Effect of Fuel-Air Mixing on Thermal NOx Formation

Abstract

This study was carried out to evaluate the effect of fuel-air mixing in the combustion chamber, using the small scale propane firing combustor being similar to the actual pre-combustion chamber type furnace.Mixing pattern in the combustion chamber was changed mainly by the variation of the velocity of fuel jet according to adjusting the width of nozzle slit of burner.The following conclusions can bereached.1) NOx, formation is greatly influenced by fuel-air mixing patterns in the combustion chamber.At certain mixing condition NOx formation reaches to the maximum level and getting better of worse of mixing condition causes to NOx reduction. In the bad mixing condition, heat release from the combustion zone increases and combustion temperature decreases, resulting NOx reduction. Meanwhile, in the good, decreasing of residence time and O2 concentration reduction in the high temperature region due to short flame zone causes low NOx level.2) The momentum ratio of fuel jet and air stream is considered to be the identifying factor of mixing pattern in the combustion chamber, and can be introduced to determine the qualitative relation between NOx formation and mixing pattern.3) Maximum NOx formation level appeared at certain volume ratio of fuel and air in the actual combustion zone, and this fuel-air ratio is considered to be the important factor to dominate the over all NOx formation level.