A Study of Radiant Tube Flame Structure and NO_x Emissions

ABSTRACT

The structure and NO_x behavior of turbulent natural gas/air flames, confined in a quartz radiant tube, are experimentally studied. The configuration features initially unmixed reactants with fuel admitted through multiple holes and air admitted through mild swirl slots. Visible flame heights and colors demonstrate that two burning modes exist, one involving long, orange flames and another involving short, blue flames. Near-injector species concentrations and exhaust NO_x measurements indicate that the short, blue flames exhibit varying degrees of fuel/air premising. Enhanced mixing is caused by factors including swirl, hot wall stabilization, and acoustic interactions. The present results are compared with those of several past studies to gain further insight into flame structure. Operation of radiant tubes in the long, orange burning mode with a slightly fuel-lean equivalence ratio yields relatively low NO_x emission index, more uniform wall temperature, higher heat transfer efficiency, and less audible noise than the short, blue mode.

Key Words:

• Turbulent diffusion flames
• oxides of nitrogen
• confined flames
• natural gas burners

Additional information

Notes on contributors

L. G. BLEVINS

Corresponding author. Linda Blevins, 1003 Chaffee Hall, Purdue University, W. Lafayette, IN 47907-1003.