Gene Expression Programming Optimization of Pilot Injection Parameters in CRDI Hydrogen–Biofuel Engines

Abstract This study investigates the effects of fuel injection pressure (FIP) and fuel injection timing (FIT) on the performance, combustion, and emission characteristics of a hydrogen dual-fuel engine using Madhuca indica biodiesel as the pilot fuel. Experiments were conducted at hydrogen flow rates of 5, 7, and 9 L/min, with injection pressures of 500, 750, and 1000 bar and injection timings of 12° and 18° before top dead centre (bTDC). The results showed a significant improvement in brake thermal efficiency (BTE), increasing from 25.02% for conventional diesel operation to 32.15% under optimized dual-fuel conditions, particularly at 9 L/min hydrogen, 1000 bar FIP, and 18° bTDC FIT. Higher injection pressure and advanced timing also enhanced in-cylinder pressure and heat release rate (HRR). Emission analysis revealed marked reductions in unburned hydrocarbons (59.52%) and soot (46.15%) at 9 L/min hydrogen, 1000 bar FIP, and 12° bTDC FIT, although NOx increased by 20.61% at 18° bTDC due to higher combustion temperatures. Gene Expression Programming (GEP) showed strong predictive capability, supporting future model-based real-time engine optimization for cleaner combustion aligned with SDG 7 and SDG 13.