A self-recirculation type low NO_x burner, in which a fresh air is injected through a nozzle with a high velocity speed and a hot burned gas is involved into the air stream through a recirculation space, has been experimentally investigated. The flowfield has been determined with a PIV system and spatial distributions of NO_x, temperature, CO and O_2 have also been determined in a test furnace. Results show that a recirculation of a burned gas is indeed induced outside the air nozzle and the NO_x level is significantly reduced. In the present burner, the amount of a recirculating burned gas attains 50% the fresh air and the NO_x level is decreased below 20ppm. Further measurements indicate that a recirculating flow is also induced inside the air nozzle and combustion is stabilized around a stagnant region of this recirculation flow. With an increase in the air flow this inner recirculation zone expands and its centre approaches the fuel nozzle. The evaporation of liquid fuel is promoted, resulting in formation of blue flame. The NO_x level is further reduced to 18ppm for the air excess ratio of 1.6 in the present burner system.
