Performance and Emission Analysis of Rubber Seed Methyl Ester and Antioxidant in a Multicylinder Diesel Engine

In this study, the potential of using a nonedible biodiesel source (rubber seed oil) was explored. Rubber seed oil (RSO) is a promising nonedible source for producing a sustainable biodiesel in Malaysia. However, due to the lower oxidation stability of the produced biodiesel, which is the result of its higher unsaturation content (78.73%), an oxidation inhibitor is required. This paper examines the effect of antioxidants addition to rubber seed biodiesel (RB) on the combustion, engine performance, and emissions. Four antioxidants, namely, N,N′-diphenyl-1,4-phenylenediamine (DPPD), 2-tert-butylbenzene-1,4- diol (TBHQ), N-phenyl-1,4-phenylenediamine (NPPD), and 2(3)-tert-butyl-4-methoxyphenol (BHA), were added at concentrations of 1000 and 2000 ppm to 20% RB (RB20). The results showed that TBHQ had the greatest ability to increase the stability of RB20 followed by BHA, DPPD, and NPPD, respectively, without a significant effect on physical properties. The experiments were conducted in a 55 kW multicylinder diesel engine at full load conditions. The results showed that RB20 produced a lower brake power (BP) of 3.07%, higher brake specific fuel consumption (BSFC) of 3.68%, and higher maximum in-cylinder pressure of 6.7% compared to neat diesel. Antioxidants addition reduced the NO, heat release rate (HRR), and maximum in cylinder pressure by an average of 0.85− 4.12%, 5.78−14.74%, and 1.77−3.97%, respectively, compared to RB20. All antioxidant fuels showed a similar start of combustion (−12 °CA BTDC), but for diesel and RB20 the values were −10 and −13 °CA BTDC, respectively. However, carbon monoxide (CO) and hydrocarbon (HC) emissions increased by 10.17− 15.25% and 13.35−19.68%, respectively, compared to RB20. It can be concluded that the RB20 blend treated with antioxidants can be used in diesel engines without any further modifications.