Temperatures flame combustion

Combustion (Flame) Temperature of Propellants Measurements. Optical methods are the most widely used for the measurement of flame temperature. Since the study of a flame depends not only on temperature, but also on other factors (the radiation factor, the chemical reactions in the gases, etc), it is necessary first of all to study the spectral characteristics of the objects under investigation. Flame spectra were studied in Russia on the ISP-51 spectrograph... 

The primary component of the hypersonic flame spraying process is an internal combustion device, which produces an "exhaust" similar to that found in a rocket. This exhaust is produced by the internal combustion of oxygen and fuel gases. A combustion flame temperature of approximately 5500°F. is created, with exhaust velocities of 4,500 feet per second. 

Nitrogen Oxides, These compounds result from all fossil-fuel combustion processes where air is used as the oxidant. Oxygen from the air and nitrogen combine at combustion flame temperatures to form nitnc oxide,... 

Exhaust Gas Recirculation. In one method of NO emission control, exhaust gas is fed back into the inlet manifold and mixed with the fuel and inlet air. The resultant mixture upon combustion in the cylinder results in lower peak combustion temperature and lower NO formation because the reaction of N2 + 0-, — NOx is strongly dependent on the combustion flame temperature (99,109—112). The degree of NO depression is dependent on the amount of exhaust gas recirculation (EGR) as shown in Figure 13. EGR provides a diluent gas having high molecular weight and C02 which absorbs heat. Also, EGR affects the flame speed of the mixture, and thus provides a certain antiknock quality to the combustion process. The impact of EGR on engine parameters has been detailed (113). 

None the less, by maintaining condition for efficient combustion, flame temperature may reach close to the theoretically calculated temperature. 

In the early stages of the Clean Air Act, the catalyst was required only to abate HC and CO, since the NO standard was relaxed such that exhaust gas recycle (EGR) could be used to meet the NO standards. EGR dilutes the combustion gas and lowers the combustion flame temperature and hence the thermal NO formation, as predicted by the Zeldovich mechanism (2). Operating the engine just rich of stoichiometry further reduced the formation of NO, and secondary air was pumped into the exhaust gas to provide sufficient O2 for the catalytic oxidation of HC and CO on the catalyst. 

Oxygen does not bum, but supports and accelerates combustion. However, high concentration oxygen atmospheres substantially increase combustion rates of other materials, and may form flammable mixtures with other combustibles. Flame temperatures in oxygen are higher than those in air. 

Hence, AnRT = 50 x 8.314 x 673 = 280 kJ. The heat of combustion of octane is 5,470 kJ/mol. This extra work of compression is only about 5% of the combustion energy. However, the calculated adiabatic combustion flame temperature for octane in air is about 1,400 K, whereas in oxygen, the flame temperature is over 9,000 K. This represents a substantial increase in energy of combustion due to the removal of nitrogen. 

The study on the spray combustion characteristics of 10% CPO blended with diesel fuel was conducted in a constant-volume combustion chamber. With the fixed experimental conditions such as spray ambient pressure and injection events, the effects of 10% CPO diesel at the injection line pressure of 100 MPa on spray combustion and flame stmcture were investigated using a photo diode and ICCD camera. Two-color method was also employed to predict combustion flame temperatures and KL factors. 

Figure 23.7 Spray combustion flame temperature distribution.

Figure 6.28 Increasing the theoretical flame temperature by reducing excess air or combustion air preheat reduces the stack loss.

Example 6.4 The process in Fig. 6.2 is to have its hot utility supplied by a furnace. The theoretical flame temperature for combustion is 1800°C, and the acid dew point for the flue gas is 160°C. Ambient temperature is 10°C. Assume = 10°C for process-to-process heat transfer but = 30°C for flue-gas-to-process heat transfer. A high value for for flue-gas-to-process heat... 

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. 

Where T)is flame temperature in K MC is moisture content of the waste, expressed on a total weight basis SR is defined as stoichiometric ratio or moles O2 avadable/moles O2 required for complete oxidation of the carbon, hydrogen, and sulfur in the fuel, ie, 1/SR = equivalence ratio and is temperature of the combustion air, expressed in K. In Fnglish units, this equation is as follows ... 

The combustible components of the gas are carbon monoxide and hydrogen, but combustion (heat) value varies because of dilution with carbon dioxide and with nitrogen. The gas has a low flame temperature unless the combustion air is strongly preheated. Its use has been limited essentially to steel (qv) mills, where it is produced as a by-product of blast furnaces. A common choice of equipment for the smaller gas producers is the WeUman-Galusha unit because of its long history of successful operation (21). 

Figure 4 illustrates the trend in adiabatic flame temperatures with heat of combustion as described. Also indicated is the consequence of another statistical result, ie, flames extinguish at a roughly common low limit (1200°C). This corresponds to heat-release density of ca 1.9 MJ/m (50 Btu/ft ) of fuel—air mixtures, or half that for the stoichiometric ratio. It also corresponds to flame temperature, as indicated, of ca 1220°C. Because these are statistical quantities, the same numerical values of flame temperature, low limit excess air, and so forth, can be expected to apply to coal—air mixtures and to fuels derived from coal (see Fuels, synthetic). 

Fig. 4. Variation of adiabatic flame temperature with heat of combustion where + i+i°yk— CO- Note change of scale at 46.5 MJ /kg (20,000...

The insensitivity of adiabatic flame temperature to heat of combustion does not necessarily apply to the operational flame temperature, T, which is the flame temperature found in an actual furnace (remembering that this refers to some average temperature). The higher excess air requirements at higher C/H ratios coupled with greater thermal loads on longer flames generally results in markedly lower operational temperatures as the C/H ratio increases. 

Because this reaction is highly exothermic, the equiUbrium flame temperature for the adiabatic reaction with stoichiometric proportions of hydrogen and chlorine can reach temperatures up to 2490°C where the equiUbrium mixture contains 4.2% free chlorine by volume. This free hydrogen and chlorine is completely converted by rapidly cooling the reaction mixture to 200°C. Thus, by properly controlling the feed gas mixture, a burner gas containing over 99% HCl can be produced. The gas formed in the combustion chamber then flows through an absorber/cooler to produce 30—32% acid. The HCl produced by this process is known as burner acid. 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

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