Abstract
he focus of the present study is to obtain detailed knowledge of the soot formation and oxidation processes in laminar diffusion flames. The present work studies the effects of various flame properties on soot growth and oxidation, and how they affect a flame’s sooting behaviour. Numerically modelling of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure is performed. The numerical results are compared with experimental data to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends are investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The results of experimental and numerical modelling agree relatively well in terms of the levels of soot volume fraction. Both results show a decrease in soot loading as more ethanol is added in the fuel stream. The work continues by numerically studying the oxidation of soot in laminar ethylene/air coflow diffusion flames. A new model for soot oxidation, a complex process in numerical soot modelling, is developed based on the observation that soot ageing reduces surface reactivity. Using this new model, it is possible to capture the correct behaviour of both smoking and non- smoking flames in various flame configurations. Along with a detailed soot sectional model, the new model predicts the correct soot volume fractions, smoke emission characteristics, and primary particle diameters for different flames without any variation in model parameters. The work extends to study soot surface reactivity in the growth and oxidation regions. Laminar ethylene/air and methane/air coflow diffusion flames are numerically studied to develop a unique soot surface reactivity model. A newly developed surface character model simultaneously accounts for soot surface reactivity in surface growth and oxidation by considering soot ageing and its effects on the particle surface. The new model, which eliminates tuning of one modelling parameter, reconciles the quantification of the evolving soot surface character for both growth and oxidation. The model is shown to be uniquely capable of predicting soot concentrations and smoke emissions within experimental uncertainty in a wide range of laminar diffusion sooting flames.
Highlights
A great portion of all power generation and transportation energy comes from combustion
It is interesting to observe that the high soot concentrations occur in the flame centerline region, which is in contrast to laminar coflow diffusion flames of gaseous fuels with comparable peak soot volume fractions, where the peak soot volume fraction occurs in the flame wing, e.g., [5] [22]
The present work investigated the effects of adding ethanol to fuel on soot formation in gasoline/air coflow diffusion flames at atmospheric pressure experimentally and numerically
Summary
A great portion of all power generation and transportation energy comes from combustion. The continued development of quantitatively accurate soot particle formation models is of interest to both academia and industry Such models have the potential to increase our fundamental understanding of soot formation processes and provide tools for engineers to aid in their design of cleaner combustion devices. Numerical modelling of combustion-generated soot is very challenging since it involves complex processes including inception, condensation, surface growth, coagulation, oxidation, and fragmentation. Environmental and health issues lead combustion device designers to attempt to reduce combustion-generated soot emissions; this challenge requires a comprehensive understanding of the physics of combustion, especially that of soot formation, which is complex and remains poorly understood today. The effect of collision efficiency on soot formation is considered
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