Numerical Investigation on the Effect of Fuel Injection Timing on Soot Particle Size and Number Characteristics of Diesel Engine

Diesel engines are lucrative in terms of high thermal efficiency and low specific fuel consumption. The major drawbacks of these engines are high NOx and particulate matter (PM) emissions due to heterogeneous combustion. In the current emissions norms (BS-VI), a limit for particle number concentration is also introduced. There are few numerical studies investigating the soot particle size and number characteristics at different engine operating conditions. In this work, a parametric numerical study is conducted to investigate the effect of engine operating parameters on PM characteristics such as number density, size, and volume fraction. Simulations were performed using the Reynolds Averaged Navier Stokes equation with renormalization group K-ε turbulence model available in ANSYS FORTE CFD software. A detailed reaction mechanism consisting of 243 species and 1765 reactions with 66.8/33.3 weight percent of n-decane / alpha methyl napthalene diesel surrogate is employed to simulate diesel combustion and emissions. Method of the moment has been employed for predicting soot particle number and size for closed cycle simulations in ANSYS FORTE CFD software. Results indicate that an advanced injection timing reduces the peak particle number density and mean PM average diameter due to reduced soot formation rates and increased oxidation rates. An increase in injected fuel mass enhances the particle number density, mean PM average diameter and PM volume fraction due to surface growth and polycyclic aromatic hydrocarbons (PAH) coagulation reactions in the presence of high acetylene concentration and pyrene. Additionally, results indicate that the formation of polyaromatic hydrocarbon species decreased with an increase in engine speed, thereby decreasing the PM number density, mean PM average diameter and PM volume fraction.