Characterisation of charged hydrocarbon sprays for application in combustion systems

Phase Doppler anemometry measurements and flow visualizations are used to measure the structures of electrostatically atomized hydrocarbon fuel sprays, produced by charge injection nozzles. Due to the jet and drop breakup mechanisms that occur for electrostatically charged insulating liquids, these sprays contain relatively large numbers of small drops which are repelled away from the spray core region where the radial electric field component is high. The largest drops remain near the spray centreline and a radial stratification of the average diameter occurs, which can be advantageous for flame stabilisation. Droplet size reduces with increasing specific charge for the spray. Higher values of specific charge are obtained for reduction of orifice diameter, optimum positioning of the nozzle electrode, and increasing liquid flow rate. On the basis of the measurements, descriptions are given of the physics of processes both inside the atomizer and in the spray and the importance of operating the atomizing nozzle at electrohydrodynamically supercritical conditions is described.