The influence of hydrogen and methane on the growth of carbon particles during acetylene pyrolysis in a burnt-gas flow reactor

Abstract The growth of carbon particles was studied in heated flows of a burnt-gas flow reactor containing mixtures of N 2 /C 2 H 2 , and N 2 /C 2 H 2 with addition of H 2 or CH 4 surrounded by a rich C 2 H 4 /air flame. Soot particle sizes and volume fractions were measured by laser-induced incandescence (LII) between 50 and 130 mm above the nozzle exit. The measurements indicate a soot-inhibiting effect of adding H 2 to the C 2 H 2 /N 2 flow on both, particle sizes and soot volume fractions. The effect of CH 4 addition to the C 2 H 2 /N 2 flows was ambivalent, depending on the methane-to-acetylene ratio. At gas mixtures with N 2 :CH 4 :C 2 H 2  = 0.42:0.35:0.23 and 0.39:0.32:0.29 by volume at fixed total flow rates, the measured soot volume fractions were substantially increased in presence of CH 4 , while the mean diameters of the particles were slightly decreased. Gas temperatures were measured by a generalized line-reversal method with Abel transformation. Temperatures of the surrounding C 2 H 4 /air flame were around 1600 K, and temperatures of the inner flows, where soot formation was measured, were between 1550 and 1630 K. Plug-flow reactor calculations provided a qualitative understanding of the influence of CH 4 on the soot particle growth.