Laser Attenuation Technique for Measurements of Droplets in a Turbulent Fuel-Air Aerosol Mixture

Studies of spray combustion in engines or furnaces are complicated due to the multiplicity of dependent parameters. The flame propagation rate in the two-phase-environment must be analysed in isolation from the complex processes of fuel injection and mixing. Therefore, a fundamental study of droplet cloud combustion is required to investigate the parameters of importance. In a study of turbulent flame combustion of droplet and vapour mixtures a spherical explosion vessel, fuel-air aerosols are generated by expansion of a gaseous mixture using the Wilson cloud chamber principle. With this technique suspended droplets would appear when the temperature of the mixture drops below the saturation value. The size of the droplets increases as the temperature is further reduced. A problem encountered in conducting this experiment is that the time for the onset of droplet formation with respect to the start of expansion is not known. Therefore, it would be difficult, with the absence of such information, to plan the pre-ignition condition of the droplet-vapour mixture. Moreover, in order to compare the experimental results with those from other researches, an estimation of the number of droplets within the explosion vessel is required. In this paper, the application of a laser attenuation technique to determine the onset of nucleation of liquid droplet suspensions within turbulent fuel-air aerosol is presented. The laser attenuation technique is supported by a Class-3A laser that is collimated by a set of optical lens. The amount of laser light that passes through the vessel reduces with the presence of droplets. The relationship between the number of droplets within the aerosol and the laser attenuation is described by the Beer-Lambert law.