Detailed Kinetic Modeling and Laser Diagnostics of Soot Formation Process in Diesel Jet Flame

Abstract

This work investigates the soot formation process in diesel jet flame using a detailed kinetic soot model implemented into the KIVA-3V multidimensional CFD code and 2D imaging by use of time-resolved laser induced incandescence (Lll). The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver using Message Passing Interface (MPI). This allows for the chemical reactions to be simulated in parallel on multiple CPUs. The detailed soot model used is based on the method of moments, which begins with fuel pyrolysis, followed by the formation of polycyclic aromatic hydrocarbons, their growth and coagulation into spherical particles, and finally, surface growth and oxidation of the particles. The model can describe the spatial and temporal characteristics of soot formation processes such as soot precursors distributions, nucleation rate and surface reaction rate. The experiments by use of laser induced incandescence were conducted using a constant volume combustion vessel which simulated diesel engine conditions. The distribution of soot volume fraction and particle diameter in diesel jet was revealed by time-resolved Lll measurements, and qualitative agreement was obtained between the experimental and simulation results. The experimental results show that the smaller particles are made up of majority of soot formation region in the jet at the early time of the start of soot formation, which become larger around the periphery of the soot formation region with transition to the diffusion combustion phase, and rapidly transform the large particle after the end of injection. Also, simulation results show that the soot particles are formed to surround the soot precursor formation region and to extend downstream. It was also found that the dominant soot growth process differs by the region in the fuel jet. The particle inception is fast around the central region of the jet, and C 2 H 2 surface reaction rate becomes higher toward the periphery of the jet.