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Fire dynamics
Published in Andrew Buchanan, Birgit Östman, Fire Safe Use of Wood in Buildings, 2023
Colleen Wade, Christian Dagenais, Michael Klippel, Esko Mikkola, Norman Werther
Char development also leads to cracks and fissures being formed that in turn greatly affect the heat and mass transfer between the solid and flame. The combustible volatiles that are released from the heat-exposed surface can mix with the surrounding air/oxygen and burn with a luminous flame. Where flame is not present over the exposed surface, oxygen may diffuse to the surface leading to char oxidation. The exposed surface recedes as combustion progresses due to the char contraction and possible char oxidation (Janssens and Douglas, 2004). Figure 3.2 from Law and Hadden (2020) illustrates where the various thermal decomposition processes occur in terms of the residual mass of the wood as a function of temperature for a piece of wood heated isothermally in an oxygen-rich environment.
Combustion Systems
Published in Charles E. Baukal, Industrial Combustion Pollution and Control, 2003
The fuel choice has an important influence on the pollution from a flame [4]. In general, solid fuels, such as coal and liquid fuels, like oil produce very luminous flames (see Fig. 3.6) which contain soot particles that radiate like black bodies to the heat load. Gaseous fuels like natural gas often produce nonluminous flames (see Fig. 3.7) because they burn so cleanly and completely without producing soot particles. A fuel like hydrogen is completely nonluminous as there is no carbon available to produce soot. Heavier hydrocarbon gaseous fuels like propane generally produce more luminous flames (see Fig. 3.8) than those of lighter hydrocarbon fuels like methane. In cases where highly radiant flames are required, a luminous flame is preferred. In cases where convection heat transfer is required, a nonluminous flame may be preferred in order to minimize the possibility of contaminating the heat load
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
The actual flame temperature is lower than the adiabatic equilibrium flame temperature due to imperfect combustion and radiation from the flame. The actual flame temperature is determined by how well the flame radiates its heat and how well the combustion system, including the load and the refractory walls, absorbs that radiation. A highly luminous flame generally has a lower flame temperature than a highly nonluminous flame. The actual flame temperature will also be lower when the load and the walls are more radiatively absorptive. This occurs when the load and walls are at lower temperatures and have higher radiant absorptivities. These effects are discussed in more detail in Baukal [2000].
The Investigation of Soot Free Length of Jet Flame of Propane and Carbon Dioxide Gas Mixture
Published in Combustion Science and Technology, 2022
Yuling Dou, Changfa Tao, Jingwu Wang, Huaqiang Chu, Yang Hua, Xiaoyong Liu
The turbulent jet flame can be divided into two parts according to the flame color, which is proved to be affected by the soot formation process (Zhang et al. 2017). The length of blue flame is called soot free length (without soot contain), and the yellow flame is called the luminous flame (with soot formation) (Sobiesiak and Wenzell 2005). Moreover, the total flame length () is expressed as the sum of soot free length () and the luminous flame length. The main reason for the difference of flame colors is soot emissions. The blue flame is generally considered to be caused by the radiation of water vapor and CO2, and the yellow flame is considered to be caused by the radiation of water vapor, CO2 and soot. In order to quantify the degree of soot reduction during the flame combustion process, the soot free length fraction () has been proposed which is defined as the ratio of to (Kumar and Mishra 2008; Sobiesiak and Wenzell 2005).