Discussion on the ignition point of combustion system
Usually, a combustible mixture system can still have a slow oxidation reaction at lower temperatures. If the heat generated by the reaction is greater than the heat diffused outward from the system, the system temperature will continuously rise and accelerate the reaction, leading to ignition and combustion. This ignition process is called thermal ignition. Under normal pressure, a combustible system needs to reach this energy condition and cause combustion at a certain temperature, which is the ignition temperature of the combustible material itself, also known as the ignition point. The ignition point is influenced by pressure and fuel composition, and varies depending on the shape, size, and material of the container used for measurement. Therefore, it is necessary to clarify these basic conditions. In gaseous fuels, the ignition point usually decreases with increasing pressure, and in addition to hydrogen and methane, there is also a slight tendency to decrease with increasing fuel concentration.
When it is below the ignition temperature, the heat dissipated by the combustible system is greater than the reaction heat, which will quickly cool down and prevent ignition and combustion. The theoretical ignition point is when the heat dissipated is equal to the heat released by the reaction, but in reality, it will not burn at this time. The actual ignition temperature is slightly lower than the temperature at which the heat dissipated is slightly lower than the reaction heat, but even at this time, most combustible mixtures need to stay for a period of time before they can ignite and burn. This period is a period of accelerated reaction from slow to intense, known as the induction period (incubation period). The length of the induction period is related to temperature, and the ignition temperature is usually the low temperature that can cause ignition. At this time, the induction period is long.