Comparison of imaging techniques for measurement of diesel combustion lift-off length.*

The extent of soot formation in direct injection compression ignition engines has been found to correlate with the charge quality upstream of the corresponding reaction zone. Lift-off length (LOL) is a widely-accepted quantity used to infer the amount of air entrainment into the fuel stream which effects the local equivalence ratio at the onset of ignition. Hence, it serves as an important marker investigating soot emissions in Diesel engines. This work therefore compares two imaging techniques used for determining the LOL of a diesel spray, i.e. Broadband natural luminosity and OH* chemiluminescence to discuss the advantages and challenges of each. To this end, data taken at simulated engine-relevant conditions in an state-of-the-art spray facility at Georgia Tech is used.