Research On Low NO_X Emission Characteristics In Flameless Combustion

Flameless combustion has many advantages such as high combustion efficiency, uniform temperature distribution and lower NOx emission. As a new combustion technology, it has been extensively noticed by the industry and science field. The research is of momentous theoretical and practical significance for further development and application of flameless combustion.In this article, numerical simulation is used to study the flameless combustion and NOx emission characteristics. First of all, the conception of kinds of simulation model is illustrated and proved by the experimental data, κ-εturbulent model, discrete coordinate radiation model, PDF combustion model, thermal and prompt NOx formation model are selected.Secondly, the flameless combustion with different nozzle structure has been simulated. The results indicate that the burner with more air nozzles has better combustion characteristic, but too many can decrease the back flow of the high temperature exhausted air; rectangle nozzle with longer side in the radial direction can reduced NOx emission effectively; longer distance of nozzle can increase the average temperature in the furnace and reduce the peak temperature. Smaller obliquity angle of air jet can achieve uniform temperature distribution; unsympathetic air nozzle can enhance the back flow of the exhausted air and realize a better flameless combustion.Last, influences of jet stream parameters has been investigated. The result indicate that lower air excess ratio can reduce the oxygen concentration in the combustion region; the increase of oxygen concentration can increase the peak temperature,so the oxygen concentration should less than15%to reduce the NOx emission; lower velocity ratio can enhance the back flow of the exhausted air and obtain low oxygen condition; higher initial air temperature can increase the average temperature, NOx emission will rapidly increase when initial air temperature is higher than1300K; the peak temperature and NOx emission increased as the hydrogen concentration in fuel increased.