Insight of soot nanostructure and oxidation behavior in ammonia / ethylene coaxial diffusion flame

•Ammonia doping compressed the soot evolution area and delayed the formation stage.•Ammonia doping inhibits the formation and even agglomeration of soot particles.•Ammonia doping makes the soot particle nanostructure more disordered, easy to oxidation.•The chemical effect of ammonia on nanostructure of soot is significantly enhanced with doping ratio.