A completely premixed burner consists of a mixing device and a head. According to the different structures of the burner head, fully premixed burners can be divided into three types:
(1) There is a fire channel head structure:
(2) Head structure without fire channel:
(3) Head structure made of metal mesh or ceramic plate flame stabilizer.
Completely premixed combustion flame propagates very quickly, has poor flame stability, and is prone to flashback. In order to prevent backfire, the velocity field of the airflow must be made as uniform as possible to ensure that the airflow velocity at each point is greater than the flame propagation speed under the lowest load. Use small fire holes to increase the heat dissipation of the flame from the fire hole wall, thereby reducing the flame propagation speed. , is an effective measure to prevent tempering from occurring. Small flame hole burners are widely used in civilian burning appliances where the heat load is not very large. The small fire hole plate type fully premixed burner is not suitable for industrial burners with high thermal intensity. A large number of small fire holes will greatly increase the size of the burner head. Water cooling of the burner head can be used to enhance the heat dissipation of the flame, thereby reducing the flame propagation speed.
Completely premixed combustion, because a large amount of air is premixed before combustion, the outlet velocity of the premixed airflow is greatly increased. When the load is large, misfire may also occur. Industrial fully premixed burners often use a back-to-back fire channel to stabilize the flame.
When the uniformly mixed gas-air mixture enters the fire channel through the fire hole, due to the sudden expansion of the flow section, a high-temperature flue gas return zone is formed at the entrance of the fire channel. The recirculating flue gas not only heats the mixture, but also acts as a stable ignition source. The fire channel is made of refractory materials and is similar to an adiabatic combustion chamber, where combustible gas can reach high combustion temperatures. The high-temperature recirculation flue gas and the red hot fire channel wall both play a very good role in stabilizing the flame.