Optimized rate expressions for soot oxidation by OH and O2

Abstract

The two principal soot oxidizers in flames are the hydroxyl radical (OH) and molecular oxygen (O 2). Many soot oxidation rate expressions exist for these oxidizers, but they have considerable disparity and have not been sufficiently validated. To address this, twelve published experimental studies in diffusion flames, premixed flames, thermogravimetric analyzers, and flow reactors are examined. These are all the known studies that measured all of the following quantities at discrete locations: soot oxidation rate, temperature, OH concentration (if nonzero), and O 2 concentration. This yielded 160 measured soot oxidation rates spanning seven orders of magnitude. Optimized soot oxidation rate expressions for OH and O 2 are developed here by maximizing the coefficient of determination between measured and modeled oxidation rates. Oxidation of soot by OH is found to have a negligible activation energy and a collision

Experimental and soot modeling studies of ethylene counterflow diffusion flames: Non-monotonic influence of the oxidizer composition on soot formation

“…The soot oxidation by OH and O2 was also included. A constant collision efficiency γOH of 0.13 is assumed by OH radicals [78] while soot oxidation rates with O2 were taken from Celnik et al [79], although several recent studies suggested that the oxidation rates of soot depend on its chemical composition and internal structures [80][81][82][83]. Particle aggregation and fragmentation was not considered in this work.…”

Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines

“…First, it will decrease the availability of oxygen during the late cycle, which could limit the oxidation rate. It also lowers the flame temperature, slowing the chemical kinetics of the oxidation process as well as decreasing the formation of hydroxyl radicals (OH) [5], which is believed to be the main oxidizing species [6][7][8][9][10].…”

Reduced combustion mechanism for C1–C4 hydrocarbons and its application in computational fluid dynamics flare modeling

“…In the current soot oxidation model, partial-equilibrium (OH) model and instantaneous (O 2 ) model are used. Although there has been a long debate over the years about the selection of oxidizers for soot, recent studies have proven that for premixed and diffusion flames, the models indicate that soot oxidation by OH dominates over that by O 2 (Guo et al, 2016). The forming of soot in a flame is essentially a chemically controlled phenomenon.…”

“…The kinetics and mechanisms of soot oxidation have been studied for decades, and it was found that the primary soot oxidizers in the flame are OH radical and O 2 along with a few other minor species such as O radical (Khosousi and Dworkin, 2015;Siegla, 2013). Recent studies have shown that the OH radical plays much more important role than O 2 in soot oxidation (Lee et al, 2009;Guo et al, 2016). Discrete ordinate and P1 radiation models in ANSYS Fluent were tested separately to account for radiation losses in the flame.…”