Flame temperature, fuel burning

Theoretical Studies of Liquid-Propellant Rocket Instability , Ibid, pp 1101-28 Pj) G.A. McD. Cummings A.R. Hall, "Perchloric Acid Flames Premixed Flames With Methane and Other Fuels , Ibid, 1365-72 P2) D.J. Carlson, Emittance of Condensed Oxides in Solid Propellants Combustion Products , Ibid, 1413-24 Qj) Ibid, "Perchloric Acid Flames Some Flame Temperatures and Burning Velocities , Ministry of Aviation,... 

The mixture ratio R is a volume concentration of index fuel (CO + H2) relative to the sum of index and limit fuels, where the limit fuel is CO + CH4 or H2 + CH4. Mixtures having the same value of MN yield the same composition of combustion products and adiabatic flame temperature when burning stoichio-metrically with air. This choice was made in order to assess whether adiabatic flame temperature and final composition were significant factors in explaining differences of behavior for different fuel compositions. Additional details on the selection of gas mixtures composition can be found in Reference (9). 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

Flame Temperature. The adiabatic flame temperature, or theoretical flame temperature, is the maximum temperature attained by the products when the reaction goes to completion and the heat fiberated during the reaction is used to raise the temperature of the products. Flame temperatures, as a function of the equivalence ratio, are usually calculated from thermodynamic data when a fuel is burned adiabaticaHy with air. To calculate the adiabatic flame temperature (AFT) without dissociation, for lean to stoichiometric mixtures, complete combustion is assumed. This implies that the products of combustion contain only carbon dioxide, water, nitrogen, oxygen, and sulfur dioxide. 

Surface combustion devices are designed for fully premixing the gaseous fuel and air and burning it on a porous radiant surface. The close coupling of the combustion process with the burner surface results in low flame temperatures and, consequently, low NO formation. Surface materials can include ceramic fibers, reticulated ceramics, and metal alloy mats. This approach allows the burner shape to be customized to match the heat transfer profile with the application. 

Moreover, because all fuels burn, POX does not demand a catalyst, although advanced designs often use one to lower flame temperatures, which helps to relax materials requirements and to improve efficiency and emissions. The hydrogen concentration, however, is considerably lower (—40%) because... 

Figure 20, a magnitude schematic view of zone 1 in Fig. 19, depicts this effect. These exothermic oxidative reactions in zone 1 can release sufficient heat to expel partially combusted products, pyrolysis products, and fuel and oxidizer fragments into the gas phase, where they can intermix and burn completely. The maximum flame temperature will then be reached in the luminous zone, where the largest portion of the heat is released. However, a relatively... 

The terrperature of the hot layer in the corridor is shown in Figure 7. In the corridor, the hot gas is untenable for an upright person next to the open fire room door after about 160 seconds. After about four minutes, the radiation from the hot layer would be too high to permit a person to pass. Furthermore, in actual fact, the temperature would be higher than that calculated at the fire room door, because of the fuel which would burn in the corridor, thus providing flame temperature radiation in addition to the hot layer temperature computed here. 

Fuel gas Support gas Burning velocity/m s 1 Flame temperature/K... 

Example 3.4 A turbulent fire plume is experimentally found to bum with 10 times the required stoichiometric air up to the tip of the flame. It is also measured that 20 % of the chemical energy is radiated to the surroundings from the flame. The fuel is methane, which is supplied at 25 °C and burns in air which is also at 25 °C. Calculate the average temperature of the gases leaving the flame tip. Assume constant and equal specific heats and steady state. 

For our estimations and the adiabatic control volume in Figure 4.10, 7b should be the adiabatic flame temperature. Consider a fuel-lean case in which no excess fuel leaves the control volume. All the fuel is burned. Then by the conservation of species,... 

Once ignition has occurred in a mixture of fuel and oxidizer, propagation will continue, provided the concentrations are sufficient and no disturbance results in excessive cooling. The zeroth-order rate model is assumed to represent the lean case. Substituting the selected properties into Equation (4.43), the net release and loss curves are plotted in Figure 4.22 as a function of the flame temperature. The initial temperature of the mixture is 25 °C and fuel mass fractions are 0.05 and 0.03, representative of stoichiometric and the lower limit respectively. At this lower limit, we should see that a steady solution is not possible, and the calculations should bear this out. The burning rate is evaluated at the flame temperature, and 6K is found from Equation (4.44) with Su at the flame temperature... 

Let us reconsider the critical flame temperature criterion for extinction. Williams [25], in a review of flame extinction, reports the theoretical adiabatic flame temperatures for different fuels in counter-flow diffusion flame experiments. These temperatures decreased with the strain rate (ua0/x), and ranged from 1700 to 2300 K. However, experimental measured temperatures in the literature tended to be much lower (e.g. Williams [25] reports 1650 K for methane, 1880 K for iso-octane and 1500 K for methylmethracrylate and heptane). He concludes that 1500 50 K can represent an approximate extinction temperature for many carbon-hydrogen-oxygen fuels burning in oxygen-nitrogen mixtures without chemical inhibitors . 

It is estimated that in the WTC disaster that the jet fuel burned in one of the towers at 10 GW. If this is assumed to bum over an equivalent circular area constituting one floor of 208 x 208 ft, and would produce an unimpeded fire plume, then compute the height of the flame and the temperature at two diameters above the base. 

If the fuel responds fast to the compartment changes, such a quasi-steady burning rate model will suffice to explain the expenditure of fuel mass in the compartment. The fuel heat flux is composed of flame and external (compartment) heating. The flame temperature depends on the oxygen mass fraction ( Yq2 ), and external radiant heating depends on compartment temperatures. 

Consider a fuel burning in inert airs and oxygen where the combustion requirement is only 0.21 moles of oxygen. Order the following mixtures as to their adiabatic flame temperatures with the given fuel. 

The stirred reactor may be compared to a plug flow reactor in which premixed fuel-air mixtures flow through the reaction tube. In this case, the unbumed gases enter at temperature T0 and leave the reactor at the flame temperature T. The system is assumed to be adiabatic. Only completely burned products leave the reactor. This reactor is depicted in Fig. 4.50. 

Three parameters are generally evaluated the mass burning rate (evaporation), the flame position above the fuel surface, and the flame temperature. The most important parameter is the mass burning rate, for it permits the evaluation of the so-called evaporation coefficient, which is most readily measured experimentally. 

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