Comparative Experimental Evaluation of Diesel and Dual-Fuel (Diesel-Natural Gas) Engine Performance, Combustion, and Emissions

Compressed natural gas (CNG) as a primary fuel in diesel dual-fuel (DDF) engines can substantially reduce exhaust emissions without insignificant engine modification. A single-cylinder, constant-speed (1500 rpm) compression ignition engine was tested at 25%, 50%, 75%, and 100% engine load. CNG was port-injected through four durations 7, 10, 12, and 14 µs strategy. CNG energy contribution ranged from 52% (DNG7) to 86% (DNG14) at no-load, falling to 24–71% at full load as pilot diesel demand increases. The lower quantity of pilot diesel led to later ignition, lower cylinder peak pressures and decreased heat release rates in comparison to pure diesel for partial loads. At full load, DNG10 attained a peak cylinder pressure of 48.33 bar against 49.17 bar for base diesel. Brake thermal efficiency climbed to 34.56% (DNG14) from 26.68% (diesel baseline) at rated output. NOx dropped from 1407 ppm (diesel) to 523 ppm (DNG14) at full load while CO₂ reduced by up to 33.9%. CO and HC penalties at light loads diminished progressively with rising load as combustion temperatures improved oxidation. DNG10 provided the most efficient, stable, and pollutant reducing performance throughout the range of load.