A Computational Fluid Dynamics-based Correlation to Predict Droplet Sauter Mean Diameter for Σ− Yliq Atomization Model in Pressure Swirl Atomizer

Liquid atomization is crucial to ensure efficient combustion as it is an inherent part of the injector system. The combustion of fuels relies on effective atomization to increase the surface area of the fuel and consequently achieve high rates of mixing and evaporation. Pressure swirl atomizers are inexpensive and reliable type of atomizer for fuel injection owing to its superior atomization characteristics and relatively simple geometry. The Sauter mean diameter (SMD) of atomizer contributes significantly to the combustion chamber performance. This paper presents a two-step strategy to predict droplet SMD for atomisation model in pressure swirl atomizer through the combination of experimentally validated Computation Fluid Dynamics (CFD) and Optimal Latin Hypercubes (OLHC) Design of Experiments (DoE) techniques. A three-dimensional Eulerian two-phase CFD model is developed to account for liquid and gas phases as a single continuum with high-density variation at large Reynolds and Weber numbers and validated against experimental measurements, before being employed to carry out a parametric study involving operating conditions and fluid properties of the pressure swirl atomizer. The atomizer is then represented in terms of four design variables, namely liquid viscosity, liquid velocity, surface tension and atomizer exit diameter. An 87-point OLHC DoE is constructed within the design variables space using a permutation genetic algorithm resulting in an accurate SMD prediction. Results show the newly developed SMD prediction is found to be superior compared with existing correlations and indicate significant improvement in the droplets SMD.

Characteristics of Spray Angle and Discharge Coefficient of Pressure-Swirl Atomizer

A widely distributed spray is an important feature for an atomizer which is required in various applications such as gas cooling, gas turbine combustion, and fluidized bed granulator. Pressure-swirl atomizer is an example of atomizer which provides a wide spray angle through the swirling effect inside the atomizer. One of the important parameters affecting spray angle is atomizer geometrical constant, K. Another important parameter of pressure-swirl atomizer is discharge coefficient, Cd. Discharge coefficient describes the throughput of the liquid flow. An experimental test-rig was constructed to conduct the performance test of the atomizer. Acquired images were analysed using image-processing software. It was found that K has inverse relation with spray angle and direct relation with Cd. Prediction of spray angle and Cd using existing correlations also yields similar trends with the experimental results, but some parameters still need to be considered to perform an accurate prediction.

Effect of Low Ambient Pressure on Spray Cone Angle of Pressure Swirl Atomizer

Pressure swirl atomizers are widely used in gas turbine combustor; this paper is aimed at researching the effect of low ambient pressure (0.1 MPa to 0.01 MPa, lower than an atmosphere) on the spray cone angle of pressure swirl atomizer. The spray angle is captured by high-speed photography; then, an image post program is used to process the spray angle magnitude. A mathematical model of a single droplet’s movement and trajectory based on force analysis is proposed to validate the spray angle variation. The maximum variation of the spray cone angle, which is observed when fuel supply pressure drop through the atomizer is 1 MPa as the ambient pressure decreases from 0.1 MPa to 0.01 MPa, is found to be 23.9%. The experimental results show that the spray cone angle is expected to increase with the ambient pressure decrease; meanwhile, mathematical results agree well with this trend.