Development Of Premixed Combustion Analysis Systems And The Effects Of Synthesis Conditions On The Soot Structure Properties

The reaction mechanism of soot formation has become one of the central themes of research activities in the area of combustion, mostly due to environmental and health concerns on pollutant emission from combustion devices. The need to provide a better physical and chemical understanding of soot formation in the high-pressure and high-temperature and inhomogeneous engine combustion chamber requires the development of combustion analysis systems and further fundamental combustion researches. Therefore, combustion analysis systems have been developed to conduct comprehensive experimental investigation of soot formation in premixed flames. The effects of temperature and fuel-air equivalence ratio on nanostructure, fractal dimension and size of soot have been investigated for laminar, atmospheric-pressure premixed methane flames. The major research work and results of this dissertation are listed as follows:1. Combustion system has been developed to investigate flame-formed soot in premixed laminar flames produced on a commercial McKenna burner, with precisely adjustable equivalence ratio and sampling height above burner. For precise temperature measurement of different flame locations, a high-temperature thermocouple temperature measurement system has also been designed.2. A thermophoretic sampling particle diagnostic (TSPD) system and an in-situ probe sampling system have been developed to obtain combustion products for physical and chemical investigation of soot formation. The TSPD system has been further developed on the basis of an advanced electric cylinder, with a freely positionable and accurate linear motor and very high dynamic response.3. Different sizes and morphology of soot are found depending upon the aging of soot formation. With the increase of height above burner, primary particle size increases from ~10nm to ~30nm, and the value of aggregate fractal dimension decreases. Fringe length extends and soot nanostructure becomes more ordered during the maturation process.4. With the increase of flame temperature, both of the primary particle size and aggregate fractal dimension value decrease, signifying that soot particles are more loosely clustered in higher temperature environment. It is revealed that both the fringe tortuosity and separation distance decrease as temperature increases, while the mean fringe length increases distinctly, indicating the soot evolution toward a more graphitic structure and higher resistance toward oxidation. 5. With the increase of fuel-air equivalence ratio, both of the primary particle size and the number of primary particles in aggregates increase. Aggregate fractal dimension value decreases, implying more soot particles with chain-like structure in higher fuel-air equivalence ratio environment. The mean fringe length increases, while the fringe tortuosity and separation distance decrease as fuel-air equivalence ratio increases, indicating the tendency of soot nanostructure toward a more ordered state.