Technical Report 136, c4e-Preprint Series, Cambridge

Numerical simulation of the evolution of soot precursor particles in a laminar ethylene diffusion flame

ref: Technical Report 136, c4e-Preprint Series, Cambridge

Associated Theme: Nanoparticles

Abstract

A detailed population balance model is used to investigate the physical and chemical evolution of nascent soot particles and their subsequent transformation to carbonaceous aggregates along the centerline of a laminar ethylene co-flow diffusion flame. The model incorporates the aggregate structure of particles and includes detailed compositional knowledge of the individual primary particles that constitute an aggregate. It thereby extends the range of comparisons that can be made with experimental measurements. The carbonisation process is studied using transmission electron microscope-like projections of aggregates and computed C/H ratio and fringe length distributions of the polycyclic aromatic hydrocarbons (PAHs) within the aggregates. Computed CxHy (x = 10 to 42 and y = 8 to 16) structures within particles are compared to the most thermodynamically stable aromatics (stabilomers) and a good correspondence is found. The overall model predicts the formation of aggregates between heights of 35 and 45 mm above burner where there is a rapid increase in both the number and diameter of primary particles in each aggregate, and a corresponding increase in the C/H ratio as a result of dehydrogenation reactions. The computed mode of the fringe length distribution shifts towards larger values with particle age. While some of the comparisons between numerical simulations and experimental data is satisfactory, the results of this study shows that further work is required to improve the soot chemistry model, particularly the oxidation rates on different surface site types.

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