On the Propagation Process of Flame
On the Propagation Process of Flame
The combustion process of gaseous fuel is essentially the process of flame spreading in it. If the combustible mixture ignites in a certain part due to an electric spark or some hot object, forming a thin flame surface, the heat generated by the flame surface will heat the adjacent cooler mixture layer, causing its temperature to rise and ignite. This phenomenon is called flame propagation. The propagation speed depends on the physical and chemical properties of the premixed gas and the flow condition of the gas flow.
The experiment confirmed that the chemical reaction was only carried out in this thin layer of flame, which separated the unburned gas from the burned gas. Therefore, the characteristic of flame propagation is not that the combustion chemical reaction occurs simultaneously in the whole mixture, but that it is concentrated in the flame surface and carried out layer by layer.
According to the airflow conditions, the flame propagation in the premixed air flow can be divided into laminar flame propagation (or laminar combustion) and turbulent flame propagation (or turbulent combustion).
The discussion of the generation, development and propagation conditions of the flame propagation phenomenon and the factors affecting the propagation speed will help strengthen and control the combustion process in the industry, and thus establish a correct concept of the combustion process.
Although in actual combustion devices (such as combustion chambers of thermal engines and various kilns), the flame propagates in the micro-fluid gas, the flame propagation speed in laminar flow is the basic physical and chemical characteristics of combustible premixed gas, and is closely related to the flame propagation speed in turbulence, which is the basis for understanding the flame propagation in turbulence, and also the basis for further understanding the mechanism of the combustion process, Therefore, it is necessary to discuss the propagation of flame in laminar flow first.