Flame temperature calculations

In the same context as the heat of formation, the JANAF tables have tabulated most conveniently the equilibrium constants of formation for practically every substance of concern in combustion systems. The equilibrium constant of formation (KPt[) is based on the equilibrium equation of formation of a species from its elements in their normal states. Thus by algebraic manipulation it is possible to determine the equilibrium constant of any reaction. In flame temperature calculations, by dealing only with equilibrium constants of formation, there is no chance of choosing a redundant set of equilibrium reactions. Of course, the equilibrium constant of formation for elements in their normal state is one. 

The flame temperature calculation is essentially the solution to a chemical equilibrium problem. Reynolds [8] has developed a more versatile approach to the solution. This method uses theory to relate mole fractions of each species to quantities called element potentials ... 

The heat of combustion amounts to 7483 cal/g of aluminum fuel and the adiabatic flame temperature calculated by the NASA chemical equilibrium program [6] is 4005 K. The combustion equation for aluminum and steam is... 

The heat of combustion amounts to 4272 cal/g of aluminum fuel and the adiabatic flame temperature calculated by the chemical equilibrium program is 3036 K. Thus, the heat released when aluminum is burned with steam is about 57% of the amount released when aluminum is burned with O2. Many experimental investigations have been carried out on the combustion of aluminum in atmospheres where the primary oxidizer was O2 [7-16], and also in atmospheres where the primary oxidizer was H2O and/or CO2 [16-19]. There is general... 

From equation n. B. 26. above one sees that the proper quotient of molar concentration or mole fractions does depend on pressure. For flame temperature calculations, it is most convenient to write Kp in terms of the nt. The special case of ... 

In Section A.l, the general laws of thermodynamics are stated. The results of statistical mechanics of ideal gases are summarized in Section A.2. Chemical equilibrium conditions for phase transitions and for reactions in gases (real and ideal) and in condensed phases (real and ideal) are derived in Section A.3, where methods for computing equilibrium compositions are indicated. In Section A.4 heats of reaction are defined, methods for obtaining heats of reaction are outlined, and adiabatic flame-temperature calculations are discussed. In the final section (Section A.5), which is concerned with condensed phases, the phase rule is derived, dependences of the vapor pressure and of the boiling point on composition in binary mixtures are analyzed, and properties related to osmotic pressure are discussed. 

The adiabatic flame temperature calculated from the stoichiometry was 1000 °K, while the measured value was 923 °K the difference being almost certainly due to heat losses from the 0.05 cm diameter thermocouple used. The residence time in the reaction zone under the conditions employed was approximately 3 x 10 sec which was long enoi h for appreciable self-decomposition to have taken place. For a brief discussion of the likely mechanism, see Sect. 4.2... 

The flame temperature calculated on the basis of this stoichiometry is about 1100 °C, in excellent agreement with the observed value [127]. 

YOURSELF 2. Suppose Tau is the adiabatic flame temperature calculated for a given fuel + air feed to a... 

The starting point in development of an ammonia flame mechanism was a mechanism previously used to model ammonia oxidation in a flow tube near 1300 K ( ). Additional reactions were added that were thought to be important at the higher flame temperatures. Calculations with this mechanism produced profiles in marked disagreement with our data. The predictions were slower than observed decay of NH species was much too slow, and OH peaked too late by about 2.5 mm. To make matters worse, far too much NO was formed. The NO problem was especially troublesome in that attempts to increase the rate of NH decay only served to produce even more NO, since NO was the primary decay channel for the NHi species. A possible resolution of this dilemma involves reactions of the NHi species with each other to form N-N bonds. These complexes could then split off H atoms to ultimately form N2. 

Equation 12 can be solved for the quasi-adiabatic flame temperature at standard temperature and pressure (STP). For (p < 0.2, the flame temperatures calculated using equation 12 are in the range Tf = 1720-1420 K, compared to experimental values T( = 1600 100 K (11,12). Equation 12 shows that the lower flammability limit corresponds to a temperature T 1600 K at which the rate of heat losses from the flame equal the rate of heat production in the flame owing to the combustion reactions. 

---