Surface Ageing of Soot Particles

1
Surface Ageing of Soot Particles
R I A Patterson, J Singh M Kraft Department of
Chemical Engineering, University of Cambridge
Reactions on the surface of soot are the
principal route by which mass is transformed from
the gas to solid phase in laminar premixed
flames. However, the reactivity of soot
particles decreases significantly over time so an
accurate model is necessary to predict soot mass.

• The model we use consists of three main processes
• Particle inception when two pyrene molecules
  coagulate
• Coagulation two particles form a new sphere
  with the same total mass
• Surface events chemical reactions on the
  particle surface (4 types)

• Pyrene condensation
• C2H2 addition
• OH oxidation
• O2 oxidation

3 Active Sites Model
An important part of the model for the rate of
C2H2 addition and O2 oxidation is the number of
active sites on the surface of the soot particle
1,2. This is known to decrease over time but
little is known about the decay process except
that it never reaches 0 so we model the density
of active sites, a,on the surface of a particle
as an offset exponential decay process in the
particle age t
This exponential decay is calculated along with
the deferred processes. When two particles
coagulate the age of the new particle is
calculated from the surface areas a1, a2 and ages
t1, t2 of the old particles as
4 Decay constant

References
1 J Appel at al. Kinetic Modelling of soot
formation with detailed chemistry and physics
Laminar premixed flames of C2 hydrocarbons.
Combust. Flame 121 122-136 (2000) 2 M
Frenklach and H Wang in H Bockhorn (Ed), Soot
Formation in Combustion - Mechanisms and Models.
Springer Verlag, Berlin 1994, 165-192 3 R I A
Patterson et al. The Linear Process Deferment
Algorithm A new technique for solving population
balance equations. Technical Report 26,
c4e-Preprint Series, Cambridge, 2004