Comparative evaluation of physical and chemical properties, emission and combustion characteristics of brassica, cardoon and coffee based biodiesels as fuel in a compression-ignition engine

Abstract

This study have been considered the effects of the three type of biodiesel (brassica, cardoon and coffee) on the performance, tailpipe emissions and combustion characteristics of a single cylinder direct injection compression ignition engine operated in four different speeds (1200, 1700, 2200, 2700 rpm) and three different engine loads (15, 30 and 45%). The differences in combustion and performance parameters and exhaust emissions of engine fueled by these fuels have been compared. The free fatty acid profile of the biodiesels has been considered. The properties of the biodiesels according to the ASTM D6751 have been analyzed. Highest degree of unsaturation is achieved for biodiesel produced from brassica (94.64%) compared to biofuels derived from cardoon and coffee, 79.81% and 57.65%, respectively. The high value of the erucic acid (C22:1) in the brassica biodiesel (48.7 wt%) is the reason of higher unsaturation degree than the other biodiesels. The components of the free fatty acid profile of the considered biodiesels mostly include long chain free fatty acids (C18 and higher). The physical properties of the biodiesel fuel is influenced by the fatty acid profile. The CN of the brassica, cardoon and coffee is 56.44, 56.11 and 57.44, respectively. The surface tension of the brassica, cardoon and coffee biodiesel fuel is 42.05, 40.99 and 37.62 mN/m. The oxygen content of the brassica, cardoon and coffee is 13.44, 10.91 and 7.77%, accordingly. Dynamic viscosity of the brassica, cardoon and coffee was 6, 5.7 and 9.5 cSt, respectively. The ignition delay of the brassica, cardoon and coffee biodiesel diesel fuel blends at 15% engine load is 9.52, 11.05, 5.07% and at 30% engine load is 12.88, 13.85, 15.78% lower than diesel fuel on average, respectively. The additional oxygen have decreased the CO and THC emissions. The highest reduction of the THC emission than standard diesel fuel was 41.19%. The maximum BTE (brake thermal efficiency) obtained for different biodiesel diesel blends fuels was lower than that of standard diesel fuel. The CA50 of the biodiesel diesel fuels was lower than diesel fuel due to their lower ignition delay.