Combustion adiabatic

Direct reaction of transition metals (Ti, Ta, Nb, Zr) or A1 or Si results in adiabatic combustion temperatures of 2500-A500 C. 

The liquid propellant rocket combination nitrogen tetroxide (N204) and IJDMII (unsymmetrical dimethyl hydrazine) has optimum performance at an oxidizer-to-fuel weight ratio of 2 at a chamber pressure of 67 atm. Assume that the products of combustion of this mixture are N2, C02, H20, CO, H2, O, H, OH, and NO. Set down the equations necessary to calculate the adiabatic combustion temperature and the actual product composition under these conditions. These equations should contain all the numerical... 

Equation (4.4), which connects the known variables, unbumed gas pressure, temperature, and density, is not an independent equation. In the coordinate system chosen, //, is (lie velocity fed into the wave and u2 is the velocity coming out of the wave. In the laboratory coordinate system, the velocity ahead of the wave is zero, the wave velocity is uh and (u — u2) is the velocity of the burned gases with respect to the tube. The unknowns in the system are U, u2, P2, T2, and p2. The chemical energy release is q, and the stagnation adiabatic combustion temperature is T, for n-> = 0. The symbols follow the normal convention. 

Note Twl, Volatilization temperature [or stoichiometric adiabatic combustion temperature creating compound under ambient conditions T = 298 K, P = 1 atm) Tg, Meta/ boiling point at 1 atm Te, Decomposition temperature (see... 

FIGURE 9.1 Adiabatic combustion temperature of various metal-oxygen/nitrogen systems as a function of equivalence ratio . Initial conditions 298 K and 1 atm. 

FIGURE 9.2 Equilibrium product composition and adiabatic combustion temperature for stoichiometric A1 and 02 at 298 K and 1 atm as a function of assigned enthalpy. An assigned enthalpy of zero corresponds to the true ambient condition. (1) specifies a liquid product, (s) specifies a solid product and all other products are gas. 

FIGURE 9.10 Comparison of the plot of adiabatic combustion temperature and product composition of the stoichiometric Al-Q2 system at total pressure of 1 atm (Fig. 9.2) and that at 10 atm. 

FIGURE 9.12 Adiabatic combustion temperature of a stoichiometric Al—02 system containing various amounts of die inert diluent argon as a function of assigned enthalpy, other conditions being the same as those for Fig. 9.2. 

Flame stability requires adiabatic combustion temperatures as high as 1600-1800 °C, which must be reduced to 1100-1450 °C by means of cooling bypass air before delivering the hot compressed gas to the turbine to avoid damaging the inlet blades. At such temperatures, within the tens milliseconds residence time required for complete burnout of fuel and CO, significant amounts of NO are produced, mostly by the Zeldovich thermal mechanism [2]. 

The variations of CH4 combustion activity associated with the PdO-Pd reversible transformation are responsible for the unique thermostating ability of palladium-supported catalysts. Indeed, in the adiabatic combustion of CH4, the... 

In the simple two-component system of PVC binder and oxidizer, the important propellant properties of specific impulse, density, adiabatic flame temperature, and burning rate increase with an increase in solids loading. This is shown in Figure 8, where theoretical calculated values of specific impulse, adiabatic flame temperature, and density are given for a range of oxidizer content for PVC plastisol propellants comprised of only binder and oxidizer. [Calculated values of specific impulse reported throughout this paper are for adiabatic combustion at a rocket chamber pressure of 1000 p.s.i.a. followed by isentropic expansion to 1 atm. pressure with the assumptions that during the expansion process chemical compo-... 

Assume that the combustion process occurs under well-mixed conditions. Use perfectly stirred reactor software together with the GRI-Mech mechanism (GRIM30. mec) to estimate the formation of NO in adiabatic combustion of CH4 with an excess-air ratio of 1.1... 

This reaction takes place in an adiabatic-combustion chamber, shown in Fig. 21.1. This chamber has no tubes to absorb radiant heat. 

Plenty of radiant heat is liberated, but only to the refractory brick walls. The bricks then reradiate the heat back into the gaseous products of reaction. This is called adiabatic combustion because no heat is lost from the combustion reaction to radiation. The adiabatic-combustion temperature for the preceding reaction [Eq. (21.1)1 is about 2300°F. The refractory used to contain this high temperature is manufactured from 90 percent alumina. Such refractory may be exposed to temperatures of up to 2900°F, without damage. 

During the strike, the sulfur plant was shut down for minor repairs. I had to supervise its start-up. Mainly, I had to reheat the adiabatic-combustion chamber to 1800°F, before restoring the flow of H2S. This was done by burning a controlled amount of methane or natural gas, with a carefully regulated flow of air. The idea was to slowly heat up the combustion chamber with hot flue gas by 100 to 200°F per hour. This slow reheat was needed to avoid cracking the refractory bricks, because of uneven heating. To carry away a portion of the heat of combustion of the natural gas, we used pipeline nitrogen. 

The quantity, h, in Equation 5 is not likely to be greatly different from its value in a plane adiabatic combustion wave. Taking x as the coordinate normal to such wave, h becomes the integral of the excess enthalpy per unit volume along the x-axis, so that the differential quotient, dh/dx, represents the excess enthalpy per unit volume in any layer, dx. Assuming the layer to be fixed with respect to a reference point on the x-axis, the mass flow passes through the layer in the direction from the unbumed, w, to the burned, 6, side at a velocity, S, transporting enthalpy at the rate Sdh/dx. Because the wave is in the steady state, heat flows by conduction at the same rate in the opposite direction, so that... 

Since we are located far from the boundary we may neglect the influence of heat transfer in the process. We equate the combustion temperature Tg with the so-called theoretical combustion temperature Tt, calculated from thermodynamic data under the assumption of adiabatic combustion. For more detail, see 1.4 and 1.5. 

Adiabatic Combustion and Autocatalysis by the End Products (In the Case of a Single Variable)... 

For the remaining elements, reference compounds have been chosen, as they occur in seawater or in the lithosphere, the earth s crust. An important aspect of this choice has been that the calculated exergy values of most compounds should be positive. Table 7.3 lists the standard chemical exergy values of the elements as presented in Szargut s well-known standard work [1]. Chapter 8 gives an example, the adiabatic combustion of H2, to illustrate the use of these exergy values in an interesting application. 

Pure hydrogen gas at room pressure and temperature is adiabatically combusted with air. The combustion takes place with an amount of air that is 30% in excess of what is stoichiometrically required. Calculate the adiabatic flame temperature of the process, the work lost, and the thermo-dynamic efficiency of the process. Assume air to consist of a mixture of 79 mol% of N2 and 21 mol% of 02. 

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