Experimental Investigation of the Influence of Inert Gas on
                       Soot Formation

   Alexandre Flügel1,2, Sebastian Beer1, Stefan Will1, Johannes Kiefer2,3 and
                                Alfred Leipertz1,2
    1
     Lehrstuhl für Technische Thermodynamik (LTT), Universität Erlangen-Nürnberg, Am
                       Weichselgarten 8, D-91058 Erlangen, Germany
 2
  Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Str. 6,
                                D-91052 Erlangen, Germany
   3
     School of Engineering, University of Aberdeen, Fraser Nobel Building, King‘s College,
                             Aberdeen AB24 3UE, Scotland, UK

            (Alexandre Dias Flügel, alexandre.d.fluegel@ltt.uni-erlangen.de)



        The formation of soot in non-premixed flames is influenced by many
parameters, and the detailed mechanisms are yet to be fully understood. Adding inert
gas to the fuel supply of a burner has an inhibitory effect on soot formation. This
reduction in soot inception is probably caused by the reduction of the flame
temperature and hindered air entrainment due to a modified diffusion.
        In this work, laser-induced incandescence (LII) was employed in laminar
propane diffusion flames at atmospheric pressure in order to study the influence of
adding inert gas on soot concentration and primary particle size. A co-axial burner
stabilized with an air co-flow was used to produce a stable propane flame with
constant propane mass flow. The burner has a inner diameter of 13 mm, the inner
diameter of the co-flow was 89 mm, resulting in Re fuel=52 (for undiluted conditions)
and Reair = 102, respectively. The fuel was diluted with nitrogen, carbon dioxide and
argon. The mass flow rate of propane was kept constant at 4.3 mg/s and the inert
gas was varied from 0 to 5 mg/s in steps of 0.5 mg/s at 1 bar and 293 K. The fuel and
inert gas were premixed in a T-mixer. The mixture reached the combustion zone with
a laminar flow and homogeneous mixture. Laser-induced incandescence was
generated by a frequency-doubled pulsed Nd:YAG laser and detected with a
photomultiplier tube to obtain time-resolved LII signals. Adding 0.5 mg/s of Ar
reduced the soot volume concentration to 93% of the original value, in the cases of
N2 and CO2 the reduced values amounted to approximately 81%. Additional
increments of inert gas in further steps of 0.5 mg/s resulted in the same tendency .
        In consideration of primary particle sizes, nitrogen addition resulted in a
considerable initial effect, while particle size in the case of carbon dioxide only
changed significantly on the addition of larger flow rates.




             5th international workshop on Laser-Induced Incandescence
              May 9-11, 2012, Palais des Congrès, Le Touquet, France