Study on hybrid airblast atomization

Abstract

To provide a better understanding of the performance of the hybrid atomizer, where the atom ization process is accomplished under the combined effects of liquid pressure and airblast, an investigation has been conducted. Several fuel-injector configurations were selected in such a way to enable the evaluation of the actual role played by the air/liquid relative velocity and other key factors in the atomization process. A number of pressure swirl liquid atomizers that varied significantly in flow capacity, and several air nozzles of different flow areas, were employed in the tests. A calculation approach was formulated to ensure that more realistic liquid and air velocities at the exit of the atomizer were estimated. The spray measurements were performed using a Malvern particle analyzer. The results indicated that the utilization of the airblast effect in the atomizer was not always beneficial. It was also observed that the liquid pressure associated with minimum relative velocity did not coincide with the value that resulted in the least efficient atomization at a given air pressure drop. It was, thus, concluded that the relative velocity was not the only parameter controlling the spray quality. The separate effect of the air/liquid ratio on atomization was found to be most beneficial under low air pressure drop and over a range of low air/liquid ratios. The relative importance of various parameters was investigated by conducting the test under conditions selected in such a way to maintain the same relative velocity while varying either liquid pressure or air pressure drop. The results demonstrated that better atomization could be achieved under high liquid pressure than that obtained under low liquid pressure for the same level of relative velocity. The effects of both liquid pressure and relative velocity were significantly reduced at a higher air pressure drop.