Time-resolved laser-induced incandescence for particle sizing and laser light extinction for soot volume fraction was applied simultaneously to study the influence of methane addition on soot formation in acetylene pyrolysis. Three series of the experiments with initial mixtures of 2% C2H2+Ar, 1% CH4+Ar and 2% C2H2 + 0.5/1/2% CH4+Ar in the temperature range of 1600-2300 K and the pressure range of 4-5 bar behind reflected shock waves were carried out. The kinetic characteristic of the soot formation process the induction time of soot particle inception as well as the temperature dependences of final values of soot volume fraction and particle sizes have been determined and analyzed. An essential increase of soot volume fraction, particle sizes and a decrease of induction time of soot inception at methane addition to acetylene were observed. The gas phase kinetic modeling of the investigated processes up to the soot nuclei precursors formation has been performed. Analysis of gas kinetic stages of acetylene decomposition with methane addition has demonstrated the significant increase of the rates of pyrene formation followed by PAH growth due to effective propargyl C3H3 formation. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.