There is no clear international standard for the definition of flameless combustion state of burner. At present, the research of wunning father and son is more recognized by everyone. Through a large number of experiments, they have obtained the relationship between the internal circulation rate kV of flue gas and temperature when methane is mixed and burned simultaneously in the mode of diffusion combustion.

The axial evolution and radial diffusion of fuel jet MF and oxidant jet Ma will cause the entrainment of ambient air me, so that the central area of the jet is gradually diluted by combustion products (CO2 and H20) and non reactive gases (N2) to achieve "low oxygen" combustion conditions.

In addition, there are some other judgment methods. For example, the temperature rise is used to determine whether the combustion is in a flameless combustion state. Kumar et al. Believe that the combustion with the space temperature change of about 15% after the temperature rise in the reactor is normalized can be defined as flameless combustion. Antonio lavaliere et al. Used the inlet temperature and temperature rise to describe the combustion state, and obtained the following conclusions: the inlet temperature is lower than the spontaneous combustion temperature and the temperature rise is greater than the inlet temperature, which is called feedback combustion; When the inlet temperature is higher than the spontaneous combustion temperature and the temperature rise is higher than the inlet temperature, it is called high temperature combustion; When the inlet temperature is higher than the spontaneous combustion temperature and the temperature rise is lower than the inlet temperature, it is called flameless combustion.