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Abstract. In the present work, an experimental investigation of spray atomization of different liquids has been carried out. An air-assist atomizer operating at low injection pressures valued (4 and 6 bar) has been used to generate sprays of (diesel fuel, 5, 10, and 15% water-emulsified-diesel), respectively. A Photron-SA4 high speed camera has been used for spray imaging at 2000 fps. 20 time intervals (from 5 to 100 ms with 5 ms time difference) are selected for analysis and comparison. Spray macroscopic characteristics (spray penetration, dispersion, cone angle, axial and dispersion velocities) have been extracted by a proposed technique based on image processing using Matlab, where the maximum and minimum (horizontal and vertical) boundaries of the spray are detected, from which the macroscopic spray characteristics are evaluated. The maximum error of this technique is (1.5% for diesel spray) and a little bit higher for its emulsions.

The liquid-phase processes occurring during fuel droplet combustion are important in deciding the behaviour of the overall combustion process, especially, for the multicomponent fuel droplets. Hence, understanding these processes is essential for explaining the combustion of the multicomponent fuel droplet. However, the very fast combustion of the too small fuel droplet makes experimental investigation of these processes uneasily affordable. In the present work, a high speed backlighting and shadowgraph imaging of the multicomponent fuel droplet combustion including liquid-phase dynamics are performed. Two categories of multicomponent fuelsin which diesel is the base fuelare prepared and utilized. The first category is biodiesel/diesel and bioethanol/diesel blends, while the second category is the water-in-diesel and diesel-in-water emulsions. Specific optical setups are developed and used for tracking droplet combustion. The first setup is associated with the backlighting imaging with the resulting magnification of the droplet images being 30 times the real size. The second optical setup is used for shadowgraph imaging, with the resulting magnification being 10 times the real size. Using these setups, spatial and temporal tracking of nucleation, bubble generation, internal circulation, puffing, microexplosion, and secondary atomization during the combustion of isolated multicomponent fuel droplets are performed. Spatial and temporal tracking of the sub-droplets generated by secondary atomization, and their subsequent combustion, in addition to their overall lifetimes have also been performed. Accordingly, a comparison of the burning rate constant between the parent droplet and the resulting sub-droplets is carried out. The rate of droplet secondary atomization is higher than those obtained by relatively low imaging rate. Additionally, it is shown that during a large portion of its entire lifetime, the droplet geometry has been affected by combustion significantly.

Droplet impingement on solid surfaces takes place in a variety of industrial and environmental applications. However, there are still some areas that are not fully comprehended; emulsion droplet impact on a heated surface is one of these areas that require further comprehension. Hence, the present work represents an experimental exploration for spread characteristics of diesel-in-water (DW) emulsion droplet impacting a heated flat plate. Three different emulsions in which water concentration is set to 10%, 20%, and 30% of the overall emulsion content by volume have been tested in addition to the neat diesel. The temperature of the flat plate is varied over the range 20, 40, 60, and 80ºC respectively. Magnified high speed direct imaging and shadowgraphy have been used simultaneously for tracking droplet spread over the heated surface post impact. Droplet spread rate, maximum diameter, rebound height and velocity represent the main evaluated parameters. The results show that the maximum spread diameter is proportional while spread rate is inversely proportional to the increase in plate temperature for all diesel concentrations including the neat diesel. Whereas, droplet rebound height and velocity are found to be more responsive to the variation in diesel concentration than the variation in plate temperature, so they are both minimum in the case of neat diesel and are increasing by the decrease of diesel concentration in the emulsions.

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.