Combustion kinetic rate

E.M. Coal pyrolysis experiments, kinetic rates and mechanisms, Prog. Energy Combust. Sci., 18, 133-220, (1992). 

In the case of heterogeneous surface burning of a particle, consideration must be given to the question of whether diffusion rates or surface kinetic reaction rates are controlling the overall burning rate of the material. In many cases, it cannot be assumed that the surface oxidation kinetic rate is fast compared to the rate of diffusion of oxygen to the surface. The surface temperature determines the rate of oxidation and this temperature is not always known a priori. Thus, in surface combustion the assumption that chemical kinetic rates are much faster than diffusion rates cannot be made. 

Platinum was historically used as an additive to increase the rate of CO combustion in the catalyst bed. Lack of Pt in the circulating catalyst inventory could reduce overall combustion kinetics. Most units would operate with 1 ppm Pt on E-cat. Others have to operate much higher due to inherent design problems. Some... 

The combustion reaction rate is controlled both by the availability of fuel and oxygen kinetic effects (temperature). In full-scale fire modeling, the resolvable length and time scales are usually much larger than those associated with the scales of the chemical combustion reaction, and it is common to assume that the reactions are infinitely fast. The local reaction rate depends on the rate at which oxygen and fuel are transported toward the surface of stoichiometric mixture fraction, shown in Figure 20.2 as a point where both oxygen and fuel mass fractions go to zero. For almost 20 years, the EBU or eddy dissipation models were the standard models used by the combustion CFD community. With the EBU, in its simplest form, the local rate of fuel consumption is calculated as [3] ... 

Most, if not all, solutions of the nozzle expansion problem have used equilibrium composition chamber conditions as the initial condition for nozzle solution. The feature is common to all of the nozzle flow solutions that is, the equilibrium composition expansion, frozen composition expansion, Bray freezing model, and kinetic rate solutions have all invoked the assumption of equilibrium composition at the beginning of the expansion process. While the failure to obtain equilibrium composition predicted performance, in terms of experimental characteristic velocities, has suggested a departure from equilibrium in the combustion chamber, only recently have non-equilibrium compositions been measured directly (31). 

The technique for coupling the chemical kinetic rate equations to the combustion process taking place in a rocket combustion chamber has not been devised. A detailed solution of the combustion chamber kinetics problem requires combination of the relations governing mixing, droplet burning, chemical reaction rates and combustion chamber flow characteristics. It is neither obvious that the complete solution to the complex combustion kinetics problem is possible nor that the efforts in this direction are wisely undertaken on the basis of present understanding of the more fundamental processes. 

According to the Semenov theory of chain reactions [2] the rate of oxidation depends strongly (half to first power) on the rate of production of new chain centres. However, the problem that has bedevilled combustion kinetics over many years is the chemical nature of the process. Reactions (1) and (lA) are the primary initiation reactions in hydrocarbon oxidation, to be distinguished from secondary initiation processes such as reaction (13) where radicals are produced from a stable intermediate... 

The distribution of water and hydrogen as products of the hydrocarbon combustion described by reaction Cl is calculated from the water-gas-shift equilibrium. All reactions are treated as irreversible reactions and the kinetic rates of the reactions (Cl - C3 are taken from (11],... 

Control of oil shale char combustion is more easily managed if there is a knowledge of how the rate of combustion depends on (>2 concentration and temperature. This motivation led to an earlier study (6) of the combustion kinetics of spent shale from the Parachute Creek Member in western Colorado. That study... 

Char combustion kinetics have been previously reported for Antrim shale by Rostam-Abadi and Mickelson (9). In that study the authors reported that the rate was second order with respect to the char remaining and that there was noticeable chemisorption of (>2 Attempts to fit our data for the Antrim shale to a second order rate expression were unsuccessful and, in all cases, the data appeared to follow first order kinetics. Although we did not have the precision to measure O2 chemisorption, this phenomenon is consistent with our previous observations (6 ) of catalytic activity in those shales containing decomposed mineral carbonates. That is, the catalytic activity of CaO was attributed to its ability to chemisorb 02 As will be discussed in more detail below, the Antrim shale sample did not contain such carbonates and no catalytic behavior was observed. However, the magnitude of the rate constants reported by Rostam-Abadi and Mickelson (9) are very similar to those measured here. 

Antal, M. J. Friedman, H. L. Rogers, F. E. Kinetic Rates of Cellulose Pyrolysis in Nitrogen and Steam , to appear in Combustion Science and Technology, 1979. 

The model eonsiders the most important reactions for the start-up. The combustion of the key components CO, propene, propane and hydrogen is described by kinetic rate expressions according to the following reaction scheme ... 

Additives, inhibition of detonation, 186-90 Air jet surface, I69f Aliphatic flames, formation of aromatic species, 3-16 Allene, rate coefficients for cyclopentadienyl cation reactions, 59t,60t,6lt Ammonia combustion, kinetic mechanism, 93,94f... 

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