Optical background emission and structure in fuel/air flames seeded with diethyl sulfide, (C2H5)2S

The future need of safe disposal of chemical warfare agents and the increasing use of sulfur rich fuels make a quantitative understanding of the chemical reactions of similar containing compounds and their monitoring necessary. This report describes observations of the spectral emissions from the combustion of two different diffusion flames in a Seshadri type counterflow burner. These CH 4 /air and H 2 /air diffusion flames show almost identical flame structures in filtered CID camera and unfiltered color film pictures. Both display techniques show a single flame structure which is brightest in the near infrared. This structure exists as a thin band on the air inlet side of the burner close to the stagnation region. The location and spectral dependence of this radiation suggests spontaneous emission from vibration/rotation bands of the OH, e.g. the (3,0) lines centered at 950 nm and (4,0) lines at 730 nm. To explore the effects of sulfur containing hydrocarbons on the flame, (C 2 H 5 ) 2 S was added to the inlet air stream. The sulfur containing flames (with both CH 4 and H 2 as fuel) show the same emission bands as the unseeded flames with significant increases in spectral emission with increasing concentration of (C 2 H 5 ) 2 S in the oxidizer. As the mole fraction of (C 2 H 5 ) 2 S in air is increased from 0.3% to 2.0%, four new spectral bands successively appear, progressing from the stagnation region to the air inlet. Each of these thin bands radiates in the blue, i.e. wavelengths shorter than 500 nm. A single thin band close to the stagnation region increases with the (C 2 H 5 ) 2 S mole fraction and may be due to SH or SH 2 emissions. Radiation from the other three thin layers (about 1.5, 2.0 and 2.5 mm on the air inlet side) all increase with increasing (C 2 H 5 ) 2 S concentration. Consequently, they may be typical sulfur combustion products, such as CS, CS 2 or SO 2 . At selected (C 2 H 5 ) 2 S concentrations, a bright red band appears, possibly S 2 emission.