The Effects of Fuel Chemistry and Particle Maturity on Soot Formation

A criterion to define soot maturity, a theoretical modeling approach to simulate it, and its effects on the surface reactivity of soot primary particles in laminar premixed and diffusion flames are presented in the first two chapters. It is shown that the core-shell internal nanostructure of soot primary particles is a function of the overall soot Hydrogen to Carbon (H/C) ratio and can be used to distinguish nascent from mature soot primary particles. The importance of considering dehydrogenation to predict the H/C ratio and maturity of soot is illustrated. It is shown that the decay of soot surface reactivity with maturity, i.e. soot aging, is a strong function of the internal nanostructure of soot primary particles. The necessity of simulating soot maturity for comparison with experimental measurements is discussed. Structural effects of biodiesel in terms of unsaturation, i.e. C-C double bond, its position, and the presence of the ester moiety on soot formation are investigated in chapters four and five. It is shown that unsaturation increases soot formation by higher production of soot chemical growth species while more centrally located double bond increases soot formation by producing more soot nucleating species. However, the ester moiety decreases soot formation by reducing the concentration of soot chemical growth species such as acetylene. Several experimental techniques for measuring flame temperature, soot volume fraction, primary particle diameter, and aggregate structure are compared to each other in the last chapter. It is shown that Time Resolved Laser Induced Incandescence is the most reliable method to measure the volume fraction and the primary particle diameter of mature soot particles. The sensitivity of thermocouple measurements to radiation correction is analyzed and it is shown that for accurate temperature measurement with a thermocouple, it is essential to use a locally measured variable emissivity to estimate radiation cooling effects.Ph.D