Diffuse Back-illuminated Imaging of Soot in an Optical Reciprocating Rapid Compression Machine

An optical reciprocating rapid compression machine has newly been built at NTNU. This study presents high speed 2D diffuse back-illuminated measurements of soot under three different operating conditions. The instantaneous measurements were performed at 40.000 fps with a resolution of 384x160. The study also discusses different issues connected to 2D light extinction in high density and high temperature conditions such as beam steering. The effect of beam steering on the measured transmittance was effectively suppressed in the center of the combustion chamber, while observed in the periphery. The effect of flame luminosity on the KL maps are also discussed. The results show that a decrease of injection pressure results in a higher level of soot in the flame, while decreasing the ambient air temperature decreases the soot level.