Two-dimensional soot volume fraction measurements in flames doped with large hydrocarbons

Abstract

Developing diesel surrogates that mimic the essential characteristics of target fuels such as their sooting tendency and volatility is a necessary but challenging endeavor, owing in part to the scarcity of available experimental sooting data for compounds in the appropriate high molecular weight range. To address this, in this work we demonstrate an experimental approach which provides quantitative sooting data for such compounds. Speci cally, we have measured spatially resolved two-dimensional soot volume fraction distributions for three large hydrocarbons: , ,-triisopropylbenzene (), , ,-triisopropylcyclohexane (), and perhydrophenanthrene (), as well as benzene and n-hexane. Measurements were performed in methane/air co owing ames whose fuel was doped separately with these compounds (dopant mass fraction .). Color-ratio pyrometry was used to measure soot temperature and soot volume fraction distributions. Sooting tendencies were > benzene > > > hexane. ese data are expected to be useful in formulation of surrogates with greater delity to the volatility and sooting characteristics of real diesel, and in validation of numerical soot models involving such surrogates.

Improved methodology for performing the inverse Abel transform of flame images for color ratio pyrometry

“…All the other conditions (assumed σ ads for soot, raw flame image, the T look-up table) were identical. The soot temperatures are in a similar range as the ones reported for similar co-flow diffusion flames using different fuels [13,16]. All three methods (FLiPPID, BASEX, onion-peeling with Tikhonov regularisation) gave qualitatively similar temperature distributions.…”

“…5b. The maximum value of f v was around 1.1 ppm, which is in between values reported for coflow diffusion flames fed with methane ( 0.08 ppm [13,40]) and ethylene ( 5-8 ppm [16,36]) and similar to a nitrogen diluted n-heptane flame operated at 2 bar (0.8 ppm) [41]. Among the three methods for Abel inversion, the new FLiPPID method led to significantly smoother profiles.…”

“…The optical properties of soot are beyond the scope of this work and the most commonly used dependence in the field [13,16,36], λ 2 σ ads (λ) ∝ λ −1.38 , was used. Fig.…”

“…Whenever possible, non-intrusive techniques are preferred to avoid perturbation of the system. One such technique that has gained increasing attention in recent years, is colour ratio pyrometry [9,[13][14][15]. Here, the colour and intensity of the visible light emitted by hot soot are used to infer their temperature and volume fraction [16,17].…”

“…The noisy image reconstruction has a significant effect on the soot temperatures T and volume fractions f v computed from R. This is especially problematic if flame centre-line values are the desired quantity. For example, estimating sooting propensities of fuels with the yield sooting indices (YSIs) requires the maximum of f v , which is often in the flame centre [13,30,31].…”