Two-color laser-induced incandescence (2C-LII) technique for absolute soot volume fraction measurements in flames

Abstract

A two-color version of the laser-induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in flames. By using a calibrated tungsten ribbon lamp, soot peak temperatures were measured as a function of fluence at several locations in an ethylene diffusion flame by using a steeply edged laser beam profile. Above a certain fluence threshold, peak temperatures were tightly distributed just above 4000 K independent of the particle size and number density. Radial profiles of soot volume fraction were obtained and compared (not calibrated) with results from the laser extinction technique. Good agreement showed the validity of the 2C-LII technique at a controlled fluence.

Analysis of uncertainties in instantaneous soot volume fraction measurements using two-dimensional, auto-compensating, laser-induced incandescence (2D-AC-LII)

“…In [47] soot volume fraction results were plotted for a range of possible E(m) slopes and it was found that soot volume fraction varied from −30% to 65% as the slope of E(m) was varied over a realistic range. De Iullis et al [24] noted the influence of E(m) λ in their data interpretation and inconsistencies between optimal choice for E(m) λ in LII and extinction measurements and suggested the need for a follow up investigation. Liu et al [42] presented a formalized analysis of the sensitivity of soot temperature and concentration from auto-compensating LII and noted a strong dependence of soot volume fraction on E(m) 1 and E(m) 2 .…”

“…The second strategy involves measurement of the temperature of the heated soot in real-time by two-color emission pyrometry [9,[23][24][25]. Since the temperature of the soot is explicitly calculated based on measurements, it is not necessary to reach sublimation temperatures, and thus the diagnostic is less intrusive and less sensitive to in-flame laser attenuation [23].…”

Sequential signal detection for high dynamic range time-resolved laser-induced incandescence

“…Twocolor (2C) pyrometry is frequently used for detecting the particle temperature by measuring the ratio of LII signals in two wavelength bands [2][3][4][5][6]. The signal-to-noise ratio (SNR) of LII measurements strongly decreases with signal duration because of the exponential decay of the signal intensity following the initial heat-up of the gas-borne particles with a pulsed laser.…”

Experimental and theoretical comparison of spatially resolved laser-induced incandescence (LII) signals of soot in backward and right-angle configuration

“…The sensitivity of this technique can be further enhanced by using a cavity ringdown setup [14,15]. Another solution for calibration is to use a two-colour LII approach in combination with a calibration lamp [16,17].…”