Flame Temperature and Combustion Products

The highest flame temperature for a B-GAP pyrolant is obtained at b( 0.2), whereupon BN is produced, while that for an Al-GAP pyrolant is obtained at ai( 0.4), whereupon AIN is produced. Al reacts with N2 generated by the decom- 

The reaction between Ti and Nj occurs in the low-temperature region at below Ti(0-2) for Ti-GAP pyrolants. On the other hand, the reaction between Ti and C occurs in the high-temperature region at above Ti(0-2). The reactions of Ti with N2 and C are represented by  

The maximum mole fraction of TiN is obtained at about xi(0 2), which also gives rise to the maximum flame temperature. The reaction of Ti and C occurs in the region above xi(0-2). The mole fraction of TiC increases with increasing xi- It is noted that the reaction between Zr and N2 produces ZrN in the region above lzr(0.5). 

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Table 6.7 Flame temperatures and combustion products of ethyl nitrate without and with lead tetramethyl (LTM) at 0.1 MPa.

From equation n. A. 23., it is seen that c depends mainly on conditions in the combustion chamber that is. the flame temperature and combustion product composition through ft and Y. The chamber pressure only indirectly influences c through its effect on T . ... 

When the oxidizer and fuel components are physically separated and allowed to diffuse into each other in the combustion zone, a diffusion flame is formed. Since the molecular distributions of the oxidizer and fuel components are not uniform, the temperature and combustion products are also not uniformly distributed in the combustion zone. Thus, the rate of the reaction generating the combustion products is low when compared to that in a premixed flame because an additional dif-fusional process is needed to form the diffusion flame. 

DIANP is a colorless liquid, which is soluble in acetone, methanol, dimethylformamide, DMSO, ethyl acetate, and benzene. It is not very soluble in water, ethanol, or butanol. DIANP is used in gun propellants and rocket propellants to reduce flame temperatures, toxic combustion products, smoke, and to increase performance without sacrificing bum rate. DIANP is an excellent substitute for nitroglycerine for gun propellants and rocket propellants. ... 

Gun Propellents. Although the stresses on individual gun propellant grains are less severe because of the small size, these propellants must withstand much higher weapon pressures and accelerations. Formulation options are usually more limited for gun propellants than for rocket propellants because the products of combustion must not foul or corrode a gun, should have a low flame temperature, and should exhibit minimum flash and smoke characteristics. Gun propellants are examined microscopically for porosity, are tested for mechanical characteristics, and fired in closed bombs to determine the burning characteristics. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

The first commercial oil-fumace process was put into operation in 1943 by the Phillips Petroleum Co. in Borger, Texas. The oil-fumace blacks rapidly displaced all other types used for the reinforcement of mbber and today account for practically all carbon black production. In the oil-fumace process heavy aromatic residual oils are atomized into a primary combustion flame where the excess oxygen in the primary zone bums a portion of the residual oil to maintain flame temperatures, and the remaining oil is thermally decomposed into carbon and hydrogen. Yields in this process are in the range of 35 to 50% based on the total carbon input. A broad range of product quaHties can be produced. 

The majority of the NOx produced in the combustion chamber is called thermal NOx. It is produced by a series of chemical reactions between the nitrogen (N2) and the oxygen (O2) in the air that occur at the elevated temperatures and pressures in gas turbine combustors. The reaction rates are highly temperature dependent, and the NOx production rate becomes significant above flame temperatures of about 3300 °F (1815 °C). Figure 10-19 shows schematically, flame temperatures and therefore NOx production... 

The ratio of rocket thrust to propellant mass flow, commonly called the specific impulse (/9p) of the propellant, represents a measure of the force developed per unit mass flow of propellant. From Eq. (2), it is apparent that high propellant-flame temperatures and low molecular-weight combustion products are required to produce high 7sp. 

Steam injection. Steam can be injected into the combustion zone as an inert material with the purpose of reducing the peak flame temperature and thereby reducing the NO formation. NO emissions can be reduced by typically 60% by steam injection. An obvious drawback is that the injected steam is lost to atmosphere. A side effect of the steam injection is that it increases the power output due to the higher mass flowrate through the turbine. Indeed, steam injection over and above that required for NO suppression can be used to increase power production during times of peak power demand. 

Radiation from flames and combustion products involve complex processes, and its determination depends on knowing the temporal and spatial distributions of temperature, soot size distribution and concentration, and emitting and absorbing gas species concentrations. While, in principle, it is possible to compute radiative heat transfer if... 

The inclusion of radiative heat transfer effects can be accommodated by the stagnant layer model. However, this can only be done if a priori we can prescribe or calculate these effects. The complications of radiative heat transfer in flames is illustrated in Figure 9.12. This illustration is only schematic and does not represent the spectral and continuum effects fully. A more complete overview on radiative heat transfer in flame can be found in Tien, Lee and Stretton [12]. In Figure 9.12, the heat fluxes are presented as incident (to a sensor at T,, ) and absorbed (at TV) at the surface. Any attempt to discriminate further for the radiant heating would prove tedious and pedantic. It should be clear from heat transfer principles that we have effects of surface and gas phase radiative emittance, reflectance, absorptance and transmittance. These are complicated by the spectral character of the radiation, the soot and combustion product temperature and concentration distributions, and the decomposition of the surface. Reasonable approximations that serve to simplify are ... 

Interactions between the flame and the surrounding wall (in a combustion chamber) could influence the contaminant production. This is examined by Dionisios Vlachos and his group at the University of Delaware (formerly at the University of Massachusetts at Amherst) using numerical bifurcation techniques (Chapter 26). For the first time, oscillatory instabilities have been found and control methodologies have been proposed to reduce flame temperatures and NO2 emissions. 

Table 2.2 Adiabatic flame temperatures and mole fractions of the combustion products of H2 and O2 mixtures at 2 MPa.

Fig. 4.15 Specific impulse, adiabatic flame temperature, and molecular mass of the combustion products for AP-GAP composite propellants.

Nitramine composite propellants composed of HMX or RDX particles and polymeric materials offer the advantages of low flame temperature and low molecular mass combustion products, as well as reduced infrared emissions. The reduced infrared emissions result from the elimination of COj and H2O from the combustion products. To formulate these composite propellants, crystalline nitramine monopropellants such as HMX or RDX are mixed with a polymeric binder. Since both HMX and RDX are stoichiometrically balanced, the polymeric binder acts as a coolant, producing low-temperature, fuel-rich combustion products. This is in contrast to AP composite propellants, in which the binder surrounding the AP particles acts as a fuel to produce high-temperature combustion products. 

Triple-base propellants are made by the addition of crystalUne nitroguanidine (NQ) to double-base propellants, similar to the way in which nitramine is added to CMDB propellants as described in the preceding section. Since NQ has a relatively high mole fraction of hydrogen within its molecular structure, the molecular mass of the combustion products becomes low even though the flame temperature is reduced. Table 4.13 shows the chemical composition, adiabatic flame temperature, and thermodynamic energy,/ as defined in Eq. (1.84), of a triple-base propellant at 10 MPa (NC 12.6% N). 

Figs. 11.1 and 11.2 show the adiabatic flame temperature, and the mole fractions of combustion products, respectively, as a funchon of the mass fraction of Mg designated by The maximum Tf is obtained at Mg(0-33). The major combustion products at the maximum I are C(s, and MgF2(g). The mass fractions c(s) and MgF2(g) decrease while Mg(g) and MgF2(L) increase with increasing g- When l g is increased further, above ]y[g(0.66), lMg(g) and lMgF2(L) start to decrease. 

Boron particles are incorporated into GAP pyrolants in order to increase their specific impulse.[8-i2] xhe adiabatic flame temperature and specific impulse of GAP pyrolants are shown as a function of air-to-fuel ratio in Fig. 15.10 and Fig. 15.11, respectively. In the performance calculation, a mixture of the combustion products of the pyrolant with air is assumed as the reactant. The enthalpy of the air varies according to the velocity of the vehicle (or the relative velocity of the air) and the flight altitude. The flight conditions are assumed to be a velocity of Mach 2.0 at sea level. An air enthalpy of 218.2 kj kg is then assumed. 

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,... 

NENAs possess good thermal stability, readily plasticize NC and other binders, generate low molecular weight combustion products and impart favorable impact sensitivity. Butyl NENA has edge over others because it imparts better low temperature properties as well [182]. The use of NENAs as plasticizers in gun and rocket propellant formulations imparts excellent properties such as high bum rates, reduction in flame temperature and molecular mass of combustion products and high force constant or specific impulse [183]. 

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