Characteristics of Diesel Spray Flame under Flat Wall Impinging Condition - LAS, OH∗ Chemiluminescence and Two Color Pyrometry Results

The effect of spray/wall interaction on diesel spray flame characteristics was investigated by applying LAS (Laser Absorption-Scattering) technique, OH∗ chemiluminescence and two color pyrometry in a constant volume vessel. To insure the precision of this investigation, following necessary verification experiments were carried out: (1) OH∗ chemiluminescence and two color pyrometry were synchronously employed to analyze the influence of soot incandescence on OH∗ chemiluminescence signal intensity; and (2) frontal view and side view OH∗ images of a linearly arranged three holes injector were concentrated on to investigate the effect of soot on optical intensity attenuation under line-of-sight image recording condition. And then the effect of impinging distance (30,40,50,60 mm and free) on diesel spray and combustion behaviors were studied. The results reveal that the impinging distance plays a significant role in mixture formation. Under severe liquid/wall interaction conditions (30 and 40 mm impinging distance), the evaporation velocity of the injected fuel is much slower than that of longer impinging distance sprays, and the complete evaporation of spray is observed firstly under 60 mm impinging distance condition. When it comes to the combustion experiment, it proves that the possible contribution to OH∗ chemiluminescence signal from soot incandescence is negligible and the effect of soot on optical attenuation is also not significant when applying the line-of-sight technique under the conditions of the current study. The results also show that reactive intensity is improved by increasing impinging distance. Under 60 mm impinging distance, the reactive rate at initial combustion stage is faster than that of free spray flame without damaging maximum integrated OH∗ intensity.