Blending jatropha biodiesel (JBD) with Fischer-Tropsch synthetic diesel (FT) results in lower CO, THC, smoke and PM emissions compared to neat FT, according to a study by researchers at the Norwegian University of Science and Technology (NTNU) published in the ACS journal Energy & Fuels.
However, NOx emissions were higher, and the engine thermal efficiency was slightly lower with higher JBD blends.
The authors tested JBD blended with FT fuel in volumetric ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 (B0, B25, B50, B75, and B100). Among the findings:
Compared to petroleum diesel (DF), FT fuel showed similar fuel consumption (BSFC) and thermal efficiency. Compared to FT fuel, higher JBD blends showed higher BSFC and lower thermal efficiency.
CO, smoke, THC, TPM, and NOx emissions were reduced with FT fuel compared to DF. The reductions were due to the higher cetane number, low sulfur, and extremely low aromatic compounds in FT fuel.
Significantly lower emissions including CO, smoke, THC, and TPM were realized with B25, B50, B75, and B100 compared to FT fuel. The reductions of these emissions were mainly due to the oxygen in the blended fuel molecules. Higher cetane number was also an additional reason for lower emissions.However, NOx emissions were increased at higher loads with the JBD blended fuels. Higher ROHR (rate of heat release) at the premixed combustion and higher percentages of unsaturated fatty acids with double bonds in the carbon chain with B25, B50, B75, and B100 were the reasons for higher NOx emissions, according to the authors.
Mass and number distributions of fine particles for FT fuel were measured and found to be lower than those of DF for all particle sizes. When the engine was run with JBD blends, significantly lower particle mass and number emissions of fine particles were observed for the whole particle size distribution compared to FT fuel. The reduction in fine particles with FT fuel was due to the low sulfur and extremely low aromatic compounds in FT fuel. The reduction in fine particles with JBD blends was mainly due to the presence of oxygen.
Considering engine performance and exhaust emissions, B25 was suggested to be an environmentally friendly alternative fuel for diesel engines.
Md. Nurun Nabi and Johan Einar Hustad (2010) Influence of Biodiesel Addition to Fischer-Tropsch Fuel on Diesel Engine Performance and Exhaust Emissions. Energy Fuels, 24 (5), pp 2868–2874 doi: 10.1021/ef901317u