EXPERIMENTAL STUDY ON MICROSCOPIC CHARACTERISTICS OF IMPINGING SPRAY AT ELEVATED AMBIENT PRESSURE CONDITIONS DURING DEVELOPMENT

In this study, spray impingement on the wet wall under different ambient pressure from 0.1 to 1.0 MPa was characterized along development. Particle image analysis (PIA) technology was used to capture the microscopic phenomena. The diameter and velocity for the impinging droplets were analyzed and compared. For a single drop, the occurrence of splashing behavior can be easily determined from the clear visualization. However, for the multiple droplets, the fuel film mass should be introduced for evaluation as the splashing droplets decrease the liquid film on the wall. Dimensionless parameters including Weber number (We), Reynolds number (Re), Ohnesorge number (Oh) as well as K were employed to match the splashing threshold of the droplets. Results showed that microscopic behaviors along spray development could be recorded through PIA method. Droplet velocity is more sensitive to ambient pressure and location than size. Fuel spray development is the process of Weg decreasing with spray breakup and atomization. But Wel can only describe the impinging behaviors for the tendency with poor accuracy to predict. Moreover, under Pamb = 0.1 MPa, the averaged velocity at downstream direction is reversed at (22, 14), indicating most droplets splash off the wall after impingement. However, the reversal direction disappears when the ambient pressure increased to 0.5 and 1.0 MPa, suggesting fewer splashing droplets at elevated ambient pressure. Furthermore, various single drop impacting models are tested and mapped with the impinging spray data, and results suggested that Bai model could match the impinging tendency. However, K number fails to display it, let alone predict the behaviors