Combustion characteristics of an agricultural diesel engine fuelled with papaya and stone fruit biodiesel: A comparison

A comparative study of the combustion characteristics of an agricultural diesel engine fuelled with papaya seed oil (PSO) biodiesel and stone fruit kernel oil (SFO) biodiesel along with diesel was performed. A 3.3 L heavy duty tractor diesel engine with four-cylinder 4-stroke, EURO II standard was used for the comparison. Two binary blends of each of the biodiesels were prepared with 10% and 20% by volume, with the remaining volume made up of petro diesel. All fuel samples were tested at 1400 rpm (rated torque) and 2400 rpm (near rated power output) at full engine load condition. The experimental investigations were conducted to evaluate the effects of binary blends on engine combustion characteristics such as in-cylinder pressure, heat release rate, ignition delay, mass fraction burned, and ignition duration. The results show that all PSO biodiesel blends had higher in-cylinder pressure; for instance, PSO20 had 2.4% and 1.4% higher peak pressure compared to diesel and SFO20. Heat release rate (HRR) values of both PSO and SFO biodiesel blends were found lower than diesel due to shorter ignition delay and lower calorific values of the biodiesel. The maximum HRRs at 2400 rpm of PSO10, PSO20, SFO10, and SFO20 were found to be 4.1%, 5.4%, 11.1%, and 11.8% lower than that of diesel. PSO and SFO blends were found to have lower ignition delay period compared with the diesel. Again, both biodiesel blends show faster combustion than diesel. However, SFO20 showed 7.1% and 6.5% slower than PSO20 at 1400 rpm and 2400 rpm respectively. Overall, PSO blends performed better than SFO blends in all combustions.