Using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter. These reductions increase as the amount of biodiesel blended into diesel fuel increases. The best emission reductions are seen with B100.
The use of biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in biodiesel enables more complete combustion to CO2) and reduces the sulfate fraction (biodiesel contains less than 15 ppm sulfur), while the soluble, or hydrocarbon, fraction stays the same or increases. Therefore, biodiesel works well with emission control technologies such as diesel oxidation catalysts (which reduce the soluble fraction of diesel particulate but not the solid carbon fraction).
Emissions of nitrogen oxides increase with the concentration of biodiesel in the fuel and the increase is roughly 2% for B20. Some biodiesel produces more nitrogen oxides than others, and some additives have shown promise in reducing the increases. More R&D is needed to resolve this issue.
Biodiesel has physical properties very similar to conventional diesel.
Biodiesel's Physical Characteristics:
Specific gravity 0.87 to 0.89
Kinematic viscosity @ 40°C 3.7 to 5.8
Cetane number 46 to 70
Higher heating value (btu/lb) 16,928 to 17,996
Sulfur, wt% 0.0 to 0.0024
Cloud point °C -11 to 16
Pour point °C -15 to 13
Iodine number 60 to 135
Lower heating value (btu/lb) 15,700 to 16,735
Dept. Of Energy