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This manuscript presents the impact of addition of antioxidant additives to rice bran biodiesel blend on the performance and emission characteristics of compression ignition (C.I) engine. Rice bran methyl ester (RBME) was produced from rice bran oil by transesterification using sodium hydroxide as catalyst. An experimental investigation was conducted on a single-cylinder four-stroke C.I engine to analyze the performance and emission characteristics of rice bran methyl ester (RBME) blended with diesel at 20% by volume (B20) with and without addition of 1000 ppm of two monophenolic antioxidant additives, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). The results showed that the BHA- and BHT-treated B20 blend decreased the brake specific fuel consumption (BSFC) by 2.1 and 1.2% and increased the brake thermal efficiency (BTE) by 1.04 and 0.5% compared to B20. The BHA- and BHT-treated B20 blend produced mean reductions in NOx emission of 12.2 and 9.6%, respectively, compared to B20. The carbon monoxide (CO) and hydrocarbon (HC) emissions of BHA- and BHT-treated B20 were increased by 14.8-16.6% and 10.6-11.2%, respectively, compared to B20. However the emission levels were lower than those of diesel.

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This experimental work emphases on the impact of various combustion chamber geometries in a DI engine fuelled with diesel-biodiesel-ethanol blends mixed with alumina nano-additives, named as Highly-Performing Fuel (HPF). The HPF is subjected to various combustion bowl geometries like standard hemispherical chamber geometry (SG), shallow depth re-entrant bowl geometry (CG1), toroidal re-entrant chamber geometry (CG2) and toroidal chamber geometry (CG3). It is observed that, in comparison to SG-HPF, the performance of CG2-HPF was increased with 11.51% higher BTE and 10.37% lowered. Emission-wise, CG2-HPF ensued in lowered CO, HC and smoke emissions by 33.53%, 18.35% and 14.37% respectively in comparison with SG-HPF. Combustion-wise, CG2-HPF ensued in high heat release rate owing to the re-entrant chamber profile of CG2 which improves mixing rate of air-fuel mixture, atomization, evaporation rate ensued by better efficient combustion, increased cylinder pressure and HRR rate. The re-entrant profile geometry helps to sustain the fuel mixture’s turbulent kinetic energy and re-channels them towards the combustion zone. This tends to lower the stagnation of rich mixtures inside the combustion zone. Overall, CG2 geometry is found to be the optimum geometry profile for HPF in lieu of improved performance and combustion characteristics along with lowered exhaust emissions.