Effect of quality of waste cooking oil on the properties of biodiesel, engine performance and emissions

The number of research activities to find alternative fuels for Internal Combustion Engines has increased tremendously in recent years, owing to depleting oil reserves and growing climate concerns. In this scenario, biodiesel is one of the few promising alternatives that can potentially replace conventional fuel. When vegetable oil is used for frying food items, it undergoes physiochemical changes. After a while, it is discarded as waste cooking oil (WCO) which can be used in the production of biodiesel. Since WCO is a degraded raw material, it is important to understand its effect on the quality of biodiesel produced in terms of engine performance and engine emission. In current research study, total polar matter (TPM) is considered as a measure of quality for waste cooking oil. Sunflower oil and palm olein were used in this study for comparison since both exhibit different fatty acid compositions. Among the properties considered in this study, the results found that the kinematic viscosity of the biodiesel gets highly affected by total polar matter content of waste cooking oil. Further, the study also identified correlations to predict the kinematic viscosity of biodiesel from total polar matter content of WCOs. The authors found no significant difference in engine performance during engine tests between the biodiesels produced from fresh oils and waste cooking oils. However, biodiesels produced from WCOs emitted slightly higher carbon monoxide than the biodiesel produced from fresh oils. On the contrary, nitric oxide and smoke emissions from biodiesels produced from waste cooking oils and fresh oils were similar. Even though waste cooking oil is a degraded feedstock, the biodiesel produced from it has no adverse effect on engine performance and emissions. Therefore, WCO oil can be considered as a promising feedstock in the sustainable production of biodiesel.