Soot prediction from combustion systems is still a major challenge in high-fidelity simulations of reactive flows, especially in turbulent conditions. Among the critical aspects, due to its slow characteristic formation times, soot sensitivity to strain rate and turbulence-chemistry interaction models for combustion closure can be found. Starting from the laminar problem, Soot Formation (SF) and Soot Formation Oxidation (SFO) counterflow flames are studied, allowing assessment of the roles of the different underlying phenomena concurring at soot formation with varying strain rates, depending on their relevance in each configuration. Attention is devoted to the inception model, which always regulates the onset of soot formation, and entirely determines the soot sensitivity to strain rate in the SF configuration through nucleation and condensation. Besides, surface growth and oxidation are analyzed in the SFO configuration, where they are predominant. The corresponding models are fine-tuned and generalized, and improved predictions are obtained in both configurations. Afterwards, a 2-points flame-controlling continuation method with soot module inclusion is developed to build a tool capable of flamelets generation inclusive of soot effects on the gas phase. The implementation is first tested discussing general features of the S-curve and verifying the consistency with previous works. The tool is finally used to compute the S-curve of ethylene pressurized sooting flames. The models and tools developed are incorporated into an OpenFOAM-based solver to perform Computational Fluid Dynamic (CFD) simulations of sooting turbulent flames. These are studied in pressurized, highly turbulent environments, to validate the soot model at a fundamental level but with practically relevant operative conditions. The numerical results are found to satisfactorily depict the soot volume fraction (SVF) formation, even though a few quantitative and qualitative discrepancies are discussed. Furthermore, soot intermittency and pressure scaling are analyzed. Finally, an alternative turbulence-chemistry interaction model for combustion closure is explored. A generalized partially-stirred reactor model is developed which accounts for all chemical times in a consistent manner. While the applicability of available models is confined to specific turbulence-chemistry interaction regimes, the incorporation of detailed chemistry description in the proposed approach improves synergistic predictions of all species and makes it suitable for systems with characteristic times very different from each other, such as soot and NOx.

An experimental study was conducted using axisymmetric co-flow laminar diffusion flames of methane-air, methane-oxygen and ethylene-air to examine the effect of pressure on soot formation and the structure of the temperature field. A liquid fuel burner was designed and built to observe the sooting behavior of methanol-air and n-heptane-air laminar diffusion flames at elevated pressures up to 50 atm. A non-intrusive, line-of-sight spectral soot emission (SSE) diagnostic technique was used to determine the temperature and the soot volume fraction of methane-air flames up to 60 atm, methane-oxygen flames up to 90 atm and ethylene-air flames up to 35 atm. The physical flame structure of the methane-air and methane-oxygen diffusion flames were characterized over the pressure range of 10 to 100 atm and up to 35 atm for ethylene-air flames. The flame height, marked by the visible soot radiation emission, remained relatively constant for methane-air and ethylene-air flames over their respected pressure ranges, while the visible flame height for the methane-oxygen flames was reduced by over 50 % between 10 and 100 atm. During methane-air experiments, observations of anomalous occurrence of liquid material formation at 60 atm and above were recorded. The maximum conversion of the carbon in the fuel to soot exhibited a strong power-law dependence on pressure. At pressures 10 to 30 atm, the pressure exponent is approximately 0.73 for methane-air flames. At higher pressures, between 30 and 60 atm, the pressure exponent is approximately 0.33. The maximum fuel carbon conversion to soot is 12.6 % at 60 atm. For methane-oxygen flames, the pressure exponent is approximately 1.2 for pressures between 10 and 40 atm. At pressures between 50 and 70 atm, the pressure exponent is about -3.8 and approximately -12 for 70 to 90 atm. The maximum fuel carbon conversion to soot is 2 % at 40 atm. For ethylene-air flames, the pressure exponent is approximately 1.4 between 10 and 30 atm. The maximum carbon conversion to soot is approximately 6.5 % at 30 atm and remained constant at higher pressures.

This thesis compares ash collected from different boilers cleaned using infrasound cleaning. The samples were evaluated from their physical properties, in an attempt to find connections between the difficulty to remove ash and its physical appearance. To get a deeper understanding of the mechanisms behind adhesion and fouling, and possibly explain results from the study of the ash samples, a literature review was carried out. The ash was also evaluated to see if any connections could be drawn between the physical properties of the ash and its fouling capabilities. A strong connection was found between ash density and its fouling capabilities. It was found that no dry ash with a density higher than 0.4 g/ml were difficult to remove with infrasound cleaning, and no ash with lower density was easy to remove. The ash density was calculated from a measurement of the weight of a certain volume of ash on a scale. Optical microscopy was used to study the ash samples, and gave an estimation of particle size, shape, and porosity. However, no clear connection could be observed with this method between the different samples and which were difficult to remove. The particle size for a few of the samples were also measured by a wet laser sieving method, and while it does give a good picture of particle size, the size was not found to be a useful prediction of the ash fouling behaviour. The exact mechanism giving rise to the density dependence need to be further investigated.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 936-960. / by James D. Bittner. / Sc.D.

Methane-air, ethane-air, and n-heptane-air over-ventilated co-flow laminar diffusion flames were studied up to pressures of 2.03, 1.52, and 0.51 MPa, respectively, to determine the effect of pressure on flame shape, soot concentration, and temperature. A spectral soot emission optical diagnostic method was used to obtain the spatially resolved soot formation and temperature data. In all cases, soot formation was enhanced by pressure, but the pressure sensitivity decreased as pressure was increased. The maximum fuel carbon conversion to soot, ηmax, was approximated by a power law dependence with the pressure exponent of 0.92 between 0.51 and 1.01 MPa, and 0.68 between 1.01 and 2.03 MPa with ηmax=9.5% at 2.03 MPa for methane-air flames. For ethane-air flames, the pressure exponent was 1.57 between 0.20 and 0.51 MPa, 1.08 between 0.51 and 1.01 MPa, and 0.58 between 1.01 and 1.52 MPa where ηmax=23% at 1.52 MPa. For nitrogen-diluted n-heptane-air flames, ηmax=6.5% at 0.51 MPa.

The effects of changing nozzle hole patterns and hole geometry in a direct injection natural gas optically accessible engine was investigated. Six nozzles were studied having a 1 hole, 3 hole, and 9 hole pattern; each having either elliptical or circular hole geometries. Combustion images were taken with a high speed camera and the nozzles were compared on the basis of their ignition delay time, rate of heat release, net heat release, fuel utilization, gross indicated thermal efficiency, and particulate emissions. The best performance in all categories was achieved by the 9 hole nozzles which was largely attributed to better fuel mixing as a result of its hole distribution. The elliptical hole geometry exhibited characteristics of improved mixing mainly through reduced ignition delay time and reduced elemental carbon emissions.

Methane-air, ethane-air, and n-heptane-air over-ventilated co-flow laminar diffusion flames were studied up to pressures of 2.03, 1.52, and 0.51 MPa, respectively, to determine the effect of pressure on flame shape, soot concentration, and temperature. A spectral soot emission optical diagnostic method was used to obtain the spatially resolved soot formation and temperature data. In all cases, soot formation was enhanced by pressure, but the pressure sensitivity decreased as pressure was increased. The maximum fuel carbon conversion to soot, ηmax, was approximated by a power law dependence with the pressure exponent of 0.92 between 0.51 and 1.01 MPa, and 0.68 between 1.01 and 2.03 MPa with ηmax=9.5% at 2.03 MPa for methane-air flames. For ethane-air flames, the pressure exponent was 1.57 between 0.20 and 0.51 MPa, 1.08 between 0.51 and 1.01 MPa, and 0.58 between 1.01 and 1.52 MPa where ηmax=23% at 1.52 MPa. For nitrogen-diluted n-heptane-air flames, ηmax=6.5% at 0.51 MPa.

The effects of changing nozzle hole patterns and hole geometry in a direct injection natural gas optically accessible engine was investigated. Six nozzles were studied having a 1 hole, 3 hole, and 9 hole pattern; each having either elliptical or circular hole geometries. Combustion images were taken with a high speed camera and the nozzles were compared on the basis of their ignition delay time, rate of heat release, net heat release, fuel utilization, gross indicated thermal efficiency, and particulate emissions. The best performance in all categories was achieved by the 9 hole nozzles which was largely attributed to better fuel mixing as a result of its hole distribution. The elliptical hole geometry exhibited characteristics of improved mixing mainly through reduced ignition delay time and reduced elemental carbon emissions.

The European emission standard is an EU directive which describes what emission limits car manufactures are required to meet. In order to meet these requirements car manufacturers use different techniques and components. In a modern diesel automobile a Diesel Particulate Filter (DPF) is used to gather soot from the exhausts. As soot accumulates in the DPF, the back pressure increases and the capability to hold more soot decreases. Therefore the DPF continuously needs to get rid of the stored soot. The soot is removed through a process called regeneration. In order to optimize when to perform regeneration, it is vital to know the amount of soot in the filter. A method for estimating the soot mass in a DPF using a radio frequency-based sensor has been developed. The sensor that has been studied is the Accusolve soot sensor from General Electric. A parameter study has been performed to evaluate the parameters that affects the sensor’s output. Parameters that have been studied include positioning of the sensor, temperature in the DPF, flow rate through the DPF and distribution of soot in the DPF. Different models for estimation of soot mass in the DPF has been developed and analyzed. An uncertainty caused by removing the coaxial cable connectors when weighing the DPF has been identified and methods for minimizing this uncertainty has been presented. Results show that the sensor output is sensitive to temperature, soot distribution and position, and also show some sensitivity to the flow rate. An ARX model, with only one state, is proposed to estimate the soot mass in the DPF, since it gives the best prediction of soot mass and showed good resistance to bias errors and noise in all the input signals.

Extensive research on soot in snow and snow grain size has been carried out in the Polar Regions. However, North American prairie snowpacks lack observations of soot in snow on snow albedo which adds uncertainty to the overall global effect that black carbon on snow has on climate. Measurements in freshly fallen prairie snowpacks in Northwestern Iowa and Central Texas were collected from February 25 to March 3, 2007 and April 6, 2007, respectively. Multi-day monitoring locations and a frozen lake were study sites at which snow samples were collected to measure soot in snow concentrations. Ancillary measurements were collected at a subset of the sample sites that included: temperature, density, depth, and grain size. At some locations snow reflectance and snow radiance was collected with an Analytical Spectral Device visible/near infra-red spectroradiometer (350 ? 1500 nm). Snow impurity, consisting of light-absorbing particulate matter, was measured by filtering meltwater through a nucleopore 0.4 micrometer filter. Filters were examined using a photometer to measure mass impurity concentration. Soot observations indicate prairie snowpack concentrations ranging from 1 ng C gm^-1 to 115 ng C gm^-1 with an average of 34.9 ng C gm^-1. These measurements are within range of previously published values and can lower snow albedo. As expected, spectral albedo was found to decrease with increasing impurities. Additionally, as grain size increased impurity concentration increased. Differences in soot concentration were observed between the two Iowa snowfall events. The Texas event had higher soot concentrations than both Iowa snowfalls. Validation of an ADEOS-II snow product algorithm that compares simulated radiances to measured sensor radiances for retrieval of snow grain size and mass fraction of soot in snow was attempted using satellite images acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS). The algorithm was unable to uniquely identify a particular snow grain size and soot concentration that would lead to a converging radiance solution in the two spectral bands measured and compared by the algorithm. The in situ data at the validation site fell within published ranges for freshly fallen snow for both snow grain size and soot concentration; however; the closest algorithm retrievals were considerably higher than in situ measurements for both grain size and impurity concentrations.