Macroscopic and Microscopic Spray Characteristics of Diesel and Karanja Biodiesel Blends

Fuel injection pressure (FIP) is one of the most important factors affecting diesel engine performance and particulate emissions. Higher FIP improves the fuel atomization, which results in lower soot formation due to superior fuel-air mixing. The objective of this spray study was to investigate macroscopic and microscopic spray parameters in FIP range of 500-1500 bar, using a solenoid injector for biodiesel blends (KB20 and KB40) and baseline mineral diesel. For these test fuels, effect of ambient pressure on macroscopic spray characteristics such as spray penetration, spray area and cone angle were investigated in a constant volume spray chamber (CVSC). Microscopic spray characteristics such as velocity distribution of droplets and spray droplet size distribution were measured in the CVSC at atmospheric pressure using Phase Doppler Interferometry (PDI). At higher fuel injection pressure (1500 bar) and 40 bar ambient pressure, biodiesel blends spray evolution was slower than baseline mineral diesel, suggesting its stronger atomization with smaller droplet size distribution and consequently the droplet momentum. The spray cone angle of mineral diesel was wider than biodiesel blends. Droplet size distribution represented by Sauter mean diameter (D₃₂) and arithmetic mean diameter (D₁₀) increased with increasing biodiesel concentration in the test fuel. Overall, these results are useful for explaining and comparing the biodiesel fuelled engine behavior.