Methane flame propagation in catalytically supported thermal combustion systems
Creators: name: Chen, Junjie
Publisher: name: figshare
Year: 2022
Subjects: subject: 90403 Chemical Engineering Design
subject: FOS: Chemical engineering
subject: 90499 Chemical Engineering not elsewhere classified
subject: 90402 Catalytic Process Engineering
subject: 91501 Computational Fluid Dynamics
subject: FOS: Other engineering and technologies
subject: 91502 Computational Heat Transfer
subject: 91505 Heat and Mass Transfer Operations

description: A flame is a rapidly reacting body of gas, commonly a mixture of air and a combustible gas, that gives off heat and, usually, light and is self-propagating. Flame propagation is explained by two theories: heat conduction and diffusion. In heat conduction, heat flows from the flame front, the area in a flame in which combustion occurs, to the inner cone, the area containing the unburned mixture of fuel and air. When the unburned mixture is heated to its ignition temperature, it combusts in the flame front, and heat from that reaction again flows to the inner cone, thus creating a cycle of self-propagation. In diffusion, a similar cycle begins when reactive molecules produced in the flame front diffuse into the inner cone and ignite the mixture. A mixture can support a flame only above some minimum and below some maximum percentage of fuel gas. These percentages are called the lower and upper limits of inflammability. Mixtures of natural gas and air, for example, will not propagate flame if the proportion of gas is less than about 4 percent or more than about 15 percent. It is necessary to first mix fuel and air to prepare a mixture with the desired adiabatic flame temperature. Frequently, in mixing the fuel and air, mixtures are created which are within the flammability limits. Such flammable mixtures are easily ignited and may burn at temperatures in excess of 2500 degrees Celsius. This would produce unwanted nitrogen oxides. Combustion or detonation of the flammable mixture can be avoided by maintaining the velocity of the fuel-air mixture above its maximum flame propagation velocity, which can be achieved by means known. Such velocity will prevent the development of combustion temperatures materially above 2000 degrees Celsius as might occur upon flashback of combustion from the catalyst to the fuel rich region where the fuel is introduced. Preferably, the fuel-air mixture is above this maximum flame propagating velocity at the inlet to the initial combustion catalyst surface. It is to be understood that specific operations will generally define the maximum flame velocity which is controlled by various conditions of operations, such as amount of air and fuel present, the type of fuel employed, temperature, and pressure. Suitable gas velocities which are above the actual maximum linear velocity for flame propagation, are generally above about 0.8 meters per second. Contributor: Junjie Chen, ORCID: 0000-0001-5055-4309, E-mail address: komcjj@gmail.com, Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China