Effect of Injection Parameters on the Combustion and Emission Characteristics in a Compression Ignition Engine Fuelled with Waste Cooking Oil Biodiesel

An experimental study was conducted to investigate the impact of injection parameters on the combustion and emission characteristics in a compression ignition engine fuelled with neat waste cooking oil (WCO) biodiesel. A single-cylinder diesel engine equipped with common-rail system was used in this research. The test was performed over two engine loads at an engine speed of 800 r/min. Injection timing was varied from −25 to 0 crank angle degree (CAD) after top dead center (aTDC) at two different injection pressures (80 and 160 MPa). Based on in-cylinder pressure, heat release rate was calculated to analyze the combustion characteristics. Carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NO_x) and smoke were measured to examine the emission characteristics.

The results showed that the indicated specific fuel consumption (ISFC) of WCO biodiesel was higher than that of diesel. The ISFC was increased as the injection timing was advanced and injection pressure was increased. The start of combustion of WCO biodiesel was later and the peak heat release rate was lower than diesel due to poor evaporation and atomization characteristics of WCO even though its cetane number (CN) is slightly higher. In terms of emission, WCO had benefits in reduction of CO, HC and smoke under most experimental conditions especially with high injection pressure. The NO_x emissions were higher than those of diesel under most experimental conditions. However, the increase of NO_x emissions with WCO was not significant under high pressure injection condition.