Droplet Combustion Characteristics of Biodiesel–Diesel Blends using High Speed Backlit and Schlieren Imaging

This work investigates the effect of blending biodiesel with diesel on the combustion of an isolated fuel droplet. Biodiesel blends substituting diesel oil in different concentrations on volumetric basis, in addition to neat diesel and biodiesel, were studied. High-speed Schlieren and backlighting imaging techniques have been used to track droplet combustion. The results showed that partial substitution of diesel oil by biodiesel at the test conditions led to increasing secondary atomization from the droplet, compared to neat diesel or biodiesel fuel droplets. This in turn enhances evaporation, mixing, and then combustion. Additionally, the results showed that biodiesel has a higher burning rate compared to diesel, and that increasing biodiesel in the blend increases the burning rate of the blend. Nucleation has also been traced to take place inside the droplets of the blends. Moreover, flame size (height and width) has been reduced by increasing biodiesel concentration in the blend.