Experimental study on flat-wall impinging spray flame and its heat flux on wall under diesel engine–like condition: First report—effect of impingement distance

Abstract

Reducing heat loss is one of the most important development concerns for improving the thermal efficiency of the diesel engine. In order to know heat transfer through the combustion chamber wall more clearly, the effects of flame impingement on transient heat flux to the wall were investigated. Using a high-pressure and high-temperature chamber under diesel engine–like conditions, fuel was injected from a single-hole injector against an impingement wall. Surface heat flux of the impingement wall was measured by temperature with three thin film thermocouple heat flux sensors. Simultaneously, luminous flame, flame temperature, and soot distribution were also investigated. The results showed that temperature near the wall and flame contact area have great influence on the local heat flux. Furthermore, local heat flux, combustion, and soot formation reached maximum levels at some spray impingement distance to the wall.

Effects of injection pressure and impingement distance on flat-wall impinging spray flame and its heat flux under diesel engine-like condition

“…After validating, we were able to use the data for calculation. We explained in the previous report 8 that the local heat flux increase came from convection by turbulent spray arrival in both combustion and non-combustion cases. Convection is dominant for the wall heat transfer by impinging spray flame.…”

“…The experiment was carried out same as of previously conducted by Mahmud et al 8,9 using high-pressure and high-temperature chamber vessel, which can be seen in Figure 1. It had four side windows.…”

“…The equation employed for instantaneous local heat flux, total heat loss, and affected areas can be found in our previous report. 8…”

“…To obtain the instantaneous local heat flux on the wall surface, three Alumel/Chromel Thin Film Thermocouple Heat Flux Sensors (TFTHFSs) (Medtherm 10702B) were applied as shown in Figure 1 instantaneous local heat flux, total heat loss, and affected areas can be found in our previous report. 8 Furthermore, so as to predict heat transfer coefficient (a) by CFD (computational fluid dynamics) precisely, we need accurate a experimentally. Steady state heat transfer coefficient is expressed in equation 4, but this relation is also applicable for the transient heat transfer…”

“…where Nu, Re, and Pr are defined as the following equations (6)- (8). m and n are defined based on the laminar or turbulent heat transfer.…”