The Role Of Soot Particle Formation On The Production Of Carbon Monoxide In Fires

Abstract

A systematic study of the effects of soot formation on the production of carbon monoxide (CO) in laminar diffusion flames has been conducted. Increased amounts of soot have been observed to result in larger concentrations of CO in the higher regions of the flames. Comparisons of CO state relationships as a function of local equivalence ratio show distinct effects as the local soot volume fraction is varied. Fuel rich regions exhibit lower CO mole fractions as soot concentration increases, whereas higher CO mole fractions are observed under fuel lean conditions. Radiative quenching and competition between soot and CO for OH are examined. Competition for OH is a plausible mechanism that can be responsible for the high CO emissions from fires. Radiative quenching does not seem to playa significant role in fuel rich regions but can be important under fuel lean conditions.

Smoke Emissions in Fires

“…It is well known that soot fraction in smoke depends on the hydrogen atom fraction in the fuel [2,5,7,[15][16][17]. Data used in this paper supports this as shown in Fig.…”

“…It is thus suggested that there is a similarity between the kinetic and air-fuel mixing processes that govern the formation and oxidation of both CO and soot [5,7,8]. However, the ratio is not a constant and increases for highly charring, highly halogenated and highly fire retarded fuels with negligible or no hydrogen atoms in the structure and for the under-ventilated fires.…”

“…Fully ventilated combustion data show that CO and soot emissions are correlated and the ratio of their emission rates (or yields) is a constant [2][3][4][5][6][7][8][9][10]. It is thus suggested that there is a similarity between the kinetic and air-fuel mixing processes that govern the formation and oxidation of both CO and soot [5,7,8].…”

“…It is generally accepted that CO and soot compete for free radicals, especially OH and O and thus their formation and emission depend on the availability of free radicals [2][3][4][5][6][7][8][9]. The following overall kinetics for the soot and CO emission has been suggested [2]:…”

Experimental study of the effects of fuel type, fuel distribution and vent size on full-scale underventilated compartment fires in an ISO 9705 room

“…Measurements by Koylu et al [46] and Puri and Santoro [47] showed that there is a linear relation in the emission of soot and CO from buoyant turbulent diffusion flames burning various hydrocarbon fuels (acetylene, propene, etc.). Measurements in the fuel lean (overfire) plume region of hydrocarbon fires showed that the soot and CO generation factors (η S and η CO ) tended to increase with flame residence time, until a near-constant value was reached after long times (compared to the smoke point).…”