What is the Basic Process of Fuel Combustion?
What is the Basic Process of Fuel Combustion?
The combustion of any fuel must meet sufficient conditions, that is, it must have a sufficient temperature to make the fuel reach its ignition point before it can start combustion; Second, there must be enough oxidant (usually air) to ensure normal combustion. That is to say, the normal combustion process of all combustible mixtures is composed of two stages: ignition and combustion itself, that is, they must be ignited before combustion.
Ignition: The so-called ignition refers to the process in that combustible materials start to burn and produce flame due to the accelerated chemical reaction of the material itself. (1) Spontaneous ignition causes the fuel to reach a certain temperature and pressure, and then it will ignite. The whole fuel will burn explosively at the same time. This phenomenon is called spontaneous ignition or self-ignition.
Flammable mixture contacts with an external high-temperature heat source and ignites, which is called “ignition”, also known as “forced ignition”.
The essence of ignition is to ignite part of the combustible mixture first and then transfer the combustion to the rest. It is unnecessary to heat the whole system during ignition, so it has important practical significance.
The difficulty of ignition is related to the temperature of the introduced heat source. The higher the temperature, the easier it is to ignite. When the heat source area is large, it can also be ignited at a lower temperature, but the temperature cannot be lower than the ignition temperature of the material. There are three methods of positive ignition: high-temperature solid ignition, high-temperature gas ignition, and spark discharge ignition.
The surface temperature required for ignition of the high-temperature solid is usually higher than the minimum ignition temperature of this fuel. The smaller the size of the source, the lower the temperature and pressure of the fuel, and the greater the flow rate, the higher the required surface temperature of the object. High-temperature gas ignition is a method to ignite fuel with the flame of the ignition burner. This method is more commonly used in industrial combustion devices.
Generally speaking, the most important factors to ignite fuel with ignition flame are flame temperature, fire size, and contact time.
Spark discharge ignition is to apply a voltage between the electrodes of the spark plug to discharge, and uses the energy of this discharge to carry out the point. It can be applied to most combustion devices. Sparks produced by spark discharge is caused by the thermal effect of spark energy. Heat conduction and diffusion of activated particles are carried out between the spark core and the surrounding mixed gas. If the unburned mixed gas layer close to the flame zone receives enough energy, the flame will spread and will soon transition to stable flame propagation.