Numerical investigation of soot formation and oxidation under Diesel engine conditions
SAE Technical Paper, (1995)Abstract
Numerical simulations for an n -heptane fueled high pressure and high temperature chamber under Diesel engine conditions have been performed to study soot formation and oxidation processes. A kinetically based soot model has been applied, which accounts for the pyrolysis and oxidation of fuel and formation of polycyclic aromatic hydrocarbons (PAHs) by the use of a detailed kinetic mechanism. PAH growth and oxidation is modeled by a fast polymerization process, coagulation of PAHs leads to particle inception. The soot particles are allowed to coagulate with other particles and PAHs. The interaction of soot particles with the gas phase is modeled by heterogeneous surface reactions leading to particle growth due to acetylene addition and particle oxidation by hydroxyl radicals and molecular oxygen.
The conservation equations for the fluid dynamics are solved with the KIVA II code and the coupling with chemistry is treated by employing the flamelet concept. Instead of using flamelet libraries, we applied a new approach by solving the unsteady flamelets interactively with the CFD solver, to account for the flamelet's history concerning pressure, scalar dissipation rate and enthalpy. Each flamelet is representative for a certain domain of the investigated chamber with sufficiently homogeneous conditions.
A comparison of the calculations with experimental data for spray development, ignition delay, and spatially resolved soot concentrations shows good agreement. The influences of the chamber temperature, pressure, and injection pressure on soot concentrations are discussed, and the individual parts of the soot growth and oxidation contributions will be specified.