Effects of size factors and velocity of impinging diesel spray flames on wall heat transfer

Abstract

To examine the effects of size and velocity of impinging diesel spray flames on wall heat transfer, this study conducted visualization of the spray flame and measurements of wall heat flux in a constant volume vessel. The impinging flame velocity was varied by adjusting the injection velocity. To vary the flame size independently of the flame velocity, the nozzle orifice diameter and the nozzle-to-wall distance were varied under similarity conditions, while maintaining a constant ratio of nozzle-to-wall distance to orifice diameter. Care was taken to minimize wall interference from the liquid phase and unburned regions of the spray flame by employing a high cetane number fuel and increasing the nozzle-to-wall distance. The experimental results showed that the wall heat flux increased as the impinging velocity increased, and the flame width decreased. The power-law correlations between the Nusselt and Reynolds numbers were determined based on the experimental results, revealing that the exponent of the Reynolds number reaches a local minimum at the impingement point. As the radial displacement from the impingement point increases, the exponent of the Reynolds number approaches approximately 0.8, which is a typical value for turbulent wall flow.