Temperature of combustion

Adiabatic flame temperature The highest possible temperature of combustion obtained under the conditions that the burning occurs in an adiabatic vessel, that it is complete, and that dissociation does not occur. 

Here Tc is the temperature of the cooling reservoir, i.e. the surroundings, while Th is the temperature of the process, i.e. the temperature of combustion. The Carnot efficiency is applicable for conventional heat pump engines. Efficiencies of more than 100 % correspond to converting heat from the surroundings into electricity and is only of academic interest, as is the high efficiency listed in Tab. 8.10. 

Setchkin, N.P., Self-ignition temperature of combustible liquids, J. Research, National Bureau of Standards, 1954, 53, 49-66. 

Changes in the moisture content of tobacco can affect the temperature of combustion within the hot coals and also the rate at which combustion occurs. Cigarettes must therefore he brought to equihhrium moisture content in a standard atmosphere. 

The dried and cured leaves of the nightshade plant Nkotiana tabaaim are known as tobacco. Tobacco is mostly smoked, less frequently chewed or taken as dry snuff. Combustion of tobacco generates approx. 4000 chemical compounds in detectable quantities. The xenobiotic burden on the smoker depends on a range of parameters, including tobacco quality, presence of a filter, rate and temperature of combustion, depth of inhalation, and duration of breath holding. 

Improved knowledge of chemistry at elevated temperatures is a general requirement since all energy use and transformation processs involve temperatures higher than normal. Requirements include thermochemical and kinetic data at the temperatures of combustion and conversion reactions of fossil fuels and at the more moderate temperatures of hot aqueous solutions. Improvements in theoretical models or empirical methods are required to allow more accurate extrapolation of knowledge and data from ordinary temperatures. 

In NO, smog formation (NO, is a mixture of NO, N2O, NO2, N2O4, and N2O5) the NO is produced by reaction of N2 and O2 at the high temperatures of combustion in automobiles and fossil fuel power plants, and NO2 and the other NO, species are produced by subsequent low-temperature oxidation of NO in air. NO is colorless, but NO2 absorbs visible radiation and produces brown haze. We write these reactions as a set of two reactions among four species,... 

The PAH shown in Figure 1 are typical of those produced from the combustion of various fuels ( ). Without exception, the combustion of almost any fuel will produce the suite of compounds shown in Figure 1. The relative abundances, however, can be substantially different depending on the temperature of combustion. 

It should be noted that Ba nitrate is preferable to K nitrate because the latter compound has a tendency to lower the temperature of combustion of the mixture... 

Just as for the heat, active centers diffuse from layer to layer as well. In a flame the entire interval of temperatures is realized, from the initial temperature to the temperature of combustion, and the reagent concentration varies simultaneously with the temperature. It is extremely important for us to trace here the variation of the chemical reaction rate. 

The exponent (14) describes the drop in the chemical reaction rate due to the drop in the temperature below the theoretical temperature of combustion. 

In the flame zone all temperatures lying in the interval between the initial temperature and the theoretical temperature of combustion, T0 reaction rate with increasing temperature according to the exponential law of Arrhenius leads to the result that the reaction in effect proceeds basically at high temperatures near Tv... 

The fact that the calorific value of the mixture L has appeared in the denominator is not in disagreement with the usual conceptions in fact, at a constant initial temperature T0, the theoretical temperature of combustion Tj entering into the formula increases with L, so that the velocity v increases as a whole. Conversely, an increase in L at constant corresponds to a drop in T0, so that the decrease in the velocity here is natural. 

We shall repeat the meaning and dimensions of all the notations Vg—linear velocity of flame propagation relative to the unburned mixture, cm/sec Ki—thermal conductivity at the theoretical temperature of combustion, cal/cm sec deg po—initial density of the mixture, g/cm3 n—concentration of the reacting substance, g/cm3 no—initial concentration of the reacting substance, g/cm3 L—calorific value of the mixture, cal/g To—initial temperature, deg Ti—theoretical temperature of combustion, T — To + L/c, deg E—heat of activation, cal/mole R—gas constant, cal/mole deg C—rate constant of a zero-order reaction, gr/cm3 sec C —rate constant of a first-order reaction, sec- 1 C"—rate constant of a second-order reaction, cm3/g sec. 

The criterion of homochronity tk/(P, where d is the characteristic dimension of the system, k is the thermal diffusivity and r is the characteristic time of the chemical reaction. Due to the strong dependence of the chemical reaction rate on temperature (see the next two criteria), it is necessary to define the temperature to which the quantity r relates. We will relate it to the theoretical temperature of combustion. 

The heat losses found above (30) lead to a decrease in the temperature of combustion by the quantity... 

In the simplest case of a mixture of gases which axe close in their properties the kinetic theory of gases asserts equality between the temperature of combustion and the temperature of the catalyst on whose surface the reaction runs to completion. Let us imagine a pellet of catalyst in an unbounded... 

All of what we have said above relates equally to the surface of a flame on which a rapid and full homogeneous chemical reaction takes place. In a lean hydrogen mixture on the surface of a flame at rest with respect to the gas to which hydrogen and oxygen are supplied by diffusion, a temperature significantly exceeding the theoretical temperature of combustion is established. 

Fig. 2 Dependence of the logarithm of the concentration of CCI4 on the theoretical temperature of combustion.

In exactly the same way, in the absence of thermal losses by radiation or cooling surfaces in the flame, and for equal thermal diffusivity and the diffusion coefficient, it may be shown that the temperature in the combustion zone of a diffusion flame T00 — (aft/i)a0b0/(aa0 + ftb0) is identically equal to the temperature of combustion at a constant pressure of a stoichiometric mixture of the gases under consideration. 

As we shall see below, almost the entire chemical reaction runs at a temperature close to the temperature of combustion. 

In slow flame propagation its velocity is determined by the maximum chemical reaction rate at a temperature close to the maximum temperature of combustion the zone of low temperature and small reaction rate is overcome by the action of heat conduction. 

Trinitronaphthalene appears to be a genuine stabilizer for nitrocellulose, a true inhibitor of its spontaneous decomposition. Marqueyrol found that a nitrocellulose powder containing 10 per cent of trinitronaphthalene is as stable as one which contains 2 per cent of diphenylamine. The trinitronaphthalene has the further effect of reducing both the hygroscopicity and the temperature of combustion of the powder. 

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