Assessment of soot particle-size imaging with LII at Diesel engine conditions
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Two-time-step laser-induced incandescence (LII) imaging was performed in Diesel engine-relevant combustion to investigate its applicability for spatially resolved measurements of soot primary particle sizes. The method is based on evaluating gated LII signals acquired with two cameras consecutively after the laser pulse and using LII modeling to deduce the particle size from the ratio of local signals. Based on a theoretical analysis, optimized detection times and durations were chosen to minimize measurement uncertainties. Experiments were conducted in a high-temperature high-pressure constant-volume pre-combustion vessel under the Engine Combustion Network’s “Spray A” conditions at 61–68 bar with additional parametric variations in injection pressure, gas temperature, and composition. The LII measurements were supported by pyrometric imaging measurements of particle heat-up temperatures. The results were compared to particle-size and size-dispersion measurements from transmission electron microscopy of soot thermophoretically sampled at multiple axial distances from the injector. The discrepancies between the two measurement techniques are discussed to analyze uncertainties and related error sources of the two diagnostics. It is found that in such environment where particles are small and pressure is high, LII signal decay times are such that LII with standard nanosecond laser and detector equipment suffers from a strong bias toward large particles.
KeywordsLaser Fluence Soot Particle Soot Volume Fraction Diesel Spray Soot Temperature
The authors thank Clement Bramoulle at IFPEN for experimental assistance. The authors are grateful to Hideyuki Yoshimura of Department of Physics, Meiji University, for providing the TEM. The authors also thank Kei Okabe, Kota Suzuki, Hiroyuki Takano, Junya Takahashi, and Yuki Hattori for their assistance in TEM analysis. Thomas Dreier and Christof Schulz acknowledge support from the German Science Foundation, DFG, through SCHU1369/3.
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