Study of Performance and Combustion in Ammonia-Fueled CI Engines via Diesel Simultaneous Injection

Ammonia is a promising carbon-free hydrogen-carrier with wide industrial availability, yet its low flame speed, high latent heat, and narrow flammability pose challenges for compression ignition engines. This study investigates ammonia–diesel dual-fuel operation at 50% and 80% loads, with diesel injection pressures varied from 200 to 340 bar, and ammonia energy shares (AES) ranging from 0% to 40% to observe the sustainability of ammonia fuel in light-duty engines. Experimental results show that increasing injection pressure enhanced cylinder pressure by up to 10% at low AES and advanced peak pressure timing, partially compensating for ammonia’s slow combustion. The heat release rate (HRR), delayed by 5–9°CA with increasing AES, was improved at higher injection pressures, with HRR peaks shifting to the controlled combustion phase. Ignition delay increased with AES, reaching 4.5°CA at 40% ammonia at 200 bar compared to diesel at 320 bar, but was reduced to 2.78°CA at an injection pressure of 320 bar. Cycle-to-cycle variations, quantified by CoV _imep , rose with AES due to prolonged combustion but decreased by up to 27% with optimized injection pressure. However, at 40% AES, stability improvement plateaued at 300 bar. Brake-specific fuel consumption (BSFC) increased by up to 48% at high AES, while higher load and injection pressure partially mitigated the rise. Despite increased fuel consumption, operating costs remained relatively low, increasing by ₹3.3/kWh at 50% load and ₹1.3/kWh at 80% load for 40% AES. The results indicate that electronically controlled high-pressure ammonia injection combined with higher compression ratios can enhance combustion quality, improve thermal efficiency, and reduce the effective fuel cost in ammonia–diesel dual-fuel engines.