Effect of fuel injection timing with waste cooking oil as a fuel in a direct injection diesel engine

For a diesel engine, injection timing is a major parameter that sensitively affects the engine performance, emission and durability. The physical and chemical properties of vegetable oils are known to be different from those of diesel. This study examines the changes in the behaviour of waste cooking oil (WCO) with changes in injection timing of a direct injection (DI) diesel engine, compared with those of diesel. The aspects taken into consideration were the effects of injection timing on combustion, performance and emissions. The results reveal that WCO and diesel responded identically to injection timing changes. To reduce NO, emission, one of the methods is to retard the injection timing from MBT timing. The engine used in this research follows this technique and had its original injection timing set at 15degrees before top dead centre (BTDC). With injection timing advanced by 4degrees, the engine produced better efficiency by 1.6 per cent for WCO and by 1.1 per cent for diesel, reduced CO emission, by averages of 9.9 per cent for WCO and 44.9 per cent for diesel, but suffered increased NO emission of 76.6 per cent for WCO and 91.4 per cent for diesel. In all instances, WCO had shorter ignition delays than diesel, but the ignition delay for WCO was more sensitive to load and injection timing than that for diesel. The test engine could run on WCO with the original injection timing, and altering the timing could result in a trade-off between performance and emission.