Temperature-time data combustion reaction

The experiments are usually carried out at atmospheric pressure and the initial goal is the determination of the enthalpy change associated with the calorimetric process under isothermal conditions, AT/icp, usually at the reference temperature of 298.15 K. This involves (1) the determination of the corresponding adiabatic temperature change, ATad, from the temperature-time curve just mentioned, by using one of the methods discussed in section 7.1 (2) the determination of the energy equivalent of the calorimeter in a separate experiment. The obtained AT/icp value in conjunction with tabulated data or auxiliary calorimetric results is then used to calculate the enthalpy of an hypothetical reaction with all reactants and products in their standard states, Ar77°, at the chosen reference temperature. This is the equivalent of the Washburn corrections in combustion calorimetry... 

Using Eqs. (5.1) and (5.2), the heat flitx in zone II, n, and the heat flux in zone III (Ajii) are determined from temperature profile data in the combustion wave. As shown in Fig. 5.18, both n and Am increase linearly with increasing pressure in a log-log plot n p0 75 nd Am po-8o he heat of reaction in zone II, Qji, is determined as 624 kj kg b[44] It is noteworthy that the heat of reaction of HMX in zone II is 300 kJ kg even though the adiabatic flame temperature of HMX is 1900 K higher than that of GAP copolymer. Furthermore, Am of GAP is of the same order of magnitude as Am of HMX, despite the fact that n of GAP is approximately ten times larger than the n of HMX shown in Fig. 5.6. 

Burning times for coal particles are obtained from integrated reaction rates. For larger particles (>100 fim) and at practical combustion temperatures, there is a good correlation between theory and experiment for char burnout. Experimental data are found to obey the Nusselt "square law" which states that the burning time varies with the square of the initial particle diameter (t ). However, for particle sizes smaller than 100 p.m, the Nusselt... 

Many times we need to have the combustion or reaction data at a temperature at which the data are not normally reported in literature. By using Hess s Law and change in heat capacity values, the heat of reaction at temperature of interest can be calculated. 

This reaction plays a major role in determining the amount of CO produced by combustion systems but, despite its importance, until 1971 there was considerable controversy over the apparent discrepancy between rate constant studies at high and low temperatures. The general feeling prior to that time was that the reaction involved an atom transfer and that the rate data should conform to the equation... 

Much of the outstanding chemical investigation of the low-temperature combustion of alkanes was performed on the C5 and alkanes, in the late 1960s and early 1970s, mainly by Cullis and co-workers [137, 189-193] and Fish and co-workers [99, 194-199]. The quality and extent of the chemical analyses in these studies has rarely been equalled in subsequent work, and the data obtained provide very strong evidence, not only for the importance of alkylperoxy radical formation and isomerization in the low-temperature chemistry, but also the role of these reactions in the development of cool-flames and two-stage ignitions. However, one constraint on quantitative application is that much of the information was obtained under markedly non-isothermal conditions in the absence of any record of the reactant temperature. Moreover, the effects of convection on the movement of cool-flame combustion waves within an unstirred reaction vessel were not appreciated at the time [52], which casts doubt on some of the mechanistic interpretations of the evolution of multiple cool-flames that were made [195]. 

Until recently it was further assumed that the hydrocarbon oxidation reactions have equilibrated prior to the onset of NO formation because the NO reactions are relatively much slower (5) at temperatures of stoichiometric hydrocarbon-air combustion and because they take place over an extensive portion of the mixing region. Fenimore (6) and Harris et al. (7) have conducted recent experimental studies of NO formation in atmospheric flat flames their data support this simplified picture for posf-combustion-zone formation. However, Fenimore (6) noted a substantial amount of NO was formed very rapidly in the flame front of methane-air and ethylene-air flames but not in CO-air or H2-air flames. Figure 1 shows Fenimores data on NO formation in four ethylene-air flames as a function of reaction time from the burner surface to the probe tip. The positive intercepts are indicative of flame zone or prompt NO. Fenimore subsequently postulated that reactions such as... 

The use of thermogravimetric analysis (TGA) apparatus to obtain kinetic data involves a series of trade-offs. Since we chose to employ a unit which is significantly larger than commercially available instruments (in order to obtain accurate chromatographic data), it was difficult to achieve time invariant O2 concentrations for runs with relatively rapid combustion rates. The reactor closely approximated ideal back-mixing conditions and consequently a dynamic mathematical model was used to describe the time-varying O2 concentration, temperature excursions on the shale surface and the simultaneous reaction rate. Kinetic information was extracted from the model by matching the computational predictions to the measured experimental data. 

Thus, the data in Tables 2-4 can be used to calculate, with reasonable (or better) accuracy over a wide range of temperatures, thermodynamic properties of numerous reactions implicated in the combustion of boron- and aluminum-containing propellant formulations. The kinetics can be addressed as well, as was shown in a number of instances. The determination of transition states and activation barriers can be rather time-consuming. However computational methodology continues to improve (e.g. a new version of CBS-QB3... 

According to laboratory data, the quantity of air required for the combustion of the nascent fuel in low-temperature oxidation reactions can attain 40.3 m3 per 100 kg of reservoir rock (c urve 1 on Fig. 60). This amount is almost three times greater than the volume of air required in high temperature combustion. 

Peroxy radicals ROO are key species in the mechanisms of oxidative and combustion systems. At the same time they have been among the most difficult radicals to study experimentally. There are only limited or no thermochemical information available for unsaturated alkylperoxy and hydroperoxide species. An explanation for this paucity of data could be the fact that these species are unstable and short-lived, and therefore difficult to study and characterise by experimental methods. The difficulty arises in part from the lability of these radicals towards reversible unimolecular dissociation into R + O2 and then to reversible isomerization into hydroperoxy alkyl radicals ROOH, both of these reactions occurring at comparable rates at temperatures below 450 K [2]. 

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