Sensitivity analysis was performed on a soot model using a partially stirred reactor (PaSR) in order to determine the effects of mixing model parameters on soot scalar values. The sensitivities of the mixture fraction zeta and progress variable C to the mixing model constant C_phi were calculated; these values were used to compute the sensitivity of water mass fraction Y_H2O to C_phi and several soot quantities to soot moments. Results were validated by evaluating the mean mixture fraction sensitivity and a long simulation time case. From the baseline case, it was noted that soot moment sensitivities tended to peak on the rich side of the stoichiometric mixture fraction zeta_st. Timestep, number of notional particles, mixing timescale tau_mix, and residence time tau_res were varied independently. Choices for timestep and notional particle count were shown to be sufficient to capture relevant scalar profiles, and did not greatly affect sensitivity calculations. Altering tau_mix or tau_res was shown to affect sensitivity to mixing, and it was concluded that the soot model is more heavily influenced by the chemistry than mixing. / text

The purpose of this research is to develop a dataset for some of the most important fire characteristics, namely CO2 yield, CO yield, HCN yield, soot yield and heat of combustion for probabilistic analysis and modelling. Raw data in time series are required to mechanically reduce experimental data into yields (kg/kg) and effective heats of combustion (MJ/kg), which are expressions for the amount of products generated per unit mass of fuel. Mass loss rate thresholds were applied to all tests to define the beginning and end of tests. These species yields and heat of combustions were then grouped by material compositions and fitted with distribution functions to produce distributions curves. As fire species productions and heat of combustions are dependent on the fire conditions as it develops, different yields are expected at different fire stages. These have been identified as the growth (G), transition (T), and smouldering (S) stages in this research. These values are also compared against, and are generally in agreement with, other research data. Nonetheless, some discrepancies have occurred and require further information to ascertain the material characteristics and combustion conditions. In conclusion, design recommendations for these fire characteristics have been made for several material groupings and verified against other research results. Certain physical and chemical limitations exist for combustions and have not been reflected in the fitted distribution, including stoichiometric yields and unlimited air yields. As such, species yields and heat of combustions beyond these values should not be considered in fire engineering design and analysis. Research results on HCN including all required data parameters for yield conversions were difficult to obtain and require further research efforts. Tube furnace results were initially investigated. Unfortunately, without a continuous mass record, has proved to be challenging in producing reliable mass loss rate profiles for yield conversions. A semi-automated data reduction application UCFIRE was also used. However, certain technical difficulties were encountered and require modifications to broaden its applicability.

This investigation aims to enhance the regeneration performance of a diesel particulate filter. This is achieved by introducing various chemical components to the regeneration process, which are representative of what can be generated ‘on board’ a vehicle using an exhaust gas fuel reformer. By researching the effects of introducing such components using a periodic injection cycle the aim is to reduce the volume of ‘reformates’ required to assist in proficient diesel particulate filter regeneration. As a result, this study also aims to support future work in the development of exhaust gas fuel reformer design for DPF aftertreatment applications. All experiments were performed using a Ford Puma 2.0 litre diesel engine. A test rig was constructed and installed that featured a mini diesel particulate filter housed within a tubular furnace. Exhaust gas could be sampled directly from the exhaust manifold and fed through the DPF. Exhaust gas measurements were taken both pre and post DPF using a FTIR spectrometer. It was shown that the regeneration process could be supported substantially by the introduction of hydrogen. Similar properties were also demonstrated when introducing a hydrogen-carbon monoxide mixture. The introduction of these species allowed for the regeneration process to be implemented at filter temperatures substantially lower than the passive regeneration temperature. Furthermore, by introducing these simulated reformates using a periodic injection strategy, it was evident that similar benefits to the regeneration process could be attained with significantly less volumes of simulated reformates. In an attempt to effectively utilise the carbon monoxide generated during hydrogen production by an exhaust gas fuel reformer, this study defined an optimised hydrogen/carbon monoxide mixture ratio of 60% (v/v) hydrogen balanced with carbon monoxide. At this optimised mixture ratio, the filter demonstrated the highest regeneration efficiency of all ratios tested. Such data could be utilised in future work in the development of fuel reformer design.

The Fire Dynamics Simulator (FDS) code recently developed by the National Institute of Standards and Technology (NIST) is particularly well-suited for use by fire protection engineers for studying fire behavior. It makes use of Large Eddy Simulation (LES) techniques to directly calculate the large-scale fluid motions characteristic of buoyant turbulent diffusion flames. However, the underlying model needs further development and validation against experiment in the areas of soot formation/oxidation and radiation before it can be used to calculate flame heat transfer and predict the burning of solid or liquid fuels. WPI, Factory Mutual Research, and NIST have undertaken a project to make FDS capable of calculating the flame heat transfer taking place in fires of hazardous scale. The temperatures predicted by the FDS code were generally too high on the fuel side and too low on the oxidant side when compared to experimental data from small-scale laminar diffusion flames. For this reason, FDS was reformulated to explicitly solve the conservation of energy equation in terms of total (chemical plus sensible) enthalpy. This allowed a temperature correction to be applied by removing enthalpy from the fuel side and adding it to the oxidant side. This reformulation also has advantages when using probability density function (PDF) techniques in larger turbulent flames because the radiatively-induced nonadiabaticity is tracked locally with each fluid parcel. The divergence of the velocity field, required to obtain the flow-induced perturbation pressure, is calculated from an expression derived from the continuity equation. A new approach to soot modeling in diffusion flames was developed and added to the FDS code. The soot model postulated as part of this work differs from others because it is intended for engineering calculations of soot formation and oxidation in an arbitrary hydrocarbon fuel. Previous models contain several fuel-specific constants that generally can only be determined by calibration experiments in laminar flames. The laminar smoke point height, an empirical measure of a fuel?s sooting propensity, is used in the present model to characterize fuel-specific soot chemistry. Two separate mechanisms of soot growth are considered. The first is attributed to surface growth reactions and is dependent on the available surface area of the soot aerosol. The second is attributed to homogeneous gas-phase reactions and is independent of the available soot surface area. Soot oxidation is treated empirically in a global (fuel-independent) manner. The local soot concentration calculated by the model drives the rate of radiant emission. Calibration against detailed soot volume fraction and temperature profiles in laminar axisymmetric flames was performed. This calibration showed that the general approach postulated here is viable, yet additional work is required to enhance and simplify the model. The essential mathematics for modeling larger turbulent flames have also been developed and incorporated into the FDS code. An assumed-beta PDF is used to approximate the effect of unresolved subgrid-scale fluctuations on the grid-scale soot formation/oxidation rate. The intensity of subgrid-scale fluctuations is quantified using the principle of scale similarity. The modified FDS code was used to calculate the evolution of soot in buoyant turbulent diffusion flames. This exercise indicated that the subgrid-scale fluctuations are quantitatively important in LES of turbulent buoyant diffusion flames, although no comparison of prediction and experiment was performed for the turbulent case.

Measuring the Effects of Mouse Allergen and Black Carbon Exposure on Children Living in New York City with Allergic Diseases Medina Samira Jackson-Browne Background: Exposure to allergens and combustion by-products are risk factors for allergic health outcomes in children. The connection between exposure to allergens and allergic diseases such as asthma, in some children, is through the development of a biological condition known as allergic sensitization. In susceptible children, sensitization may occur when early-life exposure to an allergen causes the production of immunoglobulin E (IgE) antibodies. In asthmatic children, repeated exposures to this allergen may lead to clinical manifestations including airway inflammation, airway mucous production, bronchospasms, and bronchial hyper-responsiveness. Sensitization and repeated exposure to allergens may, therefore, be important risk factors for asthma morbidity in children. Findings from a cross-sectional asthma study of children living in NYC published previously by our group found a positive association between cockroach and dust-mite allergens measured in bed dust and sensitization risk to these allergens consistent with other studies. However, contrary to previously published research, no association was observed between mouse allergen measured in bed dust and mouse sensitization risk in our study. In urban areas such as New York City (NYC), exposure to combustion by-products, including black carbon (BC), has been shown to be associated with both asthma development and asthma morbidity. BC has been proposed to exacerbate asthma symptoms directly through airway irritation or by behaving as an adjuvant, enhancing the production of IgE antibodies following exposure to an allergen in sensitized individuals. Our group previously observed an association between indoor measured BC concentrations and airway inflammation, however no association was found between BC and asthma symptoms for children living in NYC. In the present study, we sought to address some of the limitations of the previous work. These limitations included a singular measurement of mouse allergen exposure, a shorter-term BC exposure measurement, and a cross-sectional study design for asthma symptom risks. My overarching hypothesis for this dissertation is that exposures to mouse allergen and BC are significant risk factors for allergic sensitization and asthma morbidity, respectively, for children living in NYC. I tested these hypotheses in three separate manuscripts by assessing multiple mouse exposure measurements with the risk for mouse sensitization (Chapter 2), testing the correlation between 7-day measured indoor BC and particulate matter smaller than 2.5 microns (PM2.5) concentrations with annual modeled outdoor BC and PM2.5 concentrations (Chapter 3), and determining whether annual modeled outdoor BC concentration is associated with persistent asthma symptoms, over a three-year period, for asthmatic children in NYC (Chapter 4). Methods: For all manuscripts, data from an asthma case-control cohort of children (age 7-8 years) previously established by our group, the NYC Neighborhood Asthma and Allergy Study (NAAS), was utilized for analysis (n=350). Kitchen floor and bed settled dust samples were collected from the children’s home during the initial home visit. Mouse allergen concentrations were quantified from both kitchen floor and bed dust samples using an enzyme-linked immunosorbent assay (ELISA). Blood samples were also collected during this visit. IgE antibodies to mouse allergens were measured by ImmunoCAP (Phadia, Uppsala, Sweden) from these blood samples. Information on the frequency of mouse sightings in the previous 12 months was extracted from a questionnaire administered to parents of NAAS children. Neighborhood and school mouse sightings were collected from reports from the NYC Department of Health and Mental Hygiene (DOHMH). Indoor PM2.5 and BC samples were collected from air samplers placed in NAAS children’s home for an average of 7 days. In collaboration with the NYC DOHMH, we were given access to 2-year averaged modeled outdoor PM2.5 and BC concentrations collected from air monitors at 124 street-level locations throughout NYC from 2008-2010. After the initial home visit, asthmatic NAAS children were followed-up annually for asthma symptoms. The questionnaire data collected from the asthmatics followed were used to evaluate the persistence or remittance of asthma symptoms over the 3-years following the initial home visit. Results: In our mouse study we found that increasing mouse allergen measured from kitchen floor dust and children whose parents reported greater than weekly mouse sightings in the previous 12 months has an increased risk of mouse sensitization (prevalence risk (PR) = 1.09 [1.02-1.17], p=0.04 and PR= 3.84 [1.95-6.97], p=0.001 respectively). Neither mouse allergen measured from settled bed dust (PR = 1.06 [0.95-1.19], p=0.46) nor neighborhood rodent reports (PR = 1.25 [0.94-1.68], p=0.16) were significantly associated with an increased risk of sensitization to mouse. Exposure to mouse at school was also not associated with an increased risk of mouse sensitization (PR=0.66 [0.35-1.26], p=0.30). Results from the correlation study indicated both annual modeled outdoor PM2.5 and BC concentrations were weakly correlated with 7-day measured indoor PM2.5 and BC concentrations (r = 0.21 and 0.39, respectively, p < 0.01). However, annual modeled outdoor BC concentrations predicted almost 20% of the variability of 7-day measured indoor BC (R2=0.19, p<0.001) compared to only 4% of the variability of 7-day indoor PM2.5 explained by annual modeled outdoor PM2.5, which predicted measured indoor PM2.5 (R2 = 0.04, p < 0.001). Our regression analysis of the asthma morbidity study found no significant association between longer-term neighborhood modeled BC concentrations at study participant’s home (PR = 0.87 [0.58-1.29, p=0.49] and school addresses (PR =1.09 [0.77-1.56], p=0.60) and persistent asthma symptoms. Conclusions: My findings suggest that mouse allergen measured from kitchen floor dust and parent reported mouse sightings are important risk factors of mouse sensitization for children living in urban areas such as NYC. The results of the BC analysis indicate a moderate correlation between annual modeled outdoor BC concentrations and 7-day measured indoor BC concentrations. The annual modeled outdoor BC also predicted 20% of the variability in 7-day measured indoor BC. Conversely, PM2.5 analysis indicate that annual modeled outdoor PM2.5 is not correlated with 7-day measured indoor PM2.5 concentrations. Finally, regression analysis of BC exposure and asthma morbidity indicate that annual modeled outdoor BC is not predictive of persistent asthma symptoms in our cohort.

Factors that may govern diesel particulate matter (DPM) oxidation at low temperatures (~200°C) were studied using reactivity and TP-ToFSIMS analysis. Best-case scenarios that give maximum gasification rates were determined for DPM impregnated with KOH and non-catalyzed DPM using temperature programmed oxidation and isothermal experiments. Conditions of intimate catalyst-carbon contact (K/C molar ratio=1/50) and high NO2 concentrations (1%) to improve the reactivity of the carbon reactive sites were unable to meet the steady state gasification rate needed for particulate filter regeneration for a modern diesel engine at 200°C. Oxygen-free thermal annealing (>500°C) caused reactivity losses of a maximum of 40% that correspond to changes to surface morphology and/or concentration of oxygen-containing functional groups. TP-ToFSIMS identified surface functional group changes with temperature on non-dosed and NOX pre-dosed (1.5%NO, 1%NO2, 4.5%O2, balance helium) diesel soot and sucrose char. Detailed analysis of the NOX dosed sucrose char spectra using both inspection and principal component analysis techniques revealed that the 1200 ion fragments created could be reduced to five sets of ions that are chemically and kinetically distinct. These sets presumably represent surface functional groups on the carbon. For example, Set IV may represent carboxylic acid, lactone, or carboxylic anhydride functional groups. Based on these results a mechanism for the surface reaction of NO2 with carbon under vacuum conditions was postulated. At temperatures less than 200°C the ion fragments contain primarily carbon-NO2 type ions. As temperature increases between 200 and 400°C the ion fragments are primarily carbon-NO and carbon-N type fragments. At higher temperatures (>500°C) the surface is enriched with nitrogen containing functional groups. A surface reaction mechanism is proposed where NO2 is bonded to an armchair site and with increasing temperatures and molecular rearrangements the N is incorporated into the carbon ring. The initial surface composition of NOx containing functional groups changes within the area of relevance of low temperature soot regeneration (i.e. between 25° and 200°C). Further studies are needed to understand the effect of N-incorporation on carbon reactivity. No rate processes either in reactor studies or based on surface functional groups met the rate criteria for low temperature DPM oxidation.

Factors that may govern diesel particulate matter (DPM) oxidation at low temperatures (~200°C) were studied using reactivity and TP-ToFSIMS analysis. Best-case scenarios that give maximum gasification rates were determined for DPM impregnated with KOH and non-catalyzed DPM using temperature programmed oxidation and isothermal experiments. Conditions of intimate catalyst-carbon contact (K/C molar ratio=1/50) and high NO2 concentrations (1%) to improve the reactivity of the carbon reactive sites were unable to meet the steady state gasification rate needed for particulate filter regeneration for a modern diesel engine at 200°C. Oxygen-free thermal annealing (>500°C) caused reactivity losses of a maximum of 40% that correspond to changes to surface morphology and/or concentration of oxygen-containing functional groups. TP-ToFSIMS identified surface functional group changes with temperature on non-dosed and NOX pre-dosed (1.5%NO, 1%NO2, 4.5%O2, balance helium) diesel soot and sucrose char. Detailed analysis of the NOX dosed sucrose char spectra using both inspection and principal component analysis techniques revealed that the 1200 ion fragments created could be reduced to five sets of ions that are chemically and kinetically distinct. These sets presumably represent surface functional groups on the carbon. For example, Set IV may represent carboxylic acid, lactone, or carboxylic anhydride functional groups. Based on these results a mechanism for the surface reaction of NO2 with carbon under vacuum conditions was postulated. At temperatures less than 200°C the ion fragments contain primarily carbon-NO2 type ions. As temperature increases between 200 and 400°C the ion fragments are primarily carbon-NO and carbon-N type fragments. At higher temperatures (>500°C) the surface is enriched with nitrogen containing functional groups. A surface reaction mechanism is proposed where NO2 is bonded to an armchair site and with increasing temperatures and molecular rearrangements the N is incorporated into the carbon ring. The initial surface composition of NOx containing functional groups changes within the area of relevance of low temperature soot regeneration (i.e. between 25° and 200°C). Further studies are needed to understand the effect of N-incorporation on carbon reactivity. No rate processes either in reactor studies or based on surface functional groups met the rate criteria for low temperature DPM oxidation.

Heterogeneous freezing processes in which atmospheric aerosols act as ice nuclei (IN) cause nucleation of ice crystals in the atmosphere. Heterogeneous nucleation can occur through several freezing mechanisms, including contact and immersion freezing. The mechanism by which this freezing occurs depends on the ambient conditions and composition of the IN. Aerosol properties change through chemical aging and reactions with atmospheric oxidants such as ozone. We have conducted a series of laboratory experiments using an optical microscope apparatus equipped with a cooling stage to determine how chemical oxidation changes the ability of atmospheric aerosols to act as IN. Freezing temperatures are reported for aerosols composed of fresh and oxidized soot and polyaromatic hydrocarbons (PAHs) including anthracene, phenanthrene, and pyrene. Our results show that oxidized soot particles initiate ice freezing events at significantly warmer temperatures than fresh soot, 3 °C on average. All oxidized PAHs studied had significantly warmer freezing temperatures than fresh samples. The chemical changes presumably causing the improved ice nucleation efficiency were observed using Fourier Transform Infrared Spectroscopy with Horizontal Attenuated Total Reflectance (FTIR-HATR). The addition of C=O bonds at the surface of the soot and PAHs led to changes in freezing temperatures. Finally, we have used classical nucleation theory to derive heterogeneous nucleation rates for the IN compositions in this research. The overall efficiency of the IN can be compared in order of least efficient to most efficient: fresh phenanthrene, fresh anthracene, fresh soot, oxidized phenanthrene, fresh pyrene, oxidized anthracene, oxidized soot, and oxidized pyrene. Overall oxidation of aerosols increases their ability to act as IN. Our results suggest that oxidation processes facilitate freezing at warmer temperatures at a broader range of conditions on the atmosphere.

No description available.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 160 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 120-122).