Soot formation in non-premixed counterflow flames of butane and butanol isomers

Abstract

Soot formation processes for butane and butanol isomers have been experimentally investigated and compared in a counterflow non-premixed flame configuration at atmospheric pressure. Nonintrusive laser-based diagnostic techniques, including Laser Induced Incandescence and Light Extinction, have been adopted for soot volume fraction measurements. Experimental results of these C 4 fuels have been compared to illustrate the effects of hydroxyl (-OH) group and the isomeric structures on soot formation process. Under the investigated conditions, butane isomers were observed to form more soot than butanol isomers, thereby showing the effect of the hydroxyl group. The effects of isomeric structural differences on sooting propensity were also observed within the butane and butanol isomers. In addition, while soot volume fraction was seen to increase with increasing fuel mole fraction, the ranking of sooting propensity for these C 4 fuels remained unchanged. Effects of varying strain rate and oxygen mole fraction on soot formation were studied herein as well. For each isomeric class, two chemical kinetic models available in the literature were used to simulate and compare the spatially-resolved profiles of the soot precursors. The amount of soot precursors predicted by the models were different and the initial fuel breaking pathways were also found to differ significantly. Furthermore, no direct correlation between the computed mole fractions of soot precursors and the measured amount of soot formed in the present experimental conditions was observed.

PAH formation in counterflow non-premixed flames of butane and butanol isomers

“…Both the fuel stream and the oxidizer stream were maintained at 400 K temperature. Further details on this counterflow burner facility can be found in [47][48][49] .…”

“…For the soot volume fraction measurements, the laser-induced incandescence (LII) technique was employed using the second harmonics (532 nm) of a Nd:YAG laser (Continuum Powerlite 8010), an ICCD camera (PI-MAX 3), and cylindrical optics. The present LII setup and the associated light extinction (LE) techniques for calibration have been described and discussed previously in [49] . For the PAH measurements, planar laser-induced fluorescence (PLIF) technique was used, involving a Nd:YAG-pumped dye laser (Continuum ND 60 0 0) and a UVT tracker, in addition to the equipments and instruments used for the LII measurements.…”

“…Since the LII technique used here has been described in details elsewhere [49] , the present focus is on the description of the PAH-PLIF technique for PAH measurements. The theoretical background behind the PAH-PLIF technique is as follows.…”

“…As mentioned earlier, the UV laser fluence was kept at low level of 250 mJ/cm 2 in the present study. Second, the detection of the PAH fluorescence signal was accomplished by integrating the prompt fluorescence signal, in a short detection gatewidth of 30 ns, right after the absorption of the laser pulse [2,49,56] . Since the fluorescence signal is short lived compared to the LII signal, the shorter detection gatewidth avoids the noise due to the LII signal (if any).…”

“…In the LII measurements, the ICCD camera detected 450 nm signal that was part of the broadband radiation generated by the soot particles. Reasons to select the 450 nm detection wavelength for the LII experiments were delineated in [49] . Detection wavelenghts of 334 nm, 400 nm, 450 nm, and 492 nm were used in the PAH-PLIF experiments.…”