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.
