Comparison on the effect of using diesel fuel and waste cooking oil biodiesel as pilot fuels on the combustion, performance and emissions of a LPG-fumigated compression-ignition engine

The present investigation was conducted on a 4-cylinder diesel engine fueled with either pilot diesel, or pilot waste cooking oil biodiesel (WCOB), and fumigated liquified petroleum gas (LPG) at three loads. The LPG addition is expressed in terms of a LPG power substitution percentage (LPSP), ranging from 10 to 30% at each load. This investigation aimed at comparing the combustion, performance and emissions characteristics between the two types of dual-fuel operation, one using pilot diesel and the other using pilot WCOB, with emphasize on the particulate mass and number concentrations. The results show that the combustion characteristics, involving heat release rate, peak cylinder pressure, start of combustion, combustion duration and CA50 of the LPG-fumigated engine, are modestly influenced by the type of pilot fuel in use. The impacts of the LPSP on the brake specific fuel consumption and brake thermal efficiency are negative at low load and positive at high load, for both types of pilot fuel. Regarding the emissions, it can be concluded that both types of dual-fuel operation can lead to reduction in both NO_x and PM emissions, with LPG-Diesel operation being more effect in reducing NO_x emissions while LPG-WCOB operation more effective in reducing particulate emissions.