Flame propagation of gas combustion of industrial boiler burner
Flame propagation of gas combustion
1. How the flame spreads
There are three forms of flame propagation: normal flame propagation, explosion and deflagration.
The combustion process of gas in industrial and civil combustion equipment belongs to the normal flame propagation process, and the flame propagation in turbulent flow state is common in engineering.
When a partially combustible mixture is ignited, a very thin burning surface is formed at the fire site. This layer of flame surface burns and releases a large amount of heat, which heats the adjacent combustible gas mixture to increase its temperature. When it reaches the ignition temperature, it starts to ignite to form a new flame surface. In this way, the flame surface continuously moves towards the unburned gas, so that each layer of gas undergoes the process of heating, igniting and burning successively, thereby extending the combustion to the entire mixed gas. This phenomenon is called (normal) flame spread.
2. Flame propagation speed S
The propagation speed of the flame in the static or laminar combustible gas mixture in the tube is related to the heat dissipation of the gas flow to the tube wall. The larger the pipe diameter, the smaller the effect of the heat dissipation of the pipe wall on the flame propagation speed, and the greater the flame propagation speed.
When the pipe diameter is large to a certain extent, it can be approximately considered that the heat dissipation effect disappears, and the flame propagation speed approaches a maximum value, which is called the normal flame propagation speed S,
The physical meaning of the normal flame propagation velocity is the volume of the combustible mixture burned on the unit flame area per unit time, sometimes also called the burning velocity.
At a certain temperature and pressure, the normal flame propagation velocity S is determined by the physical and chemical properties of the combustible mixture, and it is a physical and chemical constant.
In a static medium or laminar airflow, the S of a flammable mixture is very small, generally several centimeters per second. Even for hydrogen with the largest S, its value is only a few meters per second.