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Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The black carbon particulate matter (soot) emissions from internal combustion engines have negative health and climate impacts. PM emissions are typically characterized with modest temporal resolutions; however, in-cylinder investigations have demonstrated significant variability and the importance of individual cycles. Detecting such variations in the exhaust requires measurements close to the exhaust valve, which are not possible with the current sensors. Here, a methodology for characterizing the cycle-specific PM concentration at the exhaust-port of a single-cylinder research engine is developed using a light-scattering sensor, the Fast Exhaust Nephelometer (FEN).The FEN light scattering is converted to soot mass concentration (Cₘ) and mass-mean mobility diameter (dm,g) using an inversion algorithm based on the Rayleigh-Debye-Gans model for fractal aggregates (RDGFA). The model incorporates the external mixing hypothesis (EMH) to correlate the diameter of primary particles with the aggregates. The inversion parameters are obtained from Transmission Electron Microscopy (TEM) and literature, resulting in Cₘ and dm,g that are within ±10% of the reference methods. The results could vary by ±40% due to uncertainties in the RDGFA parameters; however, by incorporating the EMH morphology model, the variations are reduced to within ~ ±25% of the reference measurements.The response time of the FEN, determined from a “skip-fired” scheme by disabling the fuel injection, is on average 55 ms. This is well below the engine cycle period (~100 ms) for the considered engine speeds. A cycle-specific PM mass averaging method was developed based on the characteristics of the exhaust-port signals. Using this cycle-resolved method, it is shown that the cycle-to-cycle coefficient of variation of Cₘ is 40%, while the in-cylinder gross indicated mean effective pressure (GIMEP) varies by 2%. Despite their different ranges of variation, the cycle-specific Cₘ and GIMEP are negatively correlated with R² ~ 0.2-0.7, where cycles with low GIMEP emit more soot. The physical causes of this association deserve further investigation, but are expected to be caused by local fuel-air mixing effects. The methods and findings of this work can further our understanding of the engine variability under transient conditions, and assist the interpretation of the in-cylinder variations observed in optical engine experiments.
Membrane-based energy recovery ventilators (ERVs) improve building energy efficiency by transporting heat and moisture between incoming and outgoing air streams. Although long-term studies are not available due to the recent implementation of this technology, there are preliminary indications that moisture transport might degrade with the extended operation, possibly as the result of exposure to air pollution or other environmental stresses. The scope of this dissertation is to quantify the influence of environmental factors on the permeation properties of current-generation composite membranes and the overall performance of ERV exchanger cores.First, the impact of particulate fouling was investigated via accelerated membrane- and core-level fouling experiments. The core-level experiments showed minimal impact on the effectiveness of ERV cores from coarse dust loadings. However, membrane-level examination with aerosol nanoparticles indicated that moisture transport through membranes was especially impaired when particles were hygroscopic or contained liquids. These results suggest that the optimal protection by filters and the orientation of the membrane would depend on the nature of the indoor and outdoor aerosols.Second, the effects of relative humidity and temperature on the transport of water vapor and CO₂ (as a surrogate for indoor air pollutants) was evaluated through a systematic study of some standard polymers suitable for ERV use. It was shown that the permeability and selectivity of membranes could vary up to an order of magnitude depending on the membrane material, the temperature and relative humidity on both feed and permeate sides of the membrane, as well as orientation in asymmetric composite membranes. A theoretical model for predicting permeability of composite membranes, based on a limited number of kinetic water vapor sorption tests of the selective coating polymer, was successfully developed and validated for a commercial membrane. This model was then coupled with a heat and mass transfer model of cross-flow ERV exchanger cores to interpret the membrane-level variations regarding ERV exchanger core performance. A study of the effects of outdoor air parameters showed that the effectiveness of ERV exchangers could increase or decrease significantly with outdoor air relative humidity, while outdoor air temperature had only a minimal influence on effectiveness parameters.
Accurate measurement of the properties, emission rates, and environmental impacts (i.e. climate forcing) of aggregated aerosols depend on precise measurement of their morphology (i.e. primary particle diameter, dp, and its polydispersity).For decades soot has been modeled as fractal-like aggregates of nearly equiaxed spherules. However, examination of the soot particles collected from different combustion environments shows that the larger aggregates contain larger primary particles and the variation in dp is much smaller within individual aggregates than between aggregates.In addition to this size dependency, measurements of optical properties of mass-classified soot particles revealed that the mass-specific absorption cross section of soot also depends on particle mass. This along with the correlations observed between dp and aggregate size, suggest that these aggregates are formed in relatively homogeneous microscopic regions; after which particles with different formation, growth, and oxidation histories are mixed. This suggests that there is a need for accurate estimation of primary particle size distribution and refinement of assumptions commonly used in the conventional simulations and interpretation of the measurements.Morphology characterization of the agglomerates is commonly performed by labor-intensive manual analysis of the images produced by transmission electron microscopy. A new method has been developed for automatic determination of dp based on the variation of the 2-D pair correlation function. Results obtained from this method approximately deviate ~4% from the manual method. Application of this method is not limited to the soot particles and it can be applied to any type of the agglomerates. As an alternative approach, indirect in situ mass-mobility method proposed for the estimation of dp in zirconia particles has been tested and calibrated for soot particles. It was found that with some calibration, this method can provide results with useful accuracy.Polydispersity of the primary particles has also been neglected in the previous investigations of the hydrodynamic properties of clusters. It was shown that the mobility-equivalent diameter and the overall size of the agglomerates not only depend on dp but also increase substantially with its polydispersity. New correlations were developed for the free-molecular and continuum mobility diameters using stochastic projection and Stokesian Dynamics methods, respectively.
Internal combustion engines produce emissions of NOx and particulate matter (PM). Westport Innovations Inc. has developed the pilot-ignited high-pressure direct-injection (HPDI) natural gas (NG) engine system. To ignite the natural gas, HPDI uses a small diesel pilot injection (~5% of total fuel energy), which is normally injected before the NG. Although HPDI engines produce less PM than diesel engines, further reductions of engine-out PM emissions are desired in order to meet future regulations. The goal of this project is to reduce PM from HPDI engines and study the drawbacks of the injection strategies in terms of engine performance or other emissions. This thesis proposes mechanisms for two injection strategies useful in PM reduction: Late Post Injection (LPI) and Slightly Premixed Combustion (SPC). Tests on LPI and SPC were performed in the UBC Single Cylinder Research Engine (SCRE). In LPI, a second natural gas injection (10-25% of total fuel mass) is injected into the cylinder later in the cycle. In SPC, more premixing of NG is achieved by injecting NG before the diesel injection and engine operating parameters are adjusted to minimize the effect on other emissions. Both of the injection strategies show significant PM reduction (over 75% on the SCRE) with small effects on other emissions and engine performance. Westport’s computational fluid dynamics package, “GOLD”, was used to help to understand the mechanisms of the new injection strategies. The PM reductions from LPI and SPC were captured by GOLD.A phenomenological model (Transient Slice Model, TSM) has been developed in this study to provide better insight into the PM reduction process, using the Hiroyasu model with a transport equation for soot. TSM results show good agreement in the prediction of pressure trace and heat release rates in most cases. Engine-out PM trends with changing engine parameters are well-captured in the TSM for exhaust gas recirculation (EGR), equivalence ratio (EQR), load and natural gas (NG) flow. TSM cannot predict the effect of NG injection pressure. For the new injection strategies, TSM can predict the PM trends for LPI, relative gas-diesel timing and the SPC injection strategy.
Air filtration is used to reduce particle concentrations in the indoor environment to provide improved occupant health due to reduced exposure. Increased focus on occupant health in emerging design standards is leading to the installation of higher efficiency filtration systems. These systems generally have higher resistance to flow and therefore impose a greater energy penalty. Previous air filter models have used simplified assumptions with regards to the dynamics of filter operation, which have limited the potential to determine energy efficiency or optimization approaches to system design and operation. This dissertation focuses on developing an improved air filter model to investigate the potential for system modifications to reduce energy consumption and improve indoor air quality (IAQ) within commercial buildings.A new air filter performance model was developed using generalizable results from ASHRAE Standard 52.2-2012 and validated against laboratory and real-world experiments. The results showed better agreement with laboratory tests than with real operation. The filter model was combined with existing indoor particle dynamics and epidemiological models to determine the impacts of changes to system operation through monetization of operation costs and health benefits. Laboratory experiments were performed to evaluate the role that particle properties and relative humidity play in determining the filter performance changes with the aim of better understanding the reasons for discrepancies in operation between laboratory and field filter tests.Operation can now be optimized by accounting for dynamic characteristics of filter performance. Benefits of improved filtration efficiency were found to outweigh added costs. Adopting specific indoor particle concentration limits is recommended to replace existing specifications relying on filter efficiency. System designs can then be optimized to account for local particle concentration and energy costs. A number of system design changes have been highlighted that allow for simultaneous reduction in operation cost and indoor particle concentrations. Relative humidity has been identified as a critical parameter in filter performance and standardized tests should be modified to account for variability in relative humidity and particle characteristics typical of real operation to allow for improvements to future model predictions. Supplementary materials: http://hdl.handle.net/2429/54056
Concerns about the environment, energy costs, and airborne infection risk have revived interest in ventilation systems for health care facilities. Low energy ventilation systems (e.g. stratified air ventilation) have received attention as a means of providing a better air quality at a lower energy cost. The sensitivity of such ventilation systems to boundary conditions in removing airborne contaminants produced by expiratory injections is of concern and studied experimentally and numerically in this work. A three step methodology is adopted. First, an air-assist internally mixing atomizer is developed to generate a poly-disperse distribution of droplets for ventilation testing. A series of near-field experiments reveal droplet size, velocity, and diffusivity in radial and axial directions for steady and transient atomization. Second, the atomizer is used to inject droplets into a mock-up of a patient recovery room with an underfloor air distribution ventilation system. A series of far-field size-resolved concentration measurements are conducted at locations representative of an occupant (receptor). Third, Computational Fluid Dynamics (CFD) simulations are used to predict airborne droplet exposure among various cases in the far-field experiments. Both tracer gas and discrete phase approaches are implemented. Based on the findings we recommend guidelines for ventilation design and room usage in real single patient hospital recovery rooms with stratified ventilation systems. It is desired to have expiratory injections at low momentum, preferably directed towards the walls or upwards. It is also advisable that occupant suspects spend most of their time away from the injection source, possibly at the corner of the room or behind the source. The variations in occupant thermal plume is not likely to affect exposure to airborne droplets in statistically significant ways. It is advisable to used air change rates greater than four since expiratory injections are likely to break down the vertical contaminant stratification. It is likely that dispersion rates be higher for sub micrometer droplets but lower for larger droplets. This has implications for ventilation design strategy as a function of pathogen or pathogen carrying droplet size.
Soot particles are often internally mixed with non-absorbing organic which enhances light scattering and absorption, but the magnitude of this enhancement is highly uncertain. A better characterization of optical properties of coated soot is critical for interpreting optical soot measurements. Simulations using numerically generated aggregates were performed to assess the impact of coatings on the optical properties. A cluster-cluster aggregation algorithm was used to produce aggregates (Df = 1.78 and 2.1) containing 15–600 primary particles with dp = 30 nm. The optical properties were calculated using the discrete-dipole approximation (DDA). For uncoated aggregates, their optical properties were compared with the Rayleigh-Debye-Gans. It was found that the aggregates with similar fractal dimension and prefactor produced by the two methods showed small variations on the optical cross sections. Two coating models were considered: concentric coating and droplet sphere. For the first model, DDA predicted larger absorption than the volume-equivalent core-shell Mie. The coating also caused increase in the discrepancy between the scattering predicted by DDA and the core-shell Mie. For the second model, the aggregates exhibited less absorption and more scattering compared to the concentrically coated aggregates with similar coating fraction, highlighting the importance of coating configurations on the optical properties of coated soot.Laboratory experiments on particles coated with transparent organic were conducted to investigate the changes in the aggregate structure and scattering. Palas particles (dmobility ≈ 118 nm) were employed as proxy for soot and oleyl alcohol was used as the coating. The results of the experiments confirmed that the aggregate-like particles underwent collapsing as the coating was added. The aggregate was fully collapsed (dmobility ≈ 78 nm) when coating mass ratios ≈ 1.75. The coating also enhanced the scattering of coated Palas by a factor of around 2 – 15 depending on the coating amount. The comparative study between the nephelometer scattering from the experiments and the corresponding volume-equivalent Mie were done. The scattering of the uncoated and coated aggregate when aggregate restructuring still occurred were significantly lower compared to the Mie estimations. As the particles fully collapsed, however, their scattering could be accurately predicted from the Mie theory.
Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
The world is in critical need of technologies that will make a significant andimmediate impact in our fight against climate change. As global temperaturesrise, building cooling demands could rise by 72% by the year 2100,meaning that the development of energy efficient space cooling technologiesis becoming increasingly important. Radiant cooling panels have shown a lotof potential as an energy efficient method of supplying space cooling. However,they need to operate alongside dehumidification in many environmentsso that air moisture does not condense on their chilled surfaces.This thesis focuses on the development of the membrane assisted radiantcooling panel, a technology used to provide energy-efficient space cooling inhot and humid climates without the need for mechanical dehumidification.A heat balance model is developed that estimates the operational membranetemperature and cooling capacity of a membrane assisted panel. The modelis then calibrated using data collected from a field experiment in Singapore.Additionally, a framework is developed that allows the heat transfer modelto operate within a TRNSYS environment. This allows for the energy simulationof buildings that utilize membrane assisted panels for sensible spacecooling. The framework is then used to predict the potential energy savingsthat could be obtained by implementing this technology in both Singapore and Vancouver.The membrane temperatures predicted by the calibrated heat transfermodel differ from those observed through experimentation by 0.21°C. Themodel is sufficiently accurate for condensation mitigation, however, concernsregarding the coefficients used to model natural convection, along with thedata used for calibration, need to be addressed before the model can beapplied to different panel geometries. While some aspects of the TRNSYSframework need to be further developed, it was found through simulationthat membrane assisted radiant cooling can provide significant energy savingsin both tropical and temperate climates.The framework developed in this study will bring membrane assistedradiant cooling closer to widespread implementation, as modelers will beable to optimize the design of a radiant system before its construction in abuilding.
Soot is an important contributor to climate change and has negative effects on human health. These impacts depend on the morphological properties which influence the optical properties, mobility and surface area available to adsorb other contaminants. Different combustion sources may produce soot with different morphologies and thus, different environmental and health impacts. Three soot sources were studied: a dual-fuel natural gas marine engine and two laboratory gas flares. The ship studied operated on its normal route during the measurement campaign and was run both in dual-fuel mode, and diesel-only mode to serve as a comparison. Dual-fuel mode produced substantially less soot, ~96% less, than diesel-only mode at all loads except idle. Soot morphology appeared to be independent of operating load but did vary slightly based on fuelling mode. Dual-fuel mode produced on average smaller aggregates than diesel-only mode however, the small dual-fuel mode aggregates tended to have slightly larger primary particles when compared to diesel-only generated aggregates. Overall the differences in morphology are small compared to the reduction in the amount of soot produced. Gas flaring is used in the oil and gas industry to dispose of gas. The laboratory flares studied were designed to simulate conditions which would be found in the upstream oil and gas industry. Raman spectroscopy showed that the heavier fuels had more graphitic nanostructures and transmission electron microscopy (TEM) and mobility size distributions showed that the aggregates tended to be larger. The relationship between the primary particle size and the aggregate size, did not depend on the fuel. During hydraulic fracturing operations, it is likely that the flowback fluids become entrained in the flare fuels resulting in liquids with inorganic salts becoming part of the combustion process. The morphology of the soot did not change due to the salt however, most of the soot particles became internally mixed with the salt. Unlike soot, salt tends to be an effective cloud condensation nucleus (CCN) and the large number of salt particles will likely influence local cloud formation. Furthermore, the salt particles which attach to the soot may turn the soot itself into an effective CCN.
The suitability of Sound Decay per Doubling of Distance (??₂), as a universal room acoustics rating parameter was investigated.??₂ was combined with the Speech Transmission Index (???) to rate acoustical room quality. This follows the methodology of ISO 3382-3, allowing evaluation of room quality using speech intelligibility as a foundation quantity.To prescribe rating criteria, all rooms where unamplified speech is present were postulated to be categorizable into one of three room types: Case 1 (intelligibility) rooms where intelligibility is required at all distances, Case 2 (distraction) rooms where distraction is permissible until a defined distance, or Case 3 (privacy) rooms where privacy is expected beyond a defined distance. For rating metrics, Case 1 used listening effort, Case 2 used loss of productivity, and Case 3 used percentage of speech intelligible.An idealized initial tool was developed which calculates ??? at all points along a ??₂ curve. The tool calculated ??? based only on reverberant speech and was therefore applicable only to rooms where direct speech is impeded by obstacles.Assumptions used in the initial tool were checked using experimental data collected in 62 rooms of varying case classifications from 22 buildings. The data were used to evaluate the accuracy of regressions using sound pressure level measurements over a limited range of 1 – 16 m (??2,?,?,1−16?,), the octave band variation in ??2, and the sound pressure level at 1 m from a sound source. The maximum regression error for ??2,?,?,1−16?, was 5.6 dB, and 2.5 dB on average.DL2 trends observed in the experimental data were then implemented in the DL2 tool and the STI calculation model was updated to include direct speech contributions.The updated tool was used to evaluate theoretical rooms for each case using the developed rating schemes. Room reverberation time (RT, ?) and background noise levels (BNL, ??) were modeled using values recommended in standards.Due to the variability of RT and BNL within rooms of similar types, standardized rating schemes based on ??₂ were deemed unfeasible. However, ??₂ and the tool developed provide valuable insight on how to optimize rooms acoustically. Supplementary materials available at: http://hdl.handle.net/2429/73596.
Soot is one of the important contributors to climate change and has adverse effects on humans’ health and the environment. Some of these impacts can be modeled based on the soot morphological and material properties that influence the optical properties of the soot. Uncertainties around the optical properties can lead to unreliable climate prediction models; therefore, accurate modeling and calculation of soot optical properties can mitigate this issue. A new model is implemented using existing equations to describe the relationship between aggregate size and their primaries: the external mixing hypothesis (EMH). The EMH model is based on the recent studies for non-premixed flames, which quantifies the relationship between primary particle diameter and aggregate mobility diameter based on the mass-mobility exponent and the effective density. Compare to the constant primary particle size assumption and using the Rayleigh-Debye-Gans theory for fractal-like aggregates (RDG-FA) as the optical model, EMH demonstrates an increase in size-dependent and the total mass-specific scattering cross-section (MSC), which is an essential factor in climate modeling. RDG-FA neglects spherule-to-spherule interactions, which reduce its accuracy. In the next step, the multiple-sphere T-matrix method (MSTM) is used as the optical model. A previously published database of MSTM is coupled with the EMH. EMH-MSTM is able to model the variation of mass-specific absorption cross-section (MAC) for different aggregate sizes, which is not resolved by RDG-FA. The MSTM results show that size-dependent and total MAC and MSC levels are increased relative to the RDG-FA predictions, as expected, due to sphere-sphere interactions. Next, an experiment at the University of Alberta used a laboratory buoyant turbulent diffusion flame to produce soot for the model’s validation. Based on the model results, the best agreement can be expected to be for Dm ≈ 2.6, ρ(eff,100) ≈ 600 kg/m^3 and σp|dm ≈ 1.5 for the model and experiment datasets. The uncertainty around the refractive index and other variables such as mass-mobility exponent and the effective density may have caused this inconsistency between model and experiment MSC results. Providing more accurate input information to the model can increase its ability to estimate the optical footprint of the soot aggregates.
The combustion of natural gas is an interesting alternative to liquid fossil fuels due to its competitive price and lower CO₂ emissions. One technique to burn natural gas inside direct-injection engines is the hot-surface ignition-assist method. The natural gas jet impinges on the hot surface, which acts as an ignition source. As a constant high temperature is required in the hot surface to have quick and consistent ignition events, a numerical prediction of the temperature of an application of the hot surface technique was done, and a method to study the temperature of the hot surface was developed. One proposed application of the hot-surface method consists in a fuel injector equipped with a heater ring. The high temperature of the heater could produce an excessive temperature in the injector, affecting its functioning or the fuel. To study this, heat transfer simulations were performed. A sensitivity analysis revealed a large effect of the coolant temperature in the temperature of the injector, and a large effect of the input power and surface emissivity on the temperature of the heater. With an input power of 100 W, the injector temperature is expected to remain within 200 °C, while the heater reaches a temperature beyond 1300 °C. During the injection of the fuel, the hot surface experiences a rapid cooling event. This can affect the ignition delay, hampering the combustion efficiency. To study this, a pyrometer method with high spatial and temporal resolution was developed. A hot surface was subject to a series of cooling jets. The pyrometer method revealed that the jets with a direct orientation produced a larger temperature drop compared to jets with a side orientation, regardless of their pressure or duration. The thermometer method developed has the potential to be used in different applications where rapid changes in temperature are expected, allowing to calculate the temperature of a surface in transient-state using a digital camera and the radiation intensity at a single wavelength.
Modeling sound transmission is a challenging task. An existing beam-tracing model for empty, parallelepiped rooms with specularly-reflecting surfaces is extended to predict room-to-room sound transmission between a source and receiver rooms separated by a common wall. This wall is modeled as one locally-reacting homogenous partition with frequency-independent transmission loss. Besides, sound transmission is modeled in Ray-Tracing (CATT-TM) and FEM (COMSOL). A reference configuration consists of two identical reverberation rooms is chosen following the recommendations of the literature and most of the prescriptions of the reverberation room standard, ASTM 3423. The capability of various room-to-room predictions models, in particular, the phase and energy-based beam tracing models (PBTM, EBTM) in reproducing the results of the diffuse-field theory is investigated. Both EBTM and CATT-TM are found to be reasonably accurate in reproducing the diffuse sound field for a reverberation room (i.e. for diffuse sound fields). However, the predicted levels deviate considerably from the diffuse-field theory with changes in the acoustical characteristics of the room (room aspect ratio, the magnitude of the surface absorption and surface absorption distribution (i.e. for non-diffuse sound fields). EBTM has been validated in both source and receiver rooms through existing results from ODEON in the literature and by comparing the prediction results with the new CATT-TM for the reference configuration. PBTM has been compared with finite element method (COMSOL) results in the low-frequency region. Both phase-based models match well in source room with a reasonable discrepancy. However, the PBTM has not reproduced the sound field predicted by COMSOL in the receiver room. Moreover, Waterhouse effect is studied by both PBTM and EBTM model in the reverberation rooms which is ignored in the classical diffuse-field concept. However, its significant effect is exhibited near the reflecting boundaries inside the reverberation room only in the PBTM predictions. Hence, based on recommendations of the ASTM standards during measuring sound transmission between rooms, sources and receivers should be placed sufficiently far away from the reflecting surfaces, edges and corners of the rooms to avoid the errors due to the Waterhouse effect.
Energy Recovery Ventilators (ERVs) save energy by recovering sensible and latent heat from exhaust ventilation streams. They consist of compact channels in a cross- or counter-flow arrangement separated by moisture-permeable membranes. This work employs computational fluid dynamics with experimental validation to study angled rib mixing features to enhance heat and mass transport in membrane-based ERVs. The model simulates air-to-air heat and mass exchange between two rectangular ducts in a counter-flow arrangement. Local results from these simulations are used in a mathematical model to predict the effectiveness of a cross-flow ERV. The flow is steady and laminar. The channels are modeled with and without ribs for various channel aspect ratios and flow rates. Periodic inlet/outlet conditions are assumed for all cases to highlight the effect of the ribs. Ribs are either on the membrane surface or the opposite wall, however ribs on the membrane surface are the focus of this work due to their superior performance. Results show that the ribs increase the channel Sherwood and Nusselt numbers by a larger fraction than the corresponding increase in friction factor. The improvement is larger for sensible recovery than latent recovery because the membrane’s mass-transfer resistance is higher than its thermal resistance. For a typical commercial grade, counter-flow ERV, total effectiveness can be improved by over 10% for an equal pressure drop by adding ribs and slightly increasing the channel height. Mass-transfer and pressure drop results from the simulations were validated experimentally for channels with and without ribs using a commercially available membrane (dPoint Technologies). Ribs were either formed into the membrane surface or made as extensions of the channel wall. The experimental and simulation results agree with one another within the experimental uncertainty of the test apparatus and variability of the membrane permeability.Typically, ERV performance targets (recovery effectiveness, pressure drop) are met by varying the channel dimensions or number of channels. The work presented here indicates that angled ribs could be used instead, which would not require altering the ERV footprint or using extra materials.
Direct injection of natural gas in compression-ignition engines offers benefits such as emissions reduction, fuel diversity, and energy security. However, in order to meet the upcoming stringent emissions regulations, further improvements in the performance of the High-Pressure Direct-Injection of Natural Gas (HPDI-NG) is needed. For this reason, different natural gas injection strategies and nozzle designs are numerically studied.The in-cylinder phenomena during the closed portion of the cycle is simulated using a Large-Eddy Simulation (LES) turbulence model and the Trajectory-Generated Low Dimensional Manifold (TGLDM) for chemistry coupling. Soot is modeled with a two-equation Hiroyasu model. To partially investigate the effect of LES variability, simulations with successive mesh refinements and infinitesimally varied inputs are carried out. Anticipated emission trends were observed for parametric sweeps with substantial variation of soot about the trend-line. This motivated the analysis of in-cylinder mixture, jet penetration and other more robust metrics.A novel paired-nozzle geometry was designed to increase the fuel-air mixing at the base of the jet, thus reducing soot. In reality, the paired jets increased exhaust PM. The CFD analysis revealed that the gas jet penetration was reduced compared to the baseline single-hole jet, while more air was entrained into the core of the jet. However, the effect of mixing due to impaired penetration dominates and results in more rich mixture and therefore more soot.CFD predicted the PM reduction benefits of “Late Post-Injection” (LPI) due to two major reasons: 1- the reduction in formed PM from the 1st pulse due to shortened pulse width, 2- negligible PM formation from the 2nd pulse for enough pulse separation. A second injection strategy, “Slightly Premixed Combustion” (SPC) also reduced PM in experiments. The CFD package had not been developed for such combustion regime, wherein the diesel-gas kinetic interactions should be resolved; hence perfect matching between the experimental and numerical combustion for SPC was not attained. Nevertheless, by optimizing the injection timing to resemble the phasing of experimental Heat Release Rate (HRR) curve, to the “best extent possible”, more premixing, higher rate of penetration, and less rich-mixture mass was observed.
Heavy-duty engines must meet strict emission standards and retain high fuel efficiency. This thesis examines a new type of fuel injector nozzle for a pilot-ignited direct-injection natural gas engine. The nozzle uses paired jets that increase mixing with air during combustion, which aims to reduce the amount of particulate matter (PM) formed. Tests were performed for different speeds and loads and over engine parameter sweeps (including timing, EGR, EQR, and diesel pilot mass) to compare the effects on the emissions to a single-hole nozzle. Low-PM strategies and morphology of the soot were compared as well.Contrary to expectations, the tests showed large increases in CO and PM from all the paired nozzles at all modes compared to the single-holed injector. Changing speed and load did not affect the relative emissions so further tests were only done with the paired nozzle that had the least emissions.The engine parameter sweeps at mid speed, high load (B75) showed similar emission patterns for the paired-hole nozzle and the single-hole nozzle. This suggests that the reasons for the high emissions lie in the characteristics of the jets, which are not changed much under normal HPDI operation.Injecting the natural gas before the pilot injection reduced PM. Late post-injection of some of the gas reduced PM by 50% without increasing other emissions for both injector types. Apparently, these strategies could work for other HPDI injectors.Compared to the reference injector, the paired-hole nozzle produced larger soot aggregates and larger numbers of particles but soot primary particle size showed different trends at different conditions. Soot fractal dimensions were the same and consistent with conventional diesel soot.CFD simulations showed that fuel packets moved through a richer high PM and CO forming zone during combustion for the paired nozzle. This high sooting zone had to be avoided either by further mixing or less mixing to avoid the high emissions produced.The results presented here were developed on a single-cylinder engine. While trends are expected to be similar to those from an equivalent multi-cylinder engine, emission levels and fuel consumption are not directly comparable to production multi-cylinder engines.
Stringent regulations have been enacted to reduce particulate matter (PM) emissions from heavy-duty compression-ignition (CI) engines. New regulations (Euro VI) restrict PM mass and particle number concentration. To help meet these regulations, a greater understanding of the physical and chemical characteristics of the PM is desired. This thesis is concerned with the mobility, morphology (by electron microscopy), mass (filter sampling), light scattering and semivolatile content of the particles.Natural gas has become an increasingly attractive transportation fuel for both environmental and economic reasons. One technology to utilize gaseous fuels in heavy-duty engines is Westport Innovations Inc.’s High Pressure Direct Injection (HPDI™) system. This is a system where the natural gas is directly injected late in the compression stroke and ignition of the natural gas is provided by a diesel pilot.PM emissions were characterized from a heavy-duty Cummins ISX engine converted to single cylinder operation and operating under HPDI™ fueling. Tests were performed to observe the effects of speed and load combinations, the effects of operating parameter variations (Injection timing, equivalence ratio, gas supply pressure, EGR % and diesel injection mass) and the effects of fuel premixing on the PM emissions.Engine load was more important than speed for qualitatively grouping the PM emission characteristics (mass, number, semi-volatile fraction). The exception is at low engine speeds where low mass and number concentrations were observed, along with nearly constant particle sizes, across different loads.The effects of the input parameter variations were analyzed with response surface methods. The PM emissions were more sensitive to changes in the input parameters than the gaseous emissions. Equivalence ratio, engine power and injection pressure were the most important parameters for PM mass emissions. Overall, the PM emissions varied monotonically with the input parameters and no local PM emission minima were observed.Partially premixing some of the natural gas before ignition can reduce PM emissions by over 80% at some conditions at the expense of cycle-to-cycle variability and pressure rise rates. Some optimized equivalence ratios and EGR percentages were developed to improve the stability of combustion.
A mathematical model which estimates spatial infection risk as a function of pulmonary rate and deposition region has been developed based on the does-response model. It is specifically designed for enclosed space with consideration of pathogen bio-properties, such as viability and infectivity.Firstly, eleven cases of Tuberculosis (TB) outbreaks in aircraft are studied to develop the optimal parameters set. It is then used to perform model validation and investigation of sample inpatient room spatial infection risk. Secondly, infection risk for eleven TB outbreaks are compared with modeling and Wells-Riley estimations. As a result, modeling results are within the calculated range of Wells-Riley prediction. To determine the importance of viability and ventilation rate regarding HVAC system design for health facilities, infection risks are calculated at different viability and ventilation rates. Based on the observation, ventilation rate or particle concentration in the space dominate the infection risk distribution, except when viability decays extreme rapidly. Thirdly, the spatial infection risk is investigated for TB in a typical 60 m³ inpatient room with displacement and well-mixed ventilation systems. Two room settings, a nurse standing close to the patient’s bed versus a visitor standing far away from the bed, and two coughing directions, horizontal versus vertical, are studied. The results show that for coughing horizontally, when the nurse stands beside the patient's bed, his/her breathing zone is the highest risk zone for displacement ventilation. Under displacement ventilation, the infection risk is lower when visitor stands away from the bed compared to stand close to the bed if the visitor is the only person present in the room besides the patient. The infection risk of the breathing zones in the two cases with horizontal coughing are both higher than 25%. However, when a patient coughs vertically, the displacement ventilation significantly reduces the infection risk. With 24 hours exposure, the infection risk for the nurse and the visitor are both less than 5%.
Billions of people worldwide use biomass fires or cookstoves on a daily basis, with significant resultantcontributions to emissions of global carbonaceous aerosols. The use of biomass as a fuel has an impact on localecosystems, contributes to CO2 levels in the atmosphere, and black carbon (BC) and organic carbon (OC) affect theearth’s radiative balance. Widespread initiatives, including carbon funding programs, propose to replace traditional“three-stone” open fires with “improved” cookstoves designed to reduce fuel usage. While numerous studiesinvestigate cookstove efficiency and publish emissions factors for gaseous pollutants and overall particulate matter(PM), there is a lack of focus on the size and nature of ultrafine particulate (UFP) emissions. This paper comparesultrafine emissions during steady combustion from a traditional three-stone fire and two improved stoves: a Rocketstove (“Chulika”) and a Gasifier stove (“Oorja”).An AVL emissions bench measured gaseous products. PM instrumentation included a TSI SMPS, TSI APS, TSIDustTrak DRX, Magee Scientific Aethalometer, and 47mm PTFE and quartz filters; a thermophoretic samplingdevice was employed to gather material for PM imaging using transmission electron microscopy (TEM).The improved cookstoves demonstrated high combustion efficiency compared to the three-stone fire and are likelyto reduce biomass consumption. Additionally, emitted PM mass was reduced by a significant amount. PMemissions from improved stoves had a higher proportion of BC compared with total PM, though there was relativelylittle variation in overall BC levels. The reduction in highly scattering OC that would accompany a large-scale shifttowards usage of improved stoves could affect the earth’s radiative balance, but this merits investigation withconsideration to other particle characteristics. Primary particles emitted from the improved stoves were smaller thanthose from the three-stone fire and appeared slightly less likely to coagulate into chain agglomerates. The observedshift towards greater quantities of smaller nanometer-sized particles could pose health concerns and is a point forfurther consideration by health scientists and reinforces the need for adequate ventilation for all cookstoves,independent of type.
Time-Resolved Laser-Induced Incandescence (TR-LII) uses a high-energy laser pulse to detect airborne soot particles. When a laser pulse encounters a light-absorbing particle, the energy will be absorbed, resulting in an increase in temperature. If the temperature is high enough, incandescence can be used to quantity of the soot mass (EC). TR-LII tracks the incandescent light as the particle cools, providing information on the particle structure. It is a common in LII research to assume that the soot aggregate particles contain only Elemental Carbon (EC) and if these soot aggregate particles are internally mixed with Organic Carbon (OC), the intense energy from the laser beam evaporates the OC instantly. Unfortunately, these assumptions are inaccurate because the existence of OC will alter the structure and heat transfer properties of the aggregate. The existence of OC also has an effect on the energy absorption by the soot particulates. An experiment was conducted using India ink particles as a soot surrogate and Oleyl Alcohol as a model OC coating. The experiment’s objective is to study the effect of coating (OC) on the LII detection. The coating increased the peak temperature, but the apparent primary particle diameter decreased when more coating was introduced, whereas the main output variable (volume fraction) showed a mixed response. Up until a thickness of 40 nm, the apparent volume fraction value was declining, but for a thicker coating condition, the value was increasing. Another experiment was conducted to study the effect of the coating on the particulate distribution downstream of the laser heating in the LII detecting chamber. The soot fragmentation phenomenon was found to occur in the LII system and the existence of coating has an effect on the soot fragmentation phenomenon. Compared to uncoated particle, which produces small fragments (
Generation IV CANDU Supercritical Water Reactor (SCWR) is being developed to use a light water coolant at high temperature and pressure beyond the critical point of water (374⁰C and 22.1 MPa). The dramatic decrease in the solubility of magnetite in supercritical water suggests that the precipitation of magnetite particles will occur in the reactor core which can deposit on the fuel cladding or be transported to the steam turbine. A once-through flow system was modified to develop experimental techniques for studying the deposition and transport of magnetite particles in supercritical water onto stainless steel 316L. Experiments were run with temperatures ranging from 200°C to 400°C and a pressure of 23.7 MPa. A hydrothermal method for synthesizing magnetite particles was adapted for producing simulated corrosion products in which a typical run had an iron concentration of 0.005 mol/L and lasted for 40 minutes. An online monitoring technique using thermal resistance to infer deposit loadings showed deposition and removal cycles of the corrosion product on the tube wall. Scanning electron microscope images of particles on the tube inner wall and those collected by the high temperature, high pressure filters revealed magnetite particles which were several hundred nanometers to several microns in diameter depending on the precursor and condition of the system. Ultrasound and acid wash cleaning methods were used to remove deposits from the test section for determining deposit thickness and adhesive strength. The strength of deposit adhesion was observed to increase along the tube, particularly under supercritical conditions suggesting precipitation of dissolved species may enhance the strength of the deposit. By comparing the results, a comprehensive approach was developed to study magnetite fouling in supercritical water conditions. Finally, comparison between a simulation model based on mass transport equations and experimental deposition suggests that mass transport alone can overestimate the deposition thickness when surface attachment and removal are significant as they were for many experiments in this study. The simulation predicted as an upper limit scenario that fouling in a CANDU SCWR could increase the fuel cladding temperature at certain locations by up to 23.9⁰C after one year of operation.
Spark-ignited engines are known to produce PM composed of solid, volatile or semi-volatile particles including spheres of carbon soot formed into agglomerates, other forms of carbonaceous particles, metal particles and charred droplets of engine oil. In this thesis, detailed observation has revealed that SI PM is partly composed of fully-formed carbon nanotubes and fullerenes in addition to known particle types previously presented in the literature. The purpose of this work is to ascertain the shape and size of particulate matter being emitted by SI engines. In this thesis, PM thermophoretic sampling and transmission electron microscopy were used to collect and analyze engine soot samples, respectively. Furthermore, the operation of the thermophoretic sampling device used in engine PM sample collection was characterized to identify the sampling efficiency based on particle deposition and sampling biases based on differences in particle thermoconductivity for various forms of carbon such as turbostratic soot, crystalline carbon nanotubes and calcium. In general, the efficiency of the TPS method was roughly estimated to be 30-80% efficient based on experimental results.In this thesis, carbon nanotubes and fullerenes have been identified as being emitted from in-use, spark-ignited natural gas and gasoline burning auto-rickshaw engines tested in New Delhi, India. Emission of fullerenes and CNTs was on the order of 10% +/- 7% of the non-volatile particulate matter. Agglomerates, dense spherical particles believed to be charred engine oil, and unidentified or compound particles were also cataloged. Confirmation that nanotubes are being produced by SI engines was achieved using PM samples collected from the Ricardo Hydra laboratory test engine at the University of British Columbia, Clean Energy Research Centre. Under more controlled conditions than can be achieved sampling in-use vehicles, SI engine PM is found to be a complex collection of dense, dark (possibly charred oil) spheres, small primary particle agglomerates, small particle deposits, volatile droplets, carbon nanotubes and fullerenes and large ‘other’ particles. High resolution TEM confirmed tube-shaped particles to be fully formed multi-walled carbon nanotubes.
High-pressure direct-injection of natural gas for use in compression-ignition engines has been found to reduce emissions without sacrificing performance relative to pure diesel operation. In the present work, prototype ‘co-injectors’ which inject a diesel and natural gas mixture from a single injector were tested in a heavy-duty, 6-cylinder Cummins ISX engine with 5 cylinders disabled. One prototype (‘B’) was tested under low-speed, low-load conditions, to determine the effects of fuel flows and in-cylinder conditions on the combustion characteristics of co-injection. Co-injector B, and a second prototype (Co-injector CS: A variation of Co-injector B which mixes the fuels differently) were tested at three engine modes using two injections per cycle to determine the effect of the duration of the first injection on emissions and combustion characteristics. The performance of the co-injectors was compared to Westport Innovation’s High Pressure Direct Injection (HPDI) J36 injector to determine if co-injection can produce comparable emissions.Single injection tests carried out with Co-injector B at 800 RPM over a range of diesel flows, gas flows, injection pressures, and cylinder temperatures & pressures were used to generate response surfaces for knock intensity, ignition delay, and combustion efficiency. It was found that diesel flow and the cylinder pressure at the time of injection had the largest effect of knock intensity and ignition delay, and that the knock/ignition delay relationship in co-injection is inverse. The double injection tests showed that the difference in diesel distributions within the gas plenums of CS and B results in more diesel being injected during the first injection in CS compared to B, which supports previous results. It was found that short first pulses resulted in the lowest emissions for both co-injectors, and that with low first gas pulse widths the performance of the co-injectors is comparable to that of Westport’s HPDI-J36 injector.
Natural gas has a high auto-ignition temperature, therefore natural gas engines use anignition source to promote combustion. The high-pressure direction-injection (HPDI)systems available use small diesel injections prior to the main gas injection. A new seriesof HPDI injectors have been developed that inject diesel and gas simultaneously throughthe same holes. In order to understand and control injection and combustion behavior inan engine, it is essential to understand how injection mass is related to the diesel/gas ratioand injection command parameters.Three prototype injectors are examined. “Prototype B” most closely resembles a standardJ36 HPDI injector, but has a modified diesel needle that injects diesel internally into acommon diesel/gas reservoir. Prototypes “CS & CSX” have the diesel needle eliminatedand replaced with a flow restrictor. The pressure difference between the diesel and thegas controls the quantity of diesel injected. A single pulse width (GPW) for the gasneedle controls the fuel quantities.An injection visualization chamber (IVC) was developed for flow measurements andoptical characterization of injections into a chamber at pressures up to 80 bar. Diesel andnatural gas are replaced by VISCOR® and nitrogen to study non-reacting flows. A novelfeature of the IVC is a retracting shroud that allows the injector to reach steady-state priorto imaging.For low commanded injection duration (GPW less than 0.60 ms), the relation betweenGPW and injected mass is non-linear, for all injectors tested. For gas pulse widths greaterthan 0.65 ms the Co-injectors exhibit approximately linear behavior with higher dieselfuelling quantities lowering gas flow quantities. All Co-injectors are compared tobaseline gas flow quantities of a standard J36 to show design difference effects on flowquantities. The sensitivity of gas flow to diesel in injection quantities, as well as thedischarge coefficient are computed and theoretically modeled for each prototype. Resultssuggest differing diesel/gas distributions, dependent on method of diesel introduction andactuator response.Imaging indicates the mechanical delay of the injectors is independent of chamberbackpressure but dependent on fuel supply pressure. However, gas injection quantitiesare increased by higher chamber backpressure. Changes in the gas/liquid ratio arereflected in different jet image characteristics. These results are compared to theory usingan AMESim model developed for an existing production injector.