|M.Sc Thesis||Department of Aerospace Engineering|
|Supervisor:||Prof. Levy Yeshayahou|
|Full Thesis text - in Hebrew|
The atomization of liquid fuel, its droplet size distribution, mixing and evaporation - all affect the ignition and combustion processes, combustion stability and efficiency. In small-scale jet engines fuel atomization gain even higher importance due to the constraints that characterize small-scale engines: low ignition energy, small combustor volume and the need for simplicity of the atomizers.
The aim of current study was to perform a comparison between two methods of liquid fuel delivery for small-scale jet engine combustors - using atomizers and using vaporizers. Typically, the properties of the atomizers and the vaporizers are provided for a single atomizer or vaporizer working outside the combustor in laboratory environment, but the present study compared between the performances of the entire combustor of a small-scale jet engine while operating once with fuel atomizers and once with fuel vaporizers. The comparison in the study referred to the operational range and efficiency of the combustor, which were evaluated through experimental measurements.
Relying on current study results, it can be concluded that atomizers are preferable for higher fuel flow rates (and temperatures) and have stable operation over wider fuel supply ranges. The vaporizers are preferable for low fuel supply rates (and temperatures). As for combustion efficiencies, the efficiency values for the atomizers in current study were significantly lower compared to those for the vaporizers. These low efficiencies of the atomizers can be explained by the short residence time, which was insufficient to complete the evaporation of fuel droplets, their mixing and combustion within the limited combustion volume.
Additionally to the main part of the study, the present thesis included an experimental investigation of an air pressure distribution in the near field of a single pressure-swirl, air blast atomizer, working outside the combustor in laboratory environment. The investigation revealed that the air swirl established by the atomizer induces a low pressure region near atomizer outlet, contributing the transition from the so called “onion” stage to high quality atomization. The investigation also revealed that the rotation of the liquid “onion” induces a low inner “onion” air pressure that counteracts the transition to the high quality atomization. It was noticed that this inner low pressure varies with fuel flow rate and at a certain finite fuel flow rate reaches a minimal value.