Green-synthesized silver nanoparticles from endemic Allium tuncelianum and their effects on combustion and emission characteristics of cottonseed oil-derived B20 fuel in a diesel engine

Silver nanoparticles (AgNPs) were synthesized via a sustainable green route using aqueous extract of the endemic plant Allium tuncelianum (Tunceli garlic) and evaluated as an additive in a cottonseed oil-derived B20 biodiesel blend. UV–Vis, FTIR, XRD, TEM, and TGA analyses confirmed the nanoscale morphology, bio-organic surface capping, and thermal stability of the AgNPs. Nanofuels containing 50, 75, and 100 mg/L AgNPs were tested in a single-cylinder, four-stroke, direct-injection diesel engine under steady-state conditions. Combustion behavior was evaluated using heat release rate (HRR), mass fraction burned, pressure rise rate, maximum gas temperature (MGT), combustion phasing, and exhaust emissions. AgNP addition enhanced early combustion kinetics without significantly changing CA50. At the optimal dosage of 75 mg/L, peak cylinder pressure, HRR, and MGT increased by approximately 2.1%, 10.9%, and 1.5%, respectively. Ignition delay and combustion duration were shortened, improving combustion completeness and reducing HC and CO emissions, whereas NOx and CO2 increased because of higher in-cylinder temperatures. At 100 mg/L, the catalytic effect weakened, likely due to nanoparticle agglomeration. Overall, 75 mg/L provided the most balanced combustion and emission performance.