Evaluation of pine oil blending to improve the combustion of high viscous (castor oil) biofuel compared to castor oil biodiesel in a CI engine

In this study, neat castor oil having a high viscosity of 226.2 cSt is taken as a base fuel replacing diesel in a CI engine. To improve the combustion characteristics of NCO, various methods like transesterification, blending with diesel and blending with low viscous biofuel namely pine oil (P) were adopted. Pine oil has viscosity of 1.3 cSt, which is only about 1/3rd compared to diesel fuel. On the contrary, low cetane number of pine oil limits its share ratio (30% by volume) due to engine knocking problems. The merits and demerits of the properties of castor oil and pine oil are mutually balanced causing a NO-smoke tradeoff. For comparison purpose, diesel was blended 30% by volume with NCO. All the tests were done in a single cylinder CI engine with rated power of 5.2kW at 1500rpm. Diesel, neat castor oil (NCO), castor oil methyl ester (COME), NCO70+P30 and NCO70+D30 were tested to assess the comparative performance, emission and combustion characteristics at different load conditions. NO emission for diesel is 8.2g/kWh and for NCO and COME it is 5.2g/kWh and 8.99g/kWh respectively. The smoke opacity is 57% for diesel and it exceeds 100% for NCO at full load whereas it is 69% for COME. NCO70+P30 blend increases NO emission to 7.1g/kWh and reduces smoke opacity to 85% compared to neat castor oil. Very low viscosity and better volatility of pine oil, blending it with NCO improves brake thermal efficiency from 23.73% to 29.07% whereas it is 29.73% and 32.93% for COME and diesel operations respectively. While, COME exhibited better combustion compared to other techniques, considering NO-smoke tradeoff and laborious tranesterification process, NCO70+P30 is considered optimum since the performance, combustion and emission characteristics approach closer to COME operation.