Laminar counterflow mixing of acetylene into hot combustion products

Abstract

In an axisymmetric counterflow configuration, acetylene was blown against the hot post flame gases ofa rich premixed acetylene-air flame stabilized on a sinter metal, thereby creating a broad pyrolysis zone. This one-dimensional configuration has several interesting features for soot formation studies. Temperature, oxygen leakage through the premixed flame, and residence time in the pyrolysis region can be independently controlled by varying the stoichiometry and composition of the premixed flame and the velocity of the fuel counterflow. The thickness of the pyrolysis region, where the soot formation occurs, is large and, thus, experimentally well accessible and resolvable. Along the axis of symmetry, concentration profiles of various stable species up to C 4 hydrocarbons weremeasured by gas chromatography. Thermocouples were used for temperature measurements. The soot volume fraction was determined by a laser-light extinction method and Abel's inversion. The experimental results were compared with one-dimensional calculations using a kinetically based soot model. The reaction mechanism contains 62 species and about 400 reactions. The soot formation mechanism accounts for all possible coagulation processes between polyaromatic hydrocarbons (PAH) and soot particles, namely PAH-PAH coagulation leading to particle inception, PAH-particle coagulation, and particle-particle coagulation, for surface growth by C 2 H 2 addition and for oxidation. The results of the numerical simulation and the experiment show a good agreement for temperature and major species. The prediction for the maximum value of the soot volume fraction is quite good, but deviations in the measured and calculated profiles suggest an underestimated soot particle diffusion, indicating an overprediction of the particle sizes in the soot formation model.