A laser tomographic investigation of liquid fuel sprays

A light scattering technique is combined with a tomographic transformation to convert line of sight integrated data, measured in sprays, to measurements of droplet size and concentration in volume elements within the spray. The technique is developed and assessed by systematic experiments in axisymmetric sprays generated by twin-fluid atomisers. The angular distribution of forward scattered light from a laser beam passing through the spray is measured for a series of scans with the beam passing through different sections of the spray at the same axial position. This data is transformed numerically into 'point' measurements of droplet size distribution and volume concentration and these measurements are compared with data obtained by analysis of spark photographs obtained in the same spray. The good agreement found shows that, provided certain conditions are satisfied by the local spray structure, the new technique provides information on spray structure, similar in detail and extent to that derived by photography, but with reduced experimental time. The technique is applied to an investigation of a kerosene spray vaporizing in a hot gas stream. Measurements are made of local droplet size distributions and vaporization rates in the spray. Tomographic data analysis increases the useful information which can be derived from light scattering measurements in sprays and the method provides useful data on the detailed physical structures of twin-fluid atomised sprays.