Combustion-related reactions

A limitation of printed databases is that they may become outdated once published, they are unable to incorporate new information on kinetic parameters. The combustion specific databases listed above were published in the period 1973 to 1994 the most recent [23] covers the literature through 1992. This implies that data on combustion related reactions published since 1992 are not considered in these evaluations, and for a number of significant reactions the recommendations may be misleading. This deficiency of printed databases is to some extent overcome by the electronic database [256] offered by National Institute of Standards and Technology (NIST). The NIST database,1 which is regularly updated, also references most of the expert evaluations listed above. The drawback of using these kinds of data compilations is that the user may have to perform some data evaluation, that is, choose between data from various sources. 

Three areas of our studies covering photodissociation (by the absorption of single and multiple photons), electronic-to-vibrational energy transfer and combustion related reactions are discussed. Because of space limitation, we present primarily results obtained in this Laboratory and related work. 

CO laser probing of the vibratiopally excited CO formed in combustion-related reactions has proved valuable in gaining an understanding of the course of these reactions. Much useful data have been obtained pertinent to the determination of reaction mechanisms and the identity of intermediates taking part in the reactions. A number of reactions of O P) with allene, alkynes, carbon suboxide, and some free radicals are described below. 

The subject of chemical reactions under supercritical conditions is well outside the scope of matters of major concern to combustion related considerations. However, a trend to increase the compression ratio of some turbojet engines has raised concerns that the fuel injection line to the combustion chamber could place the fuel in a supercritical state that is the pyrolysis of the fuel in the line could increase the possibility of carbon formations such as soot. The... 

Numerous polymers autooxidize to form peroxides. These compositionally, and thus calorimetrically, ill-defined products may be considered polymeric peroxides. However, one well-defined polymeric peroxide is that of polystyrene with the repeat unit —CHa-CH(CeH5)-0-0-. Through a combination of combustion and reaction calorimetry (chain degradation to benzaldehyde and formaldehyde), a solid phase enthalpy of formation of this species was found to be 27 21 kJ mol . Much the same procedure was used to determine the enthalpy of degradation for the polyperoxide polymers of 2-vinylnaphthalene and the isomeric 1- and 2-propenylnaphthalene to form the related acylnaphthalene and formaldehyde. Numerically, the reaction enthalpy values for these last three polyperoxides were —206+4, —222 + 8 and —222 + 10 kJmol, to be compared with the aforementioned polystyrene with a value of —209 + 8 kJ mol. However, in the absence of enthalpy of formation data for the decomposition products in the naphthalene case, we hesitate to derive enthalpies of formation for these three species. ... 

The conception of the thermal propagation of a flame as the most common mechanism of combustion, related to successive ignition of the explosive mixture by heat generated in the reaction, is very far from new [1]. 

In the second manifold, the O2 is quantitatively converted to CO2 by combustion. The reaction occurs over several minutes by recirculation of the gas over Pt/graphite at 900°C. The C02 produced is condensed into a cold finger as it is formed the reaction is monitored through the pressure changes. Once the conversion is complete, the CO2 is transferred to second cold finger and its pressure determined using a capacitance manometer or strain gauge. The quantity of CO2 is directly related to the quantity of O2 present in the reaction solution and the isotope content is... 

High values of the activation energy E are examples of gas phase reaction, which can only proceed at a high temperature (examples are free radical reactions and combustion). Low values of E can be found in enzymes, cellular and life related reactions, and reactions that occur at room temperature. 

Organic polymers can also be incinerated as a means of disposal, (a) What products are formed on combustion of polyethylene (b) What products are formed on combustion of polyethylene terephthalate (c) Are these reactions exothermic or endothermic (See Sections 6.4 and 29.3 for related reactions.) (d) Propose a reason why HOPE and PET must be separated from poly(vinyl chloride) prior to incineration. 

Combustion and oxidation reactions produce oxygen atoms and hydroxyl and hydroperoxyl radicals as oxidizing agents. The first two have already been discussed. The hydroperoxyl radical, which was noted as an annoying interference in the attempts to determine the kinetics of hydroxyl radical chemistry, has been studied in far less detail, and the kinetics determined are not considered to be very accurate. What little experimental evidence that has accumulated is recorded in Table 42. The third entry in the table is an estimated collection of parameters derived to be consistent with those for related reactions, and probably these are much closer to the true values than are the experimental ones. 

The proper evaluation of the importance of atmospheric transformation of PAH will require a better understanding of the physical and chemical factors, which influence the reactivity of aerosol constituents during gas-particle interactions, e.g. particle size and specific surface, catalysis of the particle matrix. Thus, more elaborated kinetic and product identification studies are needed. These should not be limited to simplified model systems, but also include the direct exposure of combustion related particles in a reaction chamber to ambient levels of gaseous pollutants. 

The laminar flame jet flowing out of the nozzle has a configuration including a diffusion flame 1 (Fig. 11.7), a flame in a rich well-mixed mixture 2 and a flame in a lean well-mixed mixture 3. Those three different flame branches exist simultaneously. The flame base, called the triple point, is located along the stoichiometric contour and it can move when the flow parameters vary. Three spacially separated but related reaction zones coexist here the non-premixed mixture combustion occurs only in one of them. All three zones (branches) meet at the triple point. 

While OH and H are the main attacking radicals under most combustion-related conditions, other radicals also have some impact, and limited data are available for their reactions. The overall rate constant for reaction of OfP) with ethanol has been measured by several researchers. In 2007,... 

There are additionally a few studies that directly address biodiesel-related esters. Hayes and Burgess " " in 2009 explored hydrogen transfer reactions of the alpha peroxy radicals of MB and methyl pentanoate. Such reactions had been suggested by Herbinet et al. to be important in the early CO2 formation seen in methyl ester combustion. Hayes and Burgess were able to derive high-pressure rate expressions and considered a number of competing reactions as well. They also reported that composite G3B3 calculations matched available benchmark data on related reaction barriers with better accuracy than DFT approaches. 

Many combustion-related experiments as well as practical devices involve reaction in flowing gas streams. When reacting gas is moving, the kinetic energy of motion must be considered as part of the total energy that is conserved when chemical reaction releases heat energy. In essence, the flow velocity changes when reaction occurs. The differential equations that we use to describe the process must take this into account. 

The autocatalator model is in many ways closely related to the FONT system, which has a single first-order exothennic reaction step obeying an Arrhenius temperature dependence and for which the role of the autocatalyst is taken by the temperature of the system. An extension of this is tlie Sal nikov model which supports tliennokinetic oscillations in combustion-like systems [48]. This has the fonn ... 

Vehicle Fa.ctors. Because knock is a chemical reaction, it is sensitive to temperature and reaction time. Temperature can in turn be affected either by external factors such as the wall temperature or by the amount of heat released in the combustion process itself, which is directiy related to the density of the fuel—air mixture. A vehicle factor which increases charge density, combustion chamber temperatures, or available reaction time promotes the tendency to knock. Engine operating and design factors which affect the tendency to produce knocking are... 

Some concerns directly related to a tomizer operation include inadequate mixing of Hquid and gas, incomplete droplet evaporation, hydrodynamic instabiHty, formation of nonuniform sprays, uneven deposition of Hquid particles on soHd surfaces, and drifting of small droplets. Other possible problems include difficulty in achieving ignition, poor combustion efficiency, and incorrect rates of evaporation, chemical reaction, solidification, or deposition. Atomizers must also provide the desired spray angle and pattern, penetration, concentration, and particle size distribution. In certain appHcations, they must handle high viscosity or non-Newtonian fluids, or provide extremely fine sprays for rapid cooling. 

The radicals and other reaction components are related by various equiUbria, and hence their decay by recombination reactions occurs in essence as one process on which the complete conversion of CO to CO2 depends. Therefore, the hot products of combustion of any lean hydrocarbon flame typically have a higher CO content than the equiUbrium value, slowly decreasing toward the equiUbrium concentration (CO afterburning) along with the radicals, so that the oxidation of CO is actually a radical recombination process. 

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