Carbon particle size distribution function calculations in 3D CFD Diesel engine simulations

A model to calculate the carbon particle size distribution function in multidimensional CFD simulations of combustion in diesel engine has been implemented in a parallel version of the KIVA3V code, modified to adopt detailed reaction kinetics. The present paper presents an approach in following the evolution of the particles fully coupled with the main oxidation and pyrolysis of the fuel in a 3D CFD framework. The coupling between gas-phase and carbonaceous particles accounts for the role of benzene and polycyclic aromatic hydrocarbons in nucleation and surface growth processes. According to the adopted approach, the size distribution function is discretized into a finite number of classes of fixed molecular weight. As a result, not only integral quantities like the total mass and number of particles can be calculated, but also the shape of the particles size distribution function. To this aim, pure n-Heptane was chosen as reference fuel both in experiments and computations. The n-heptane reaction scheme has been extended, to include PAH kinetics, thus the complete reaction scheme comprises 132 chemical species and 2206 reaction steps. A single-cylinder diesel engine was run with n-heptane to collect data for numerical comparison, thanks to the n-heptane's similarity in cetane number with conventional diesel fuel. The engine has the same architecture of the four-cylinder FIAT 1.9 Multi-Jet engine. Computed particle size distribution functions have been compared to particles differential mobility measurements at the engine exhaust, performed by the CAMBUSTION DMS 500. The qualitative analysis of the preliminary results has given a reasonable picture of the general development of the particles formation phenomenon and the feasibility of a sectional model implementation in engine simulations has been assessed, although the model exhibits the tendency to overestimate the number of particles within the range 5-160 nm.