Investigation of the Effects of Heat Transfer and Thermophysical Properties on Dynamics of Droplet-Wall Interaction

Fuel spray-wall interaction frequently occurs on intake manifold wall in the port fuel injection engine and on the piston in the direct injection engine, especially during the cold start. The heat transfer between the spray and wall is involved in this interaction process and influences the dynamics of the impinged spray which can further affect the engine performance. The physics of impact dynamics of a single droplet serves as a fundamental for better comprehension of spray impingement. In our previous studies, we have focused on diesel droplets, at ambient temperature, impinging on both heated and non-heated wall and found impinged droplet morphology differences. To understand the effect of heat transfer and thermophysical properties on dynamics of droplet-wall interaction better, droplet temperature variation was introduced in this study. Therefore, different conditions were framed to explore the impact of thermophysical properties of the droplet. These conditions were grouped into two: 1) Isothermal: cold wall-cold droplet and heated wall-heated droplet; 2) Non-Isothermal: cold wall-heated droplet and heated wall-cold droplet. Droplet and wall temperature were varied from 25 to 150°C. The impact velocity of the impinging droplet was 1.43 m/s. A high-speed camera and a heat flux sensor were utilized to record morphology changes of the impinging droplet and the heat flux between droplet and wall, respectively. Significant differences in the spatial-temporal evolution of impinged droplet were observed among the mentioned four conditions. The morphology changes in the impinged droplet were quantified using parameters: spreading factor, contact angle and height ratio.