Probability Density Function (PDF) is often selected to couple chemistry with turbulencefor complex reactive flows since complex reactions can be treated without modelingassumptions. This paper describes an investigation into the use of the particlesapproximation of this transport equation approach applied to Homogeneous ChargeCompression Ignition (HCCI) combustion. The model used here is an IEM (Interaction byExchange with the Mean) model to describe the micromixing. Therefore, the fluid within thecombustion chamber is represented by a number of computational particles. Each particleevolves function of the rate of change due to the chemical reaction term and the mixingterm. The chemical reaction term is calculated using a reduced mechanism of n-heptaneoxidation with 25 species and 25 reactions developed previously. The parametric study witha variation of the number of particles from 50 up to 104 has been investigatedfor three initial distributions. The numerical experiments have shown that the hatdistribution is not appropriate and the normal and lognormal distributions give the sametrends. As expected when the number of particles increases for homogenous mixture (i.e.high turbulence intensity), the in-cylinder pressure evolution tends towards thehomogeneous curve. For both homogeneous and inhomogeneous (i.e. low turbulence intensity)cases, we have found that 200 particles are sufficient to model correctly the system, witha CPU time of a few minutes when a restriction of initial distribution is adopted.
