A novel nonintrusive soot diagnostics methodology was developed, validated and applied for in-situ determination of temperature, volume fraction and refractive index of soot aggregates formed inside flames by using near-infrared emission spectrometry. Research was conducted in three main parts, first one addressing development and validation of a comprehensive &quot / direct&quot / model for simulation of line-of-sight radiative emission from axisymmetric sooty flames by coupling sub-models for radiative transfer, radiative properties and optical constants. Radiative property estimation for soot agglomerates was investigated by experimentally validating discrete dipole approximation against microwave measurements and using it as reference to assess applicability of simpler Rayleigh-Debye-Gans approximation for fractal aggregates (RDG-FA). Comparisons between predictions of two methods for soot-like model aggregates demonstrated that radiative property predictions of RDG-FA are acceptably accurate for relatively small soot aggregates encountered in small-scale flames. Part two concerns experimental investigation of an axisymmetric ethylene/air diffusion flame by Fourier Transform Near-Infrared spectroscopy. Measurement of line-of-sight emission intensity spectra was performed along with analyses on calibration, noise, uncertainty and reproducibility. A noise characterization approach was introduced to account for spatial fluctuations which were found to dominate over spectral noise. Final part focuses on development, evaluation and application of an inversion methodology that inputs spectral emission intensity measurements from optically thin flames, removes noise, identifies soot refractive index from spectral gradients and retrieves soot temperature and volume fraction fields by tomographic reconstruction. Validation with simulated data and favorable application to measurements indicate that proposed methodology is a promising option for nonintrusive soot diagnostics in flames.

The first goal of this thesis is to develop and validate a modeling tool into which fundamental combustion chemistry and aerosol dynamics theory are implemented for investigating soot formation/oxidation in multi-dimensional laminar coflow diffusion flames taking into account soot polydispersity and fractal-like aggregate structure. The second goal is to use the tool to study soot aggregate formation/oxidation in experimentally studied laminar coflow diffusion flames to advance the understanding of soot aggregate formation/oxidation mechanism. The first part of the thesis deals with the large CPU time problem when detailed models are coupled together. Using the domain decomposition method, a high performance parallel flame code is successfully developed. An advanced sectional aerosol dynamics model which can model fractal-like aggregate structure is successfully implemented into the parallel flame code. The performance of the parallel code is demonstrated through its application to the modeling of soot formation/oxidation in a laminar coflow CH4/air diffusion flame. The parallel efficiency reaches as high as 83%. The second part of the thesis numerically explores soot aggregate formation in a laminar coflow C2H4/air diffusion flame using detailed PAH-based combustion chemistry and a PAH-based soot formation/oxidation model. Compared to the measured data, flame temperature, axial velocity, C2H2 and OH concentrations, soot volume fraction, the average diameter and the number density of primary particles are reasonably well predicted. However, it is very challenging to predict effectively the average degree of particle aggregation. To do so, particle-particle and fluid-particle interactions that may cause non-unitary soot coagulation efficiency need to be considered. The original coagulation model is enhanced in this thesis to accommodate soot coagulation efficiency. Different types of soot coagulation efficiency are numerically investigated. It is found that a simple adjustment of soot coagulation efficiency from 100% to 20% provides good predictions on soot aggregate structure as well as flame properties. In the third part of the thesis, the effects of oxidation-driven soot aggregate fragmentation on aggregate structure and soot oxidation rate are studied. Three fragmentation models with different fragmentation patterns are developed and implemented into the sectional aerosol dynamics model. The implementation of oxidation-driven aggregate fragmentation significantly improves the prediction of soot aggregate structure in the soot oxidation region.

The first goal of this thesis is to develop and validate a modeling tool into which fundamental combustion chemistry and aerosol dynamics theory are implemented for investigating soot formation/oxidation in multi-dimensional laminar coflow diffusion flames taking into account soot polydispersity and fractal-like aggregate structure. The second goal is to use the tool to study soot aggregate formation/oxidation in experimentally studied laminar coflow diffusion flames to advance the understanding of soot aggregate formation/oxidation mechanism. The first part of the thesis deals with the large CPU time problem when detailed models are coupled together. Using the domain decomposition method, a high performance parallel flame code is successfully developed. An advanced sectional aerosol dynamics model which can model fractal-like aggregate structure is successfully implemented into the parallel flame code. The performance of the parallel code is demonstrated through its application to the modeling of soot formation/oxidation in a laminar coflow CH4/air diffusion flame. The parallel efficiency reaches as high as 83%. The second part of the thesis numerically explores soot aggregate formation in a laminar coflow C2H4/air diffusion flame using detailed PAH-based combustion chemistry and a PAH-based soot formation/oxidation model. Compared to the measured data, flame temperature, axial velocity, C2H2 and OH concentrations, soot volume fraction, the average diameter and the number density of primary particles are reasonably well predicted. However, it is very challenging to predict effectively the average degree of particle aggregation. To do so, particle-particle and fluid-particle interactions that may cause non-unitary soot coagulation efficiency need to be considered. The original coagulation model is enhanced in this thesis to accommodate soot coagulation efficiency. Different types of soot coagulation efficiency are numerically investigated. It is found that a simple adjustment of soot coagulation efficiency from 100% to 20% provides good predictions on soot aggregate structure as well as flame properties. In the third part of the thesis, the effects of oxidation-driven soot aggregate fragmentation on aggregate structure and soot oxidation rate are studied. Three fragmentation models with different fragmentation patterns are developed and implemented into the sectional aerosol dynamics model. The implementation of oxidation-driven aggregate fragmentation significantly improves the prediction of soot aggregate structure in the soot oxidation region.

The current study represents the first application of commercial laser-induced incandescence (LII) instrumentation at the University of Toronto Combustion Research Laboratory, for the characterization of soot in atmospheric laminar co-flow diffusion flames. An experimental apparatus was designed to accommodate the optical diagnostic, and to provide the means to probe various regions of the flames. An experiment with a well-characterized non-smoking ethylene-air diffusion flame was carried out to validate the performance of the LII instrument. Three measurement heights were analyzed; those at 40, 50, and 60 mm above the fuel exit. The soot volume fraction results were found to be in good agreement with those from the literature. The highest value was found to be 8.3 ppm at a height of 40 mm. While the instrumentation could report primary particle diameters, it was determined from the validation trial that the results were still premature. Further work is needed to validate the results of the instrument, especially for the particle size data.

The gaseous species concentration of Jet A-1, GTL, CTL and a blend of 80 vol.% GTL and 20 vol.% hexanol jet fuels in laminar coflow diffusion flames have been measured and studied. These species are carbon monoxide, carbon dioxide, oxygen, methane, ethane, ethylene, propylene, and acetylene. Benzene and propyne concentrations were also detected in CTL flames. 1-Butene has been quantified for the blend of GTL and hexanol flame. The detailed experimental setup has been described and results from different flames are compared. The CO is produced in a same amount in all the flames. The CTL flame had the largest and GTL/hexanol flame had lowest CO2 concentrations. The results indicate that GTL and GTL hexanol blend flames produce similar concentrations for all the measured hydrocarbon species and have the highest concentration among all the jet fuels. The experimental results from Jet A-1 fuel are also compared with numerical studies by Saffaripour et al.

The gaseous species concentration of Jet A-1, GTL, CTL and a blend of 80 vol.% GTL and 20 vol.% hexanol jet fuels in laminar coflow diffusion flames have been measured and studied. These species are carbon monoxide, carbon dioxide, oxygen, methane, ethane, ethylene, propylene, and acetylene. Benzene and propyne concentrations were also detected in CTL flames. 1-Butene has been quantified for the blend of GTL and hexanol flame. The detailed experimental setup has been described and results from different flames are compared. The CO is produced in a same amount in all the flames. The CTL flame had the largest and GTL/hexanol flame had lowest CO2 concentrations. The results indicate that GTL and GTL hexanol blend flames produce similar concentrations for all the measured hydrocarbon species and have the highest concentration among all the jet fuels. The experimental results from Jet A-1 fuel are also compared with numerical studies by Saffaripour et al.

The current study represents the first application of commercial laser-induced incandescence (LII) instrumentation at the University of Toronto Combustion Research Laboratory, for the characterization of soot in atmospheric laminar co-flow diffusion flames. An experimental apparatus was designed to accommodate the optical diagnostic, and to provide the means to probe various regions of the flames. An experiment with a well-characterized non-smoking ethylene-air diffusion flame was carried out to validate the performance of the LII instrument. Three measurement heights were analyzed; those at 40, 50, and 60 mm above the fuel exit. The soot volume fraction results were found to be in good agreement with those from the literature. The highest value was found to be 8.3 ppm at a height of 40 mm. While the instrumentation could report primary particle diameters, it was determined from the validation trial that the results were still premature. Further work is needed to validate the results of the instrument, especially for the particle size data.

L'étude et la compréhension du comportement des flammes de diffusion sont nécessaires et ceci à cause de leur présence dans diverses applications industrielles. Dans la présente étude, cette flamme de diffusion laminaire est issue d'un jet circulaire de méthane et d'un jet coaxial d'air. Deux moyens sont proposés afin d'influencer cette flamme: l'application d'un champ magnétique non-homogène et l'enrichissement du jet d'air coaxial en oxygène. L'effet de ces deux facteurs est étudié au niveau des caractéristiques de la flamme hauteur de décrochage ou lift et la longueur de la flamme), son comportement, sa stabilité et les instabilités d'écoulement en amont de la flamme, de front de flamme et de sommet de la flamme (flickering). L'effet du champ magnétique dépend du signe de son gradient, et cet effet est dû à la génération d'une force magnétique et de la modification des courants de convection. L'enrichissement de l'air en oxygène a un effet stabilisant sur la flamme, une meilleure efficacité énergétique est remarquée. Le champ magnétique et l'enrichissement en oxygène modifient l'amplitude et la fréquence des instabilités évoquées. Un avantage majeur de ces moyens de contrôle pourrait être une stabilisation de la flamme décrochée a la sortie du brûleur. / Studying and understanding the behavior of diffusion flames becomes of great importance becauseof their presence in different industrial applications. In this study, the laminar diffusion flame isissued from a circular jet of methane and a coaxial jet of air. Two ways are proposed to influencethis flame: the application of a non-homogeneous magnetic field and enrichment of air with oxygen.The effect of these two factors is studied on the flame characteristics (lift-off height and flamelength), its behavior, stability and the instabilities of the upstream flow, the flame base and theflame top (flickering). The effect of the magnetic field depends on the sign of its gradient, and it'sdue to the generation of a magnetic force and the influence on the convection motion. Enrichmentof air with oxygen is having a stabilizing effect on the flame. Magnetic field and oxygen enrichmentcan modify the amplitude and the frequency of different kind of instabilities. The major advantageconsists in the stabilization of the flame on the burner rim.

An experimental study of sooting characteristics of laminar underventillated ethylene non-premixed flames in hot vitiated environments was performed using a modified Wolfhard-Parker co-flowing slot burner. The burner could be operated in "single mode" with a cold air/oxygen mixture as the oxidizer for the non-premixed flame or in varying degrees of "dual mode" where the products of lean premixed hydrogen/air/oxygen flames were used as the oxidizer for the non-premixed flame. Premixed flame stoichiometries of 0.3 and 0.5 were considered for the dual mode cases. Dual mode operation of the burner was intended to simulate the conditions of fuel rich pockets of gas burning in the wake of previously burned fuel/air mixture as typically found in real nonpremixed combustion devices. Dual mode operation introduced competing thermal and chemical effects on soot chemistry. Experimental conditions were chosen to match peak nonpremixed flame temperatures among the cases by varying oxidizer inert (N2) concentration to minimize the dual mode thermal effect. In addition the molecular oxygen (post premixed flame for dual mode cases) and ethylene fuel flow rates were held constant to maintain the same overall equivalence ratio from case to case. Thermocouple thermometry utilizing a rapid insertion technique and radiation corrections yielded the gas temperature field. Soot volume fractions were measured simultaneously with temperature using Thermocouple Particle Densitometry (TPD). Soot volume fraction, particle size and particle number density fields were measured using laser light scattering and extinction. Gas velocities were measured using Particle Imaging Velocimetry (PIV) on the non-premixed flame centerline by seeding the ethylene flow and calculated in the oxidizer flow stream. Porous sinters in the oxidizer slots prevented oxidizer particle seeding required for PIV measurements. In general as the degree of dual mode operation was increased (i.e. increasing stoichiometry of the premixed flames) soot volume fractions decreased, particle sizes increased and soot particle number densities decreased. This trend is suspected to be result of water vapor elevating OH concentrations near the flame front in dual mode operation reducing soot particle nucleation early in the flame by oxidizing soot precursors. The larger particle sizes measured at later stages of dual mode flames are suspected to be the result of lower competition for surface growth species for the lower particle number densities in those flames. Integrated soot volume fraction and particle number fluxes at various heights in the flame decreased with increasing degree of dual mode operation. / Master of Science

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