Comparison of fuel characteristics of hydrotreated waste cooking oil with its biodiesel and fossil diesel.

Compression ignition engines powered by diesel are the work horses of developing countries like India. However, burning fossil fuel causes a lot of air pollution and the depletion of fuel at an alarming rate. Fuels produced from biomass or wastes can partially substitute fossil diesel to decrease its consumption. One such feedstock is waste cooking oil (WCO) which can be easily converted into fuel for diesel engines. The hydrotreating process stands out among the methods available for converting WCO into fuel, since its properties are almost similar to fossil diesel with little or no oxygen content. In this study, the physico-chemical properties of the hydrotreated waste cooking oil (HVO), biodiesel of waste cooking oil, diesel and blends of HVO and diesel are compared. The blends were prepared by mixing 10%, 20%, 30%, 40% and 50% of HVO on volume basis in diesel. The evaporation rate and ignition probability of the fuel samples were found by using a hot-plate test setup. HVO had higher ignition probability than all the test sample. As the percentage of HVO increased in the test samples, the ignition probability increased. The Sauter mean diameter (SMD) of the samples was also found using Malvern Spraytec. The SMD of HVO was larger than diesel but smaller than biodiesel. The study shows that blends of HVO up to 30% are feasible for present use in diesel engines, as the viscosity (2.54, 2.59 and 2.62cSt) and calorific value (42.41, 42.29, 42.08 MJ/kg) of the three blends (10%, 20% and 30%) is close to diesel (2.51cSt and 42.58 MJ/kg). Also, due to high cetane index, neat HVO or blends having higher HVO content (> 30%) cannot be used in the existing engines as the engine power output may be affected. Therefore, to use these fuels, the engine needs to be modified which is not feasible for existing engines. The FTIR and GC-MS analysis shows that the HVO has low oxygen content and high amount of paraffins, whereas biodiesel of waste cooking oil has high unsaturation and high oxygen content.