Abstract

The combustion and emission characteristics of vegetable oils and derivatives are quite different from mineral diesel due to their relatively high viscosity, density, and vaporisation characteristics. These properties affect the fuel spray and the interaction of the spray with air in the combustion chamber therefore it is important to analyse the spray characteristics e. g. spray tip penetration, spray cone angle, spray area, and fuel atomization. Optical techniques for spray visualization and image processing are very efficient to analyse the comparative spray parameters for these fuels. Present research investigates the effect of chamber pressure on spray characteristics of jatropha straight vegetable oils (J100) – blends (J5, J20), and jatropha biodiesel (JB100) – blends (JB5, JB20) vis-à-vis baseline data of mineral diesel. Experiments were performed for all these fuels/ blends injected in a constant volume spray visualisation chamber (cold chamber) at four different chamber pressure (1, 4, 7, and 9 bar, respectively). It was found that J100 and JB100 have the highest spray tip penetration, cone angle, and the spray area followed by J20, J5, mineral diesel and JB20, JB5, mineral diesel, respectively, however J20, J5 and JB20, JB5 have better atomization characteristics as compared to J100 and JB100, respectively. Cone angle was higher for biodiesel blends as compared to straight vegetable oils blends at atmospheric pressure however as the chamber pressure was increased to 9 bar, it became almost equal for both fuel types. Spray parameters are found to be excellent for mineral diesel followed by jatropha biodiesel and jatropha oil. It was found that atomization of fuel becomes superior with increasing chamber pressure.