Experimental characterisation of swirl stabilized annular stratified flames

A burner for investigating lean stratified premixed flames propagating in intense isotropic turbulence has been developed. Lean pre-mixtures of methane at different equivalence ratios are divided between two concentric co-flows to obtain annular stratification. Turbulence generators are used to control the level of turbulence intensity in the oncoming flow. A third annular weakly swirling air flow provides the flame stabilization mechanism. A fundamental characteristic is that flame stabilization does not rely on flow recirculation. The flames are maintained at a position where the local mass flux balances the burning rate, the result is a freely propagating turbulent flame front. The absence of physical surfaces in the vicinity of the flame provides free access for laser diagnostics. Stereoscopic Planar Image Velocimetry (SPIV) has been applied to obtain the three components of the instantaneous velocity vectors on a vertical plane above the burner outlet where the flames propagate. The instantaneous temperature fields have been determined through Laser Induced Rayleigh (LIRay) scattering. Planar Laser Induced Fluorescence (PLIF) on acetone has been used to calculate the average equivalence ratio distributions. Instantaneous turbulent burning velocities have been extracted from SPIV results, while flame curvature and flame thermal thickness values have been calculated using the instantaneous temperature fields. The probability distributions of these quantities have been compared considering the separate influence of equivalence ratio stratification and turbulence. It has been observed that increased levels of turbulence determine higher turbulent burning velocities and flame front wrinkling. Flames characterized by stronger fuel stratification showed higher values in turbulent burning velocities. From the curvature analysis emerged that increased fuel concentration gradients favour flame wrinkling, especially when associated with positive small radius of curvature. This determines an increased surface area available for reaction that promotes a faster propagation of the flame front in the oncoming combustible mixtures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The development of a combustion temperature standard for the calibration of optical diagnostic techniques

This thesis describes the development and evaluation of a high-temperature combustion standard. This comprises a McKenna burner premixed flame, together with a full assessment of its temperature, stability and reproducibility. I have evaluated three techniques for high-accuracy flame thermometry: Modulated Emission in Gases (MEG), Rayleigh scattering thermometry and photo-acoustic thermometry. MEG: Analysis shows that MEG is not usable in this application because the sharp spectral features of the absorption coefficient of gases are represented within MEG theory as an average absorption coefficient over the optical detection bandwidth. A secondary difficulty arises from the lack of high power lasers operating at wavelengths that coincides with molecular absorption lines in the hot gas. Rayleigh Scattering: Applying corrections for the temperature-dependence of the scattering cross-section, it has been possible to determine the temperature of the combustion standard with an uncertainty of approximately 1%. The temperature dependence of the scattering cross-section arises from changes in the mean molecular polarisability and anisotropy and can amount to 2% between flame and room temperatures. Using a pulse Nd-YAG laser operating at 532 nm and high linearity silicon detectors, the Rayleigh scattering experimental system has been optimised. Temperatures measured over a three-month interval are shown to be reproducible to better than 0.4% demonstrating the suitability of the McKenna burner as a combustion standard. Photo-Acoustic: By measuring the transit time of a spark-induced sound wave past two parallel probe beams, the temperature has been determined with an uncertainty of approximate 1%. Flame temperatures measured by the photo-acoustic and Rayleigh scattering thermometry system show good agreement. For high airflow rates the agreement is better than 1% of temperature, but for low airflow rates, photo-acoustic temperatures are approximately 3.6% higher than the Rayleigh temperatures. Further work is needed to understand this discrepancy.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A study of laser-induced incandescence under high vacuum conditions

Laser-Induced Incandescence (LII) occurs when a high-energy pulsed laser beam encounters graphitic particulate matter particles like soot or carbon black. The particles absorb laser energy from the beam and see an increase in their internal energy, resulting in an increase of temperature. At the same time, the particles loose energy through heat transfer mechanisms. If the energy absorption rate is sufficiently high, particle temperature will rise to levels where significant incandescence (blackbody emission) can occur .Typically, Laser-Induced Incandescence produces 50ns to 1μs long light pulses at atmospheric pressure. So far, LII measurements had been restrained to conduction-dominated conditions, whereby signals are short-lived (less than one microsecond) and require sensitive nanosecond resolution instrumentation. This thesis introduces a novel LII – based measurement method performed under high vacuum conditions. The novelty of LII under vacuum resided in the fact that heat conduction away from the soot particle becomes negligible below 10-2 mbar and this constituted a step away from the typical situation, whereby laser absorption is followed by heat conduction from the particles to the surrounding medium. Instead, sublimation and radiative heat transfer would follow laser absorption. The consequence was the obtention of long-lived LII signals (up to 100 microseconds) and a large gain of photons (ranging between 50 to 300) emitted per primary soot particle during LII temperature decays. Furthermore, the refractive index function E(m) value could be determined directly from measured radiative temperature decays, with potentially an uncertainty of circa 7%, which outperformed current soot extinction measurements. In addition, for laser fluences below 0.06 J/cm2, a regime where only laser energy absorption and radiative heat transfer apply would be reached and LII signals became independent of particle size. Throughout this project, Laser-Induced Incandescence under vacuum was applied to a sample of carbon powder (agglomerated soot particles) sealed in a glass vessel and held below 10-3 mbar. Initial spectral measurements performed at a laser fluence of 0.3 J/cm2 confirmed the obtention of long-lived (60 microseconds long) blackbody spectra, which confirmed the feasibility of the technique and yielded an E(m) measurement of between 0.35 and 0.45. A second study was performed with a dualwavelength pyrometric system specifically designed for recording live LII temperatures and signal intensities coupled to an absolute light intensity calibrated intensified imaging system. Experimental results unveiled the thermo-physical behaviours of agglomerates enduring LII. The most remarkable outcomes of the results concerning carbon nanoparticles agglomerates were that: clusterous particulate matter absorbs and radiates light in a very similarly to single isolated carbon nanoparticles and therefore obey largely the Rayleigh limit; soot agglomerates also dissociate during LII in an explosive mode and ejecta were measured to reach up to 400 m/s following chain dissociations; complete agglomerate dissociations can be obtained and measurements performed on individual aggregates of primary soot nanoparticles. In parallel, LII measurements revealed that optical shielding is largely present within agglomerates, and therefore clusters dissociations exposed large quantities of particulate matter and increased greatly LII signal levels. Overall, radiative heat transfer measurements yielded E(m) = 0.4 to 0.6 and time-integrated ICCD measurements resolved signal levels as low as groups of 6 carbon nanoparticles. This sensitivity clearly was the highest recorded to date for Laser Induced Incandescence and the sensitivity boundary of the technique was increased to nearly resolving single nanoparticles. Further measurements were performed in collaboration with the National Research Council (NRC) of Ottawa, Canada, at the Combustion Research Group facility. The results obtained validated the obtention of repeatable temperature profiles for Laser- Induced Incandescence under vacuum. In addition, comparison between results obtained on a controlled source of agglomerates at atmospheric pressure established that the increase for LII signals with laser fluence for both atmospheric and vacuum conditions could be directly associated with agglomerates dissociations. Indeed, net diminutions in optical shielding were measured in both conditions and could be coupled with diminutions in thermal shielding at atmospheric pressures. Highresolution temperature measurements established that laser absorption, annealing, sublimation and radiative heat transfer rates could be unprecedently and directly measured by laser-induced incandescence under vacuum. Annealing and sublimation of soot primary particles could also reasonably be assumed to be the phenomena at the heart of agglomerate dissociations. It was also established that agglomerate dissociation was dependent not only on laser fluence but also on the instantaneous laser power absorbed by the carbon agglomerates: indeed measurements performed at NRC were effected with a instantaneous laser powers four times lower than previously and radiative heat transfer measurements attested incomplete agglomerate dissociations with E(m) values measured between 0.8 and 1. Overall, the present work introduces LII under vacuum as a high sensitivity measurement method for particulate matter. The sensitivities obtained approached nanoparticles resolution and constitutes one of the most sensitive particulate matter measurement technique to date with real-time measurements capability. Because of the sample studied, agglomerate dynamics during LII were unveiled for the first time and explained the increase of LII signals with laser fluence as a diminution of both thermal and optical shielding. The LII under vacuum technique also proved its ability to resolve and isolate some of the key phenomena occurring during LII: laser absorption, annealing, sublimation and heat radiation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Study of fuel injection and mixture formation for a gasoline direct injection engine

Future requirements for lower automotive emissions have lead to the development of new internal combustion (IC) engine technologies. Gasoline Direct Injection (GDI), for example, is one of these promising new IC engine concepts. It offers the opportunity of increased efficiency through unthrottled operation. However, the realisation of this concept is critically dependent on the in-cylinder mixture formation, especially in the late injection/lean operation mode. Ideally, this would require a precise stratification of the in-cylinder fuel-air mixture in 3 distinct zones: an ignitable pocket located at the spark plug, surrounded by a stoichiometric mixture of fuel and air, encompassed by air. To enable this stratification, the GDI concept utilises advanced injector technology. Phase Doppler Anemometry (PDA), Planar Laser-Induced Fluorescence (PLIF) and the combination of PLIF and Mie scattering in the Laser-Sheet Dropsizing (LSD) technique, have been applied to sprays in the past to obtain dropsize information and study the mixture formation process. These new GDI sprays are denser, their droplet sizes are smaller and they evaporate faster, and as such, place us at the limit of the validity of these measurements techniques. The diagnostics were applied to a GDI spray in a pressure vessel for realistic in-cylinder conditions, ranging from supercooled to superheated environments. Tracer evaporation issues in the PLIF technique were resolved by using a dual tracer system. The study showed that the LSD technique provided good quantitative data in low evaporation regimes. In highly evaporating regimes, the technique still gave reliable dropsize data for the early stages of the injection, but was limited afterwards by vapour-phase contribution to the fluorescence signal. Variations between PDA data and LSD results also suggested a deviation of the Mie scattering signal from the assumed d2 dependence. This was further investigated and was found to be true for small droplets (d/?. <0.2). This source of error might be improved by using a different observation angle. High density seriously compromises the accuracy of PDA, whilst its effect through multiple scattering is of second order for the LSD technique. In low evaporating regimes, LSD has the overall advantage of being a 2-D measurement technique, and will yield data with a maximum error of 30% in dense parts of the spray where PDA data is totally unreliable. If the spray evaporates quickly, PLIF by itself is an appropriate tool for following the air-fuel mixture, because short droplet lifetimes limit the 2-phase flow behaviour of the spray. Particle Image Velocimetry (PIV), the LSD technique and equivalence ratio LIF measurements were applied to a BMW single cylinder optical GDI engine. The early injection operation showed no particular issues. However, the results obtained in the late injection highlighted the poor mixing and inappropriate stratification.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of a spark plug fuel injector for direct injection of natural gas in spark ignition engine

The use of methane in spark ignition engines is mainly due to its cleaner emissions and relatively low price. However, when methane replaces gasoline in the externally mixing carburettor or port injection engine, power is reduced and upper speed is limited. These are because the burning velocity of methane is slower than of gasoline, and some air is displaced in the intake manifold in order to compensate the low density methane. The problem can be mitigated when fuel is directly injected into the combustion chamber after the intake valve closes. This results in an increased volumetric efficiency, a higher absolute heating value of mixture and a faster burning rate. The work presented in this thesis aims to develop a conversion system that enables methane to be directly injected into the combustion chamber of a spark ignition engine without modifying the original structure of the engine. The system, named as Spark Plug Fuel Injector (SPFI) combines a fuel injector with a spark plug. A fuel path is drawn along the periphery of the spark plug body to deliver the injected fuel to the combustion chamber. The system was installed and tested on a Ricardo E6 single cylinder engine with compression ratio of 10.5: 1. Cylinder pressures were taken as the main indicator of the engine performance and selected indicated performance were presented. A set of port injected data for the engine running on methane was also taken in order to provide a comparison of performance with SPFI direct injection. Results show that the indicated performance of the SPFI methane direct injection at the tested speed was lower than the optimised methane port injection operation. This was mainly due to the quality of air-fuel mixing, which is a result of spatial and temporal limitation of direct injection operation. Flow visualization using the PLIF method shows that even though sufficient gas jet penetration from SPFI injection nozzle was achieved, the cone angle was very narrow. The conclusion from imaging experiments implies poor mixing, hence the performance suffers drawback. However, with direct injection, volumetric efficiency is increased ands combustion duration is faster. These two factors are desirable for engine performance improvement. SPFI has proven to be a practical and low cost conversion to methane. Even though the performance is lower than port injection, its benefits are significant. As the SPFI design is simple and requires no modification to the original structure of the converted engine.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Measurement and analysis of rally car dynamics at high attitude angles

This research aims to investigate the nature of high β-angle cornering as seen in rallying and in particular the World Rally Championship. This is achieved through a combination of sensor development, on-car measurement and vehicle dynamic simulation. Through the development of novel β-angle measurement technology it has become possible to measure and study vehicle attitude dynamics on loose gravel surfaces. Using this sensor, an understanding of how a rally driver uses the dynamics of the vehicle and surface to maximise performance has been obtained. By combining the new data stream with accepted vehicle dynamic theory, the tyres have been considered and general trends in gravel tyre performance unveiled. Through feedback, these trends have been implemented as a means of tuning a dynamic model to improve realism and permit an analysis of cornering trends in rally cars. Active control systems have been considered that could implement more sophisticated algorithms based on this understanding and potentially use the new sensor information as an input signal. A case study which explores such a possibility is included.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Heat and mass transfer behaviours of building materials and structures

Heat storage as a means to respond to the requirements for improved energy efficiency motivated this study. The objective was to evaluate the impact of thermal energy storage systems in dwellings under Mexican climatic conditions. In the first part of this work thermal behaviors of adobe traditional architecture is discussed; in the second part a latent heat storage system using phase change materials (PCMs) is proposed and assessed. The high thermal mass structural elements of adobe traditional architecture have been charactefted as heat wave modulators. Nevertheless, the moisture content in these structures also plays a significant role as a means for heat storage and potentially enhancing thermal lag. The objective of this part of the study was to assess the scope of existing coupled heat and mass transport models regarding water contained latent heat storage on porous structures. The significant contribution of latent heat storage recognized in adobe structures, led to the study of a solar-thermal storage system using (PCMs). The objective of this part of the study was twofold: 1) Enhance the existing computational models on the Stephan problem by considering the effect of regional variations (weather conditions imposed) on the boundary conditions. 2) Evaluate the impact of the solar-thermal system proposed when applied in dwellings in view of regional variations under Mexican weather conditions. Solar-thermal storage systems independent of the structure offer the possibility to be applied to existing buildings as well as new constructions. The proposal is a storage element that constitutes internal blinds in windows. The computational model of the Stephan problem was solved with the enthalpy method. Simulations were run under different sets of climatic conditions. For the first time the main factors for promoting system's optimisation, when gathered in a single comparison study, provided a more general insight on system's performance. Experimental work was also carried out regarding the charging of the heat storage unit by heat gains other than direct radiation, and the storage unit's performance as insulator. A large-scale solar simulator was constructed. Statistical analysis of experimental results showed interesting findings including: The important role that internal heat gains play on the charging of the latent heat storage unit proposed. A larger effect on the discharging ratio was found with lower air temperatures than with faster air flow rates. The faster discharging rate tests also released slightly more energy. PCM volume was found to be the most critical factor on system performance. The importance of providing the means to discharge the total quantity of heat stored was pointed out. For the cooling mode, elements to enhance discharging might be required. For system control, thermal insulation was found to be an effective measure when the discharging is required to occur over a longer period. The multiple PCM unit was found to be more efficient during the charging process (storing more energy) than units containing a single PCM. Nevertheless the single PCM unit performed better for cooling than the multiple PCM unit. The question was raised as to what extent PCM thermal conductivity actually influences system's performance. The thermal storage system proposed in this study reduced the heating system energy consumption requirements for an experimental room by 28.6%.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Wandering as a sociomaterial practice : extending the theorization of GPS tracking in cognitive impairment

Electronic tracking through global positioning systems (GPSs) is used to monitor people with cognitive impairment who “wander” outside the home. This ethnographic study explored how GPS-monitored wandering was experienced by individuals, lay carers, and professional staff. Seven in-depth case studies revealed that wandering was often an enjoyable and worthwhile activity and helped deal with uncertainty and threats to identity. In what were typically very complex care contexts, GPS devices were useful to the extent that they aligned with a wider sociomaterial care network that included lay carers, call centers, and health and social care professionals. In this context, “safe” wandering was a collaborative accomplishment that depended on the technology’s materiality, affordances, and aesthetic properties; a distributed knowledge of the individual and the places they wandered through, and a collective and dynamic interpretation of risk. Implications for design and delivery of GPS devices and services for cognitive impairment are discussed

A retrospective review of oral low-dose sirolimus (rapamycin) for the treatment of active uveitis

Purpose: The purpose of this study is to elicit the role of oral low-dose sirolimus as a corticosteriod-sparing agent for active uveitis. Methods: A retrospective, interventional case series was performed by reviewing the clinical records of all patients treated with oral, low-dose sirolimus (1-4 mg daily) for severe uveitis. Data reviewed included symptomatic improvement, Snellen best-corrected visual acuity, corticosteroid requirement, sirolimus levels, intraocular inflammation, spectral-domain optical coherence tomography, and fluorescein angiogram. Primary outcome measures were determined by the ability to decrease the intraocular inflammation, corticosteroid requirement, and frequency of flares. Results: Eight patients with varied diagnoses were treated with oral low-dose sirolimus for severe, chronic uveitis between 2008 and 2010. In four of the eight patients, there was an improvement of all primary outcome measures. While sirolimus monotherapy was successful in only one patient, a sirolimus/methotrexate combination was successful in three patients. Although there was a good initial response in three patients, treatment was a failure after serious side effects forced the cessation of sirolimus therapy. One patient was lost to follow-up. Conclusion: Sirolimus may have a limited role in severe uveitis as an adjunct corticosteroid-sparing agent in combination with more standard immunosuppressive agents. Oral low-dose sirolimus appeared to be better tolerated than higher doses, but there were a significant number of adverse events, requiring therapy to be stopped. © 2010 The Author(s)

Social-ecological connections across land, water, and sea demand a reprioritization of environmental management

Despite many sectors of society striving for sustainability in environmental management, humans often fail to identify and act on the connections and processes responsible for social-ecological tipping points. Part of the problem is the fracturing of environmental management and social-ecological research into ecosystem domains (land, freshwater, and sea), each with different scales and resolution of data acquisition and distinct management approaches. We present a perspective on the social-ecological connections across ecosystem domains that emphasize the need for management reprioritization to effectively connect these domains. We identify critical nexus points related to the drivers of tipping points, scales of governance, and the spatial and temporal dimensions of social-ecological processes. We combine real-world examples and a simple dynamic model to illustrate the implications of slow management responses to environmental impacts that traverse ecosystem domains. We end with guidance on management and research opportunities that arise from this cross-domain lens to foster greater opportunity to achieve environmental and sustainability goals.Peer reviewe