Research On Fuel Atomization And Evaporation Of Primary Swirler In A LPP Combustor

The process of atomization and evaporation about fuel injecting directly into crossflow, which is a main atomization method in the primary swirler of a Lean Premixing Prevaporizing(LPP) low emission combustor, is studied by both experiments and numerical simulation. The fuel supply of the primary swirler exceeds 80 percent of the total amount, therefore, the atomization and evaporation characteristics of fuel in the primary swirler is one of the most important factors for the low emission performance of a LPP combustor. The fuel is injected directly between the vanes of swirler, then atomizated and evaporated, and fuel evapor mixes with the air, finally the mixture of air and fuel evapor enters the combustor and forms uniform combustion with a lower temperature which generates fewer pollutants(especially for the NOx).This thesis includes three parts:Firstly, in order to investigate the influence of different inlet conditions both air and fuel, and different atomizer diameters, a High Speed Camera is used to capture the process of fuel atomization. Experimental results show that:(1) Weber number of inlet air determines the pattern of atomization;(2) The size distribution of drops is determined mainly by Weber number, while the fuel-air momentum ratio(q) also has an effect for the size distribution, and the atomizer diameter can affect the primary atomization;(3) The fuel-air momentum ratio(q) affects the fuel penetration trajectory in crossflow.Secondly, in order to study the influence of different inlet conditions on evaporation characteristics of fuel injecting into crossflow, the High-Speed Camera and a Cyclone Separator are applied to measure the fuel evaporation ratio at a cross section of the vane. Experimental results show:(1) The fuel evaporation ratio increases with the increase of fuel-air momentum ratio;(2) The fuel evaporation ratio increases obviously when Weber number increases;(3) There is a sharp increase of the fuel evaporation ratio when the spray distance between the atomizer and cross section increases at the airflow direction;(4) The methods used in this thesis is reliable, and results of different methods agree well with each other.Finally, the FLUENT software is used to simulate the atomization process of fuel injecting into crossflow. In order to obtain the best models, different difference methods are used to simulate the atomization process and the simulation results are compared with experimental results. The spray process of fuel injecting into crossflow with different inlet conditions are simulated seperately. The simulation results show that the model and difference method can be applied to simulate the flow field and atomization characteristics when fuel is injected directly into crossflow.The obtained results of this thesis can be used to accurately predict the atomization characteristics and evaporation in a LPP low emission combustor.