Submicron aerosols of liquid fuels: Method of production, experimental characterization and a semi-empirical model

For combustion processes involving the atomization of liquid fuels, the minimization of droplet size is important for enhancing fuel vaporization, increasing the efficiency of air-fuel mixtures, and reducing soot and NO_x emissions. In this paper, a methodology for producing aerosols of submicron-sized droplets for liquid fuels is presented. The method of droplet formation is based on disintegration, by gas jets, of thin liquid films formed as bubbles on a liquid surface. Using compressed air and CO₂, we atomized and studied droplet aerosols of gasoline, diesel, and 0.1–2 wt% aqueous solutions of sodium alginate, with dynamic viscosities up to 210 mPa s, as models of a highly viscous alternative fuel. The produced droplet volume distributions were bi-modal with two peaks between the droplet diameters 0.1–1 µm and 1–10 µm; the respective volume and Sauter mean droplet diameters were substantially smaller than typically produced by other atomization methods, reaching minima between 0.4 and 0.7 μm. The liquid flow rates of a few hundreds of mg/min for 2 wt% sodium alginate solution and ∼20 g/min for gasoline were measured. The minima of the observed air-to-liquid mass ratios were smaller than the respective stoichiometric air-fuel ratios. Dimensional analysis allowed identifying a dimensionless parameter not previously described in the literature, which plays a primary role in the aerosol production process. This analysis and the experimental data enabled establishment of a semi-empirical model describing the droplet aerosol production by the liquid atomization method used here. The potential advantages demonstrated in this study over the existing fuel atomization techniques include the small size of the generated droplets, simplicity of the method and the device design, low-cost of manufacturing, easy operation and scale-up. Submicron fuel droplets are expected to decrease environmental impact in combustion applications, which suggests further investigations and development of the presented fuel atomization technique.