Hydrogen-assisted combustion of GQD-DEE-enhanced WCO biodiesel in a dual-fuel CI engine

The relatively low performance and elevated nitrogen oxide (NOx) emissions associated with biodiesel-fueled compression ignition (CI) engines continue to limit their widespread application. To address these challenges, the present study investigates the combined influence of diethyl ether (DEE), graphene quantum dots (GQDs), and hydrogen enrichment on the performance, combustion, and emission characteristics of a dual-fuel CI engine. Waste cooking oil (WCO)-derived biodiesel was blended with diesel at a ratio of 20:80 (B20) and supplemented with 10 vol.% DEE to formulate a ternary fuel (TF) blend. GQDs were dispersed into the TF blend at a concentration of 50 mg/L using an ultrasonicator (Hielscher UP400S, 160 W, 40 kHz) to ensure stable and uniform dispersion. The physicochemical characteristics of the synthesized GQDs were analyzed using Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and High-Resolution Transmission Electron Microscopy (HRTEM). Hydrogen (H2) was introduced through the intake manifold at flow rates of 5 and 10 LPM, serving as a supplementary fuel. The results demonstrated that the TF + GQD50 + 10H₂ combination yielded the best overall performance. Compared with the baseline fuel, brake thermal efficiency increased by 13.7%, while brake specific fuel consumption decreased by 20.46%. Furthermore, Cylinder Pressure (CP) and Heat Release Rate (HRR) improved by 29.47% and 4.49%, respectively. Significant reductions in Carbon monoxide (CO), Hydrocarbons (HC), NOx, and smoke emissions of 17.52%, 11.01%, 3.90%, and 2.22% were also observed at higher brake power. These findings indicate that the combined use of DEE, GQDs, and hydrogen can effectively enhance biodiesel combustion and emission characteristics, although long-term durability and practical implementation require further investigation.