Cenker, E., Bruneaux, G., Pickett, L., and Schulz, C., "Study of Soot Formation and Oxidation in the Engine Combustion Network (ECN), Spray A: Effects of Ambient Temperature and Oxygen Concentration," SAE Int. J. Engines 6(1):352-365, 2013, doi:10.4271/2013-01-0901.
Within the Engine Combustion Network (ECN) spray combustion research frame, simultaneous line-of-sight laser extinction measurements and laser-induced incandescence (LII) imaging were performed to derive the soot volume fraction (fv). Experiments are conducted at engine-relevant high-temperature and high-pressure conditions in a constant-volume pre-combustion type vessel. The target condition, called "Spray A," uses well-defined ambient (900 K, 60 bar, 22.8 kg/m₃, 15% oxygen) and injector conditions (common rail, 1500 bar, KS1.5/86 nozzle, 0.090 mm orifice diameter, n-dodecane, 363 K).Extinction measurements are used to calibrate LII images for quantitative soot distribution measurements at cross sections intersecting the spray axis. LII images are taken after the start of injection where quasi-stationary combustion is already established. In addition, by changing the LII timing relative to the injection, the temporal variation of the soot cloud is ob-served from initial soot formation until soot oxidization. OH-chemiluminescence imaging was used to determine the lift-off length, relative to the soot-forming region and used to interpret the soot measurements.Results show that Spray A is a moderately sooting flame where signal trapping is not significant, aiding the potential for quantitative soot diagnostics. Maximum soot volume fractions around 2-3 ppm are obtained at the nominal ambient temperature defined for Spray A (i.e., 900 K) that rise to 12 ppm at elevated temperature (1030 K). At 1.5 ms nominal injection duration the Spray A soot cloud is mainly transient. Therefore, an extended injection duration of 4 ms at identical rail pressure was used to characterize the soot structure in quasi-steady mode. Variations of ambient temperature and oxygen concentration are carried out showing effects on soot formation and oxidation that are consistent with the literature.