China
Africa
Explore chapters and articles related to this topic
Thermodynamics of Combustion
Published in Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong, Combustion Engineering, 2022
Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong
Flames are discussed in detail in Chapter 5, but in this section we calculate the temperature rise across a flame. A flame is a rapid exothermic reaction zone that occurs at constant pressure, and the kinetic energy of the gases is insignificant. Hence, the adiabatic flame temperature can be obtained from Equation (3.68). For stoichiometric and lean mixtures at temperatures below 1900 K, dissociation is low enough so that the flame temperature may be calculated by assuming that combustion products go to completion. In this case, the mole fraction of each species is known from the complete reaction. The adiabatic flame temperature is obtained by equating the enthalpy of the reactants to the enthalpy of the products. The enthalpy of the reactants is known, and, by trial and error, the temperature can be determined that makes the enthalpy of the products equal to the enthalpy of the reactants. The procedure is shown in the following examples. For complex fuels, the heat of formation is first calculated from the heating value, as shown in Example 3.9. Adiabatic flame temperatures for various representative fuels are shown in Table 3.2.
Chemically Reacting Flows
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
The adiabatic flame temperature, Tad, refers to the highest temperature that will be obtained by burning a fuel under a specified set of conditions. This temperature is obtained when the reactants enter a well-insulated mixing chamber and the products of combustion leave the chamber at Tad. Thus all heat generated by the combustion reaction is transferred to thermal energy of the combustion products. The adiabatic flame temperature is normally around 2,300 K for several hydrocarbon fuels. It varies with the air–fuel ratio, AF, and excess air, EA. The adiabatic flame temperature decreases if more excess air is used since more thermal energy is required to raise the temperature of the nonreacting air. Conversely, if less air than the stoichiometric amount is supplied, Tad decreases due to incomplete combustion. Thus the maximum adiabatic flame temperature is reached at the air–fuel ratio corresponding to the stoichiometric amount of air.
Physical Foundation of Interior Ballistics
Published in Donald E. Carlucci, Sidney S. Jacobson, Ballistics, 2018
Donald E. Carlucci, Sidney S. Jacobson
One important parameter in determining the amount of energy transferred to the projectile is the temperature of the product gases. As you can see from our example, an increase in the temperature of the product gases will result in a decrease in the projectile velocity because Hp goes up. Typically, we can assume the product gases exit at a temperature between 0.6T0 and 0.7T0, where T0 is the adiabatic flame temperature of the product gases [7]. The adiabatic flame temperature of a gas is the temperature that is achieved if the gases burn to completion in the absence of any heat transfer or work being performed [1]. The calculation of the adiabatic flame temperature is relatively straightforward but requires iteration. This is beyond the scope of this chapter, but the reader is referred to the references at the end of this chapter for a complete description of the procedure. In addition, there are several commercially available codes (including some that come with the purchase of textbooks now, for instance, the book by Cengel and Boles [13]). To achieve our objectives, the temperature of the reaction products will always be given.
Analysis of a Pseudo-active Approach for the Control of Thermoacoustic Instabilities
Published in Combustion Science and Technology, 2022
Ennio Luciano, Jesús Oliva, Álvaro Sobrino, Javier Ballester
where represents the heat fluctuation released per unit of volume (also considered harmonic in time), the flame volume and the specific heat capacities ratio. Assuming that the flame is acoustically compact, can be considered constant over the flame volume and the integral can be approximated as shown in the right hand side of Eq. (2). The source term can be estimated for the different tests from the values of and measured with the microphones and photomultiplier. The thermodynamic parameters are calculated for the combustion products at the adiabatic flame temperature. Equation (2) was applied with the values measured for the different tests, yielding estimated values of below 10 W. Since these values are of the order of magnitude of the acoustic losses at the orifice ( could reach 10% of ) and the existence of other energy sinks (dissipation, loss through the boundaries), the effect of the injector is not negligible but may play a significant role in the acoustic balance in the combustion chamber, so modifying the limit cycle amplitude.
Numerical Study on the Combustion Process of n-heptane Spray Flame in Methane Environment Using Large Eddy Simulation
Published in Combustion Science and Technology, 2021
Wanhui Zhao, Lei Zhou, Zongkuan Liu, Jiayue Qi, Zhen Lu, Haiqiao Wei, Gequn Shu
where MWC, MWH, and MWα are the molecular weights of carbon atoms, hydrogen atoms, and species α respectively. nC,α and nH,α are the number of C and H atoms. Yα is the mass fraction of species α. Significant differences in the ignition process can be seen in Figure 7. Note that by adding more methane in the ambient gas, the oxygen concentration is slightly reduced. As a result, the value of the stoichiometric mixture fraction (Zst) is slightly reduced (Azimov, Kim, Bae 2010). When there is no CH4 in the initial ambient gas, the heat is released at both fuel-lean and fuel-rich regions before the ID. Once high-temperature kernels appear, the maximum temperature increases very quickly. At later times, the maximum temperature remains almost constant when the high-temperature zones move upstream toward the fuel-rich regions. At a higher CH4 concentration, ignition moves from fuel-richer to fuel less rich regions and the combustion temperature reaches the peak value at 0.3 ms after the ID. After that, the maximum temperature increases slightly owing to the oxidation of CH4. Meanwhile, the temperature of fuel-rich cells increases gradually, indicating that the combustion regions move upstream toward the fuel-rich regions. The basic flame structures in T-Z space can be evaluated at the instant of 0.3 ms after the ID. Reactions in fuel/air mixture are initiated at a low temperature for n-heptane flame due to evaporation. The decrease in the temperature leads to the reduction in the adiabatic flame temperature (not shown here). And the combustion of methane is not influenced by evaporation. The maximum combustion temperature is very close to the adiabatic flame temperature.
A Methodological Approach to Select a Suitable Azodicarbonamide Based Airbag Gas Generant
Published in Combustion Science and Technology, 2023
Jeyabalaganesh G, Sivapirakasam S P, Sreejith Mohan, Aravind S.L, Harisivasri Phanindra K
Adiabatic flame temperature is the theoretical maximum temperature that can occur during a chemical reaction. An airbag inflation reaction can be approximated to occur under adiabatic conditions, where the enthalpy of reactant formation equals the enthalpy of product formation. Based on this assumption, the adiabatic flame temperature (T) of the gas generant mixture can be computed using the equation,