Soot production

The reaction gas is rapidly quenched with injected water at the point of optimum yield of acetylene, which happens to correspond with the point of maximum soot production. Coke will deposit on the walls of the burner and must be removed from time to time by a scraper. 

Images of the rapid-burn phase of combustion in a DISI engine. Stratification of the fuel distribution leads to areas of rich combustion and high soot production, as evidenced by areas of intense flame signal. 

The evidence suggests that temperature is the major parameter governing the extent to which a given fuel will soot under a particular flame condition or combustion process. As emphasized earlier, increasing the temperature under premixed fuel-air conditions decreases soot production, whereas the opposite is true for diffusion flames. The main effect of varying pressure must be manifested through its effect on the system temperature. Fuel pyrolysis rates are a... 

The reduction in H concentration leads to a decrease in OH and hence to an increase in soot production. 

As additives to reduce soot output in flames, metal and organometallic compounds, such as ferrocene, have attracted the attention of many investigators (see Ref. [113]). The effect in premixed flames is best described by Bonczyk [114], who reported that the efficiency with which a given metal affects soot production characteristics depends almost exclusively on temperature and the... 

Measurements showed that the amount of soot produced by the flame was affected by the mixing process between the air jet vortices, the fuel jets, and naturally entrained external air. PIV and smoke flow visualization showed that the air vortices induced strong external air entrainment into the main jet flow very close to the exit plane when the phase angle between the fuel jets and air jet were at the value for minimized soot production. When the wrong phase angle was used, i.e., that which leads to soot formation, the air vorticity coherence was reduced, the vortices appeared to develop further downstream, and the air entrainment at the flame base was significantly reduced. 

The loss of control due to interference with the external air entrainment process, resulting in an increased soot production as well as reduction in energy release, is significant especially in enclosed systems. 

Other issues of importance to combustor performance include soot production, pressure loss, and mechanical lifetime of the material. Too much soot in the exhaust could indicate poor combustion efficiency and unwanted particulate (smoke) emissions. For the baseline case without any inserts in the combustor, a slightly sooting flame was found. When one or two porous layers were inserted into the flame, no soot residue was found in the porous foams. It was thought... 

Before we examine the oxidation pathways available to aromatic systems, it is first instructive to review the most notorious role of these compounds in combustion chemistry their propensity to lead to soot formation. Soot is a byproduct of fuel-rich combustion, and soot particles can affect respiration and general health in humans." Soot production is a result of polycyclic aromatic hydrocarbon (PAH) formation in flames as reactive hydrocarbon radical intermediates combine to grow... 

Once the initial benzene ring has cyclized, it can undergo sequences of H-atom abstraction followed by acetylene addition, to yield PAHs. This is known as the H-abstraction-C2H2-addition (HACA) process, proposed by Frenklach and Wang. As an aromatic species aggregates to a size over 500 amu, it adopts a particulate form and can coalesce with other PAHs to further increase in size. When many of these particles agglomerate, they form soot. Efforts to minimize soot production are widespread. Notably, decreasing the carbon content relative to oxidizer concentration in a fuel/oxidizer mixture decreases the amount of soot formed. 

A variety of events that will lead to smoke production can occur in the pyrotechnic flame. Incomplete burning of an organic fuel will produce a black, sooty flame (mainly atomic carbon). A highly-oxidized fuel such as a sugar is not likely to produce carbon. Materials such as naphthalene (C loH s) and anthracene ( C i H 101 - volatile solids with high carbon content - are good candidates for soot production. Several mixtures that will produce black smokes are listed in Table 8. 1. 

The Arrhenius form of the reaction results from the Maxwell speed distribution and the rate at which molecular bonds in gas-phase species are broken [44], In full-scale fire modeling, the finite reaction rates must be considered if one attempts to model things such as CO and soot production and oxidation, or ignition and extinction. However, then the simple mixture fraction formulation must be supplemented by additional variables keeping track of the reaction progress. 

The physical and chemical properties of synthetic crudes are different from those of petroleum. Increased NO and soot production are the principal problems of the combustion of synthetic fuels, and control concepts for these two problems are in conflict. Fuel-rich combustion decreases NO but augments soot production, while fuel-lean combustion decreases (and can eliminate) soot production but augments NO emissions. Moreover, control procedures can affect combustion efficiency and heat-transfer distribution to the chamber surfaces. Table I, taken from Grumer (6), illustrates some specific relevant properties of synthetic liquid fuels and petroleum-based fuels. The principal differences between these fuels as related to their combustion behavior are summarized in Table II. 

Figure 5. Soot production in laminar and backmixed system for a toluene-air flame. From Wright (1968).

Constitutes feed to gasification reactor over and above the heavy fuel oil feedstock. Soot production is recycled 100% to gasification reactor. 

Near rich limits of hydrocarbon flames, soot is sometimes produced in the flame. The carbonaceous particles—or any other solid particles— easily can be the most powerful radiators of energy from the flame. The function k(t) is difficult to compute for soot radiation for use in equation (21) because it depends on the histories of number densities and of size distributions of the particles produced for example, an approximate formula for Ip for spherical particles of radius with number density surface emissivity 6, and surface temperature is Ip = Tl nrle ns) [50]. These parameters depend on the chemical kinetics of soot production—a complicated subject. Currently it is uncertain whether any of the tabulated flammability limits are due mainly to radiant loss (since convective and diffusive phenomena will be seen below to represent more attractive alternatives), but if any of them are, then the rich limits of sooting hydrocarbon flames almost certainly can be attributed to radiant loss from soot. 

Equation (42) cannot be used if NO concentrations approach their equilibrium values, since the net production rate then depends on the concentration of NO, thereby bringing bivariate probability-density functions into equation (40). Also, if reactions involving nitrogen in fuel molecules are important, then much more involved considerations of chemical kinetics are needed. Processes of soot production similarly introduce complicated chemical kinetics. However, it may be possible to characterize these complex processes in terms of a small number of rate processes, with rates dependent on concentrations of major species and temperature, in such a way that a function w (Z) can be identified for soot production. Rates of soot-particle production in turbulent diffusion flames would then readily be calculable, but in regions where soot-particle growth or burnup is important as well, it would appear that at least a bivariate probability-density function should be considered in attempting to calculate the net rate of change of soot concentration. 

Production of soot in hydrocarbon combustion is a complicated kinetic process involving transformations of fuel molecules in fuel-rich zones under the influence of heat (called pyrolysis) to produce new fuel molecules that contain more C and less H than the original molecules. The elementary steps involved are so numerous that simplifying approximations are essential for both efficient computation of soot production and development of understanding of the kinetic mechanisms. Progress is being made toward discovery of suitable simplications [49]. It is known that small... 

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