Modeling and measurements of size distributionsin premixed ethylene and benzene flames

摘要

This study demonstrates the major differences in the evolution of the particle size distributions (PSDs),both measured and modeled, of soot in premixed benzene and ethylene flat flames. In the experiments, sootconcentration and PSDs were measured by using a scanning mobility particle sizer (SMPS, over the sizerange of 3–80 nm). The model employed calculations of gas phase species coupled with a discrete sectionalapproach for the gas-to-particle conversion. The model includes reaction pathways leading to the formationof nano-sized particles and their coagulation to larger soot particles. The particle size distribution,both experimental and modeled, evolved from a single particle mode (the nucleation mode) to a bimodalsize distribution. An important distinction between the results for the ethylene and benzene flames is thebehavior of the nucleation mode which persists at all heights above the burner (HAB) for ethylene whereasit was greatly suppressed at greater HAB for the benzene flames. The explanation for the decreased nucleationmode at higher elevations in the benzene flame is that the aromatics are consumed in the oxidationzone of the flame. Fair predictions of particle-phase concentrations and particle sizes in the two flames wereobtained with no adjustments to the kinetic scheme. In agreement with experimental data, the model predictsa higher formation of particulate in the benzene flame as compared with the ethylene flame.