Soot Emission from a Direct Injection Diesel Engine 2004-01-0927
This study analyzes the mass, number density and size of the soot formed and oxidized inside a direct injection diesel engine. The predictions were made using the modified KIVA-3V code with the Foster soot model for the different engine operating variables. The multi-step reactions in the Foster model were converted into a system of ordinary differential equations, which was solved using the VODE ODE solver. The computed soot emissions were well compared with the engine-out data obtained from experiments.
The change of the soot size during the expansion stroke was investigated. The surface growth, coagulation and oxidation of soot particles continuously changed size distribution. The sizes of soot particles at EVO timing were predicted to range from 1 nm to 50 nm.
Retarded SOI timing increased the portion of diffusion combustion. Since the surface growth was enhanced by the increase of the diffusion combustion and the oxygen was locally insufficient to oxidize the formed soot, the mass and size of soot at EVO timing were increased for the retarded SOI timing.
When air/fuel ratio was increased, the formation of both precursor and acetylene was reduced due to the low cylinder temperature and less remaining unburned fuel. The mass and size of the soot particles were decreased at EVO timing for the high air/fuel ratio.