Performance and emission characteristics of CNG-fueled compression ignition engine with Ricinus communis methyl ester as pilot fuel

Surge in petroleum prices, its drying sources and degradation in air quality focused interest on renewable energy sources as substitute for existing fuels for internal combustion engines. This study highlights the combustion, performance, and emission characteristics of diesel engines fueled with compressed natural gas (CNG) as primary fuel and castor (Ricinus communis) oil methyl ester (COME) as pilot fuel. COME was produced from non-edible grade Ricinus communis oil. The biodiesel fuel properties and characterization was done as per ASTM D6751 specifications. The CNG was inducted through inlet manifold fumigation at a consistent flow rate of 15 l/min under dual-fuel mode. It is evident from the test results that B20-CNG yields brake thermal efficiency of 23.6% when compared to 25 and 27% for D-CNG and diesel fuel, respectively. The peak cylinder gas pressure was lower in dual-fuel mode when compared to conventional diesel. The emission results show increase in NO_x emission by 24.5 and 28.4% for D-CNG and B20-CNG, respectively when compared to baseline diesel fuel at full engine load. There was increase in HC emission by 6.7 and 11% whereas CO emissions decreased by 31.6 and 37.4% for B20-CNG and D-CNG, respectively at similar operating conditions. Reduction in smoke opacity by 49.4 and 59.6% was achieved respectively for D-CNG and B20-CNG under dual-fuel mode. On the whole, COME exhibits a better pilot fuel choice for dual-fuel combustion mode in comparison to conventional fossil petroleum diesel in terms of combustion, performance, and emissions characteristics.