A comparison of combustion characteristics of waste cooking oil with diesel as fuel in a direct injection diesel engine

Abstract The use of waste cooking oil (WCO) as an alternative to diesel in engines has advantages from both economic and environmental standpoints. Typical of vegetable oils, WCO has a higher viscosity, leading to a general perception that its use is likely to have an adverse effect on the fuel injection system and consequent combustion process. In the present investigation, tests were carried out to determine engine performance and combustion analysis as well as emissions for both WCO and diesel. It was observed that because of the shorter ignition delay the premixed combustion phase of WCO was less intense than that of diesel. However, because of the corresponding smaller combustion volume, the peak pressures were on average 1.5 bar higher and occurred 1.1°-3.8° earlier than for diesel. This early peaking characteristic requires careful attention to ensure that, while running with WCO, the peak pressure takes place marginally after top dead centre for efficient operation. In terms of emissions of CO, NO and SO2, the level was higher for WCO compared with diesel.