Experimental analysis of ethanol-biodiesel-CuO nanofuel blends in a modern diesel engine under varying EGR and speed conditions

This study examines the combined influence of waste cooking oil-derived second-generation biodiesel (B20), ethanol (5% and 10% v/v), and CuO nanoparticles (50 and 75 ppm) on the combustion, performance, and emission characteristics of a BS VI-compliant diesel engine at 50% load, 500 bar injection pressure, and 23°bTDC injection timing, with EGR ranging from 0% to 30% across speeds of 1500–2500 rpm. All fuel formulations satisfied ASTM specifications, and UV–Visible spectroscopy confirmed nanoparticle suspension stability over 20 days, with absorbance losses below 11%, the smallest decline of 10.9% recorded for B20 + E10 + 75 ppm NPs. The optimum blend, B20 + E10 + 75 ppm NPs, delivered a maximum cylinder pressure of 72.02 bar at 2500 rpm, 15.3% above diesel (62.48 bar), alongside peak net heat release rate of 65.21 J/°CA (10.1% gain) and cumulative heat release rate of 0.749 (16.1% gain), confirming substantial improvement in in-cylinder energy conversion. Brake thermal efficiency reached a maximum of 27.1% at 2500 rpm, 6.3% above diesel, while brake specific fuel consumption attained a minimum of 0.260 kg/kWh, 5.8% below diesel. Under 30% EGR, the optimum blend exhibited a moderate BTE reduction of 4.6%, considerably lower than the 9.0% recorded for diesel, demonstrating greater thermal resilience under diluted intake conditions. Emission measurements showed maximum CO and UHC reductions of 29.7% and 46.7% at 2500 rpm relative to diesel under 0% EGR. NO x peaked at 60 ppm for B20 + E5 + 50 ppm NPs but was reduced to 43 ppm with B20 + E10 + 75 ppm NPs, approaching the diesel baseline of 42 ppm. EGR at 30% further suppressed NO x to 24–31 ppm across all speeds, representing a 42–57% reduction. Three-way ANOVA confirmed statistically significant effects of all three factors on every response variable (p < 0.05), with R² ≥ 98.9% and coefficient of variation below 2%, validating experimental reliability. B20 + E10 + 75 ppm NPs at 2500 rpm and 20% EGR constitutes the most viable sustainable fuel strategy for next-generation compression ignition engines.