Spray and Combustion Characteristics of Diesel–Ethanol–Waste Cooking Oil Blends in a Constant‐Volume Combustion Chamber

Diesel–ethanol–waste cooking oil (WCO) blends are considered promising alternative fuels due to their renewability and potential for reduced emissions. This study investigates the spray and combustion characteristics of diesel and diesel–ethanol–WCO blends in a constant‐volume combustion chamber (CVCC). Blended fuels consisting of diesel, ethanol, and WCO with volumetric ratios of 90%–5%–5% (D90E5WCO5), 85%–10%–5% (D85E10WCO5), and 80%–15%–5% (D80E15WCO5), respectively, were tested. Prior to fuel injection, the chamber was maintained at chamber temperatures of 298 and 800 K under a constant pressure of 40 bar. Fuel injection was performed using a common‐rail system, and a high‐speed camera was employed to characterize spray tip penetration (STP), spray cone angle (SCA), and combustion behavior. The results indicate that at an ambient temperature of 298 K and an injection pressure of 200 bar, neat diesel exhibited the longest STP, whereas the D85E10WCO5 produced the largest SCA. Experiments conducted on the D80E15WCO5 under injection pressures ranging from 180 to 220 bar showed that both STP and SCA increased with increasing injection pressure. Under combustion conditions (800 K, 40 bar, and an injection pressure of 200 bar), neat diesel produced the highest peak pressure, whereas D85E10WCO5 exhibited the highest rate of pressure rise (ROPR) and rate of heat release (ROHR), indicating enhanced combustion performance. Overall, the results demonstrated that an appropriate combination of ethanol and WCO provides a favorable balance between spray atomization and combustion performance, highlighting the potential of diesel–ethanol–WCO blends as renewable alternative fuels for conventional compression‐ignition engines.