the ITE by 2% and reduced GHG emissions by 23% compared to the original combustion chamber at 60% AER. Targeted improvements to the shape of the combustion chamber can enhance the performance of ADDF engines and reduce GHG emissions.