Browsing by Author "Greenhalgh, Douglas A."
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Item Open Access Characterisation of mixture preparation in lean premixed prevaporised combustor modules by planar laser fluorescence imaging and computational fluid dynamics modelling(2001-04) Davoudi, Henrik; Greenhalgh, Douglas A.In order to minimise the environmental impact of combustion emissions, radically new combustor concepts are under development. Lean premixed prevaporised (LPP) combustion has the greatest potential to achieve low emissions, particularly with respect to oxides of nitrogen. The role of fuel preparation is crucial in the success of the LPP combustor concept. Planar laser-induced fluorescence (PLIF) has been used to determine fuel placement and concentration, while computational fluid dynamics (CFD) has provided insight into the internal aerodynamics of two premixers. In order to determine the local equivalence ratios in a realistic device a calibration method, for the PLIF signal, has been derived. The vapour phase fluorescence of naphthalene, in the presence of oxygen, was calibrated against known conditions of temperatures and air-fuel ratios. This calibration was undertaken for an atmospheric and isothermal (non-combusting) flow. With regard to the small engine LPP module, PLIF measurements of the vapour fuel provided images of quantitative local equivalence ratios, at the exit of the premixer. In addition, based on the results of the liquid-phase measurements the evaporated fuel fraction was estimated. The computed droplet trajectories, within the premixing duct, highlighted the importance of the initial fuel dispersion from the injector. Two approaches were identified for improving the vaporisation and increasing the homogeneity of the air-fuel mixture. The large engine LPP module was investigated for several geometries and operating conditions. The evolution of the fuel dispersion, for those geometries, was characterised by PLIF images of the vapour fuel. In addition, the flame position inside the optical premixing duct was captured by video imaging for each geometry. 2D and 3D CFD simulations were performed to provide an insight into the aerodynamics of the premixer. These results were the basis of a schematic fuel jet breakup study, for two different injector configurations. Finally, the operational characteristics of this novel LPP module, featuring a conical centre-body, are discussed.Item Open Access Computational studies on HCCI engines.(Cranfield University, 2010) Correia, Eduardo Rodrigues; Greenhalgh, Douglas A.; Vaughn, Nick; Kelman, J.Emission legislation is changing in an effort to reduce exhaust emissions from the IC engines. Research and development has been focused on improving both spark-ignition and compression ignition engines to make them more efficient. Over the last decade, research has been increasing in Homogeneous Charge Compression Ignition (HCCI) engines. This alternative combustion process has the potential to combine the best of spark-ignition engines, namely the cleaner combustion with virtual no emission of NOx and soot, with the best of compression ignition, the increased engine efficiency with low fuel consumption and consequently lower carbon dioxide emissions. In this thesis, the effect upon HCCI combustion of different additives has been investigated. These additives can be used, to control the start of auto-ignition and/or to extend the load limits in which HCCI operation is possible. As part of this work, the HCCI combustion capability of running with different fuels was investigated. In order to study these effects on HCCI combustion, a detailed chemistry fuel oxidation mechanism was used together with a powerful chemical kinetic modelling tool, CHEMKIN. Simulations of the HCCI combustion were performed using a single-zone zero dimensional model and later a simpler multi-zone model comprising three different zones. Using the single-zone CHEMKIN model, additives influence on combustion was studied. From this study more complex mixtures were defined and more simulations were done, this time including different fuels such as ethanol, iso-octane and mixtures of both. A more complex model other than the single-zone tool available at CHEMKIN was developed and comparisons between the two simulation methods were performed. The results obtained from the simulations performed confirmed the fuel tolerance of HCCI combustion and the capability of running water diluted mixtures.Item Open Access The development of a combustion temperature standard for the calibration of optical diagnostic techniques(Cranfield University, 2005-11) Sutton, Gavin; Greenhalgh, Douglas A.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.Item Open Access Development of a spark plug fuel injector for direct injection of natural ags in spark ignition engine(Cranfield University, 2006-07) Mohamad, Taib Iskandar; Harrison, M. F.; Greenhalgh, Douglas A.In the name of God, The Most Gracious, The Most Merciful. By His will, this thesis has been completed as another episode of knowledge seeking and contribution. The author wishes to express a greatest gratitude to the academic supervisor for this project, Dr. Matthew Harrison and Professor Douglas Greenhalgh for their warmth, continuous guidance and support, priceless knowledge and expertise, and kindly understanding. Secondly, author's deepest appreciation to Dr. Mark Jermy, the initial supervisor for this project, for his ideas, understanding, support, availability and generosity for providing assistance both in author's academic and private life. To my mother and father whose supplications and encouragements have given me strength to complete this work. To my family whose support during this course of studies has given me comfort. To my parents in-law and siblings in-law, thank you for your support. My dearest gratitude to the beloved wife, Ira for standing by my side and giving me continuous support throughout this course of study and the hardship of life due to it. Your sacrifice is priceless. To my children, Balgis, Naufal, Nadiyah and Safiyah, you are my source of inspirations. A special thank to Dr. Glenn Sherwood, Tim Lee, Brian Scully, Richard Kennewell, Alan Hutching, and all others for providing technical supports during the experiment works. To Andreas, Eudoxios, Anni, Edouard, Fatiha, Alessio, Andy and Adam, I thank you all for the friendship and helps during my studies.Item Open Access Experimental and theoretical study of the two-phase flow inside a lean premixed prevaporised combustor(Cranfield University, 1999-09) Monmont, Franck; Greenhalgh, Douglas A.A experimental study of the two-phase flow inside a lean premixed prevaporised combustor has been carried out in order to evaluate the capabilities of large eddy simulations applied to engineering applications. To this end, a existing LPP design was modified in order to simplify the injection mechanisms involved and gain a optimum optical access if the critical injection region. The liquid and the gas phase inside the LPP module are then characterised with the help of non-invasive laser techniques, namely PDA for the liquid phase, LDA for the airstream and PLIF for the vapour phase. Relevant information regarding droplet sizes, droplet velocity, airstream velocity and fuel placement have thus been collected. The measurements are then evaluated against flow solutions computed by a Eulerian-Lagrangian ite-volume solver. A hybrid RANS/LES modelling strategy has been adopted for the gas phase and the Lagrangian tracking procedure has been updated to predict the influence of the gas turbulence on the droplet dispersion, and the heat penetrating the droplet during its evaporation. This simulation is finally matched against ZD and 3D steady RANS solution in a attempt to demonstrate the superiority of the time dependent approach.Item Open Access Experimental Characterisation of Swirl Stabilized Annular Stratified Flames(Cranfield University, 2007-01) Bonaldo, Alessio; Greenhalgh, Douglas A.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.Item Open Access Heat and mass transfer behaviours of building materials and structures(Cranfield University, 2005-03) Parra Saldivar, Maria Luisa; Batty, W. J.; Greenhalgh, Douglas A.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%.Item Open Access Investigation into mixing and combustion in an optical, lean, premixed, prevaporised combustor.(1996) Harding, Stephen C.; Greenhalgh, Douglas A.Gaseous and particulate emissions from combustion devices are implicated in many atmospheric environmental pollution concerns. Lean, premixed, prevaporised combustion is widely regarded as the most practical technique for reducing these emissions from gas turbine combustors to levels which will not cause significant environmental impact. This technique has been proved to be capable of reducing emissions of oxides of nitrogen to ultra low levels. However, further understanding and development is necessary before LPP combustors can be reliably fitted in production gas turbines. Particular problems are flashback and autoignition in the premixer and achieving a stable, lean primary zone. This thesis details a comprehensive series of measurements made upon a realistic LPP gas turbine combustor. The measurements elucidate the important, fundamental, physical processes which govern the performance of LPP combustors whilst providing a challenging and complete data set for CFD model validation. These measurements include data on the premixer velocity field, the fuel droplet size and velocities distributions, the fuel concentration in the premixer and primary zone and the combustion temperature. This has been interpreted to provide useful information such as the location and rates of fuel-air mixing, the proportion of temporal to spatial fluctuation in fuel concentration, the premixer swirl number, the flame brush thickness and the effect on mixing and placement of fuel fraction boiling point. It has been found that for mixing multi-component fuels in a duct, the rate of mixing and physical placement will depend on the boiling fraction of the fuel. High boiling point fractions evaporate later, experience longer droplet trajectories and mix much slower when compared to lower boiling fractions.Item Open Access An investigation into the characterisation of the laser-induced incandescence method for the measurement of soot in practical systems(Cranfield University, 2002-04) Grigorian, V.; Greenhalgh, Douglas A.The thesis describes the characterisation and application of the laser induced incandescence technique for making soot measurements in practical devices. Laser induced incandescence is the phenomenon whereby particulates such a soot absorb laser radiation and are heated to a temperature much higher than the bath gas. The broadband incandescence signal from the hot particles can be detected and the signal is proportional to volume fraction. The technique was used to study soot in partially premixed counterflow ethylene air flames, iso-octane explosion flames, and to image soot in a D. I. Diesel engine. Mie scattering, OH-LIF and absorption were used a complementary diagnostics. Appropriate ratios of LII and Mie images allowed the relative particle size and number density to be imaged. The counter flow burner measurements were used to study the effects of strain on soot formation while the bomb work demonstrated soot production in hydro-dynamically unstable cellular flames. The Diesel engine measurements are a demonstration of optical diagnostics in a real device. In order to characterise the LII signal behaviour two types of carbon aerosol generators were built. The liquid dispersion device produces almost spherical sub-micron carbon black particles. The device was used to characterise the soot field response, laser fluence response, signal decay and spectrum of the LII signal.Item Open Access Liquid jet instabilities in acoustically modulated crossflow(Cranfield University, 2005-06) Santos Nunez , C.; Greenhalgh, Douglas A.Combustion acoustic noise is a phenomenon which has attracted the attention of many people during centuries who observed the characteristics of singing flames in different conditions. It is only in recent years, with the advent of stringent environmental regulations to control combustion emissions that combustion instabilities have attracted new interest. This increasing interest is related to Lean Premixed Combustion, identified as the most promising technology for reducing NOx emissions, presents stability problems and combustion acoustic noise. Despite the adverse impact on noise and vibration affecting the combustor life, acoustic noise provokes an inefficient and unsteady combustion that generates environmental pollution. This work is related to the study of liquid jet injection under the actions of induced pressure oscillations as occurred in acoustic combustion noise. The main objective is to reproduce and analyse the coupling instability perturbations in a single liquid jet in crossflow. A test rig was design with an integrated pressure generator to produced fluctuations throughout the entire measurement range of interest. This pressure generator is a novel design that provides steady sinusoidal wave perturbations at low frequencies. Two different optical techniques were applied to measure the airflow velocity distribution as well as fuel distribution in response to the interacting acoustic oscillations. Alternatively, a mathematical model based on the laws of motion was developed to predict the jet trajectory and these predictions were compared to empirical correlations found in the literature. Empirical correlations were applied to predict the jet response and to extract relevant information with a parametric analysis. III The results show that, with the momentum flux ratio parameter that defines the jet penetration, droplet formation is governed by the time breakup. The phase lag, jet response and spray distribution are all sensitive to the magnitude of the airflow oscillations, having distinguished two groups of frequencies, crest and trough frequencies, which are related to a high and low pressure amplitude respectively.Item Open Access Measurement and analysis of rally car dynamics at high attitude angles(Cranfield University, 2006-05) Croft-White, Michael; Harrison, M. F.; Greenhalgh, Douglas A.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.Item Open Access Measurement and analysis of rally car dynamics at high attitude angles(Cranfield University, 2006-05) Croft-White, Michael; Harrison, M. F.; Greenhalgh, Douglas A.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.Item Open Access Study of fuel injection and mixture formation for a gasoline direct injection engine(Cranfield University, 2005-09) Reveille, T.; Greenhalgh, Douglas A.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.Item Open Access A study of laser-induced incandescence under high vacuum conditions(Cranfield University, 2006-07) Beyer, Vivien; Greenhalgh, Douglas A.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.Item Open Access A study of mixture formation in a lean burn research engine using laser fluorescence imaging(Cranfield University, 1996-05) Berckmuller, Martin; Greenhalgh, Douglas A.Lean burn in spark-ignition engines offers a significant efficiency advantage compared with stoichiometric operation. The lean operation is restricted by increasing cyclic fluctuation in torque. In order to make use of the efficiency advantage and meet the mandatory emission standards the lean operation limit has to be further extended. This requires particular control of the mixing of fuel and air. To study the effect of mixture formation on cyclic variability and to provide quantitative information on the mixing of air and fuel planar laser-induced fluorescence (PLIF) was developed and applied to an operating SI engine. The method is based on imaging the fluorescence of a fluorescent marker (3-pentanone) mixed with the fuel (iso-octane). 3-pentanone was found to have similar vaporisation characteristics to those of iso-octane as well as low absorption and suitable spectral properties. The technique was applied to an one-cylinder SI engine with a cylinder head configuration based on the Honda VTEC-E lean burn system. The mixture formation process during the inlet and compression stroke could be described by measuring the average fuel concentration in four planes, between 0.7 and 15.2 mm below the spark plug, in a section of the cylinder orthogonal to the cylinder axis. The results showed that for 4-valve pent-roof cylinder head systems with swirl inlet flows, fuel impinging on the cylinder wall opposite to the inlet valves has a major influence on the mixture formation process. In order to quantify the cyclic variability in the mixture formation process and its contribution to cyclic variability in combustion the fuel concentration in a plane near the spark plug was measured on a large number of cycles. It could be shown, that the fuel concentration in a small region close to the spark plug has a dominating effect on the subsequent pressure development for lean mixtures. Variations in the mixture concentration in the vicinity of the spark plug contribute significantly to cyclic variations in combustion. In order to address the issue of nonuniformity in residual gas concentration prior to ignition a laser induced fluorescence method was developed to measure nitric oxide (NO) concentrations in the unburned charge in the same one-cylinder research engine. Measurements of average and instantaneous NO concentrations revealed, that the residual gas is not homogeneously mixed with the air and that significant cyclic variations in the local residual gas concentration exist.Item Open Access A study of mixture formation in a lean burn research engine using laser fluorescence imaging(Cranfield University, 1996-05) Berkmuller , Martin; Greenhalgh, Douglas A.Lean burn in spark-ignition engines offers a significant efficiency advantage compared with stoichiometric operation. The lean operation is restricted by increasing cyclic fluctuation in torque. In order to make use of the efficiency advantage and meet the mandatory emission standards the lean operation limit has to be further extended. This requires particular control of the mixing of fuel and air. To study the effect of mixture formation on cyclic variability and to provide quantitative information on the mixing of air and fuel planar laser-induced fluorescence (PLIF) was developed and applied to an operating SI engine. The method is based on imaging the fluorescence of a fluorescent marker (3-pentanone) mixed with the fuel (iso-octane). 3-pentanone was found to have similar vaporisation characteristics to those of iso-octane as well as low absorption and suitable spectral properties. The technique was applied to an one-cylinder SI engine with a cylinder head configuration based on the Honda VTEC-E lean burn system. The mixture formation process during the inlet and compression stroke could be described by measuring the average fuel concentration in four planes, between 0.7 and 15.2 mm below the spark plug, in a section of the cylinder orthogonal to the cylinder axis. The results showed that for 4-valve pent-roof cylinder head systems with swirl inlet flows, fuel impinging on the cylinder wall opposite to the inlet valves has a major influence on the mixture formation process. In order to quantify the cyclic variability in the mixture formation process and its contribution to cyclic variability in combustion the fuel concentration in a plane near the spark plug was measured on a large number of cycles. It could be shown, that the fuel concentration in a small region close to the spark plug has a dominating effect on the subsequent pressure development for lean mixtures. Variations in the mixture concentration in the vicinity of the spark plug contribute significantly to cyclic variations in combustion. In order to address the issue of no uniformity in residual gas concentration prior to ignition a laser induced fluorescence method was developed to measure nitric oxide (NO) concentrations in the unburned charge in the same one-cylinder research engine. Measurements of average and instantaneous NO concentrations revealed, that the residual gas is not homogeneously mixed with the air and that significant cyclic variations in the local residual gas concentration exist.Item Open Access Study of Raman spectroscopy for the early detection and classification of malignancy in oesophageal tissue(Cranfield University, 2002-10) Kendall, Catherine; Greenhalgh, Douglas A.; Barr, H.; Stone, NicholasRaman Spectroscopy for the identification and classification of malignancy in the oesophagus has been demonstrated in this thesis. The potential of Raman spectroscopy in this field is twofold; as a adjunct for the pathologist and as a biopsy targeting tool at endoscopy. This study has demonstrated the feasibility of these potential applications in vitro. Spectral diagnostic models have been developed by correlating spectral information with histopathology. This is the current 'gold standard' diagnostic method for the identification of dysplasia, the established risk factor for the development of oesophageal cancer. Histopathology is a subjective assessment and widely acknowledged to have limitations. A more rigorous gold standard was therefore developed, as part of this study, using the consensus opinion of three independent expert pathologists to train the diagnostic models. Raman spectra have been measured from oesophageal tissue covering the full spectrum of malignant disease in the oesophagus, using a near infrared Raman spectrometer customised for tissue spectral measurements. Two spectral datasets were measured with different volumes of tissue probed using twenty and eighty times magnification ultra long working distance objectives. Multivariate statistical analysis has been used to extract the required spectral information with the greatest discriminative power. Principal component fed linear discriminant spectral models have been tested with leave one out cross validation procedures. Three pathology group models have correctly classified up to 91% of spectra, and eight group models have correctly classified up to 82% of spectra. Optimisation of the spectral models by selection of significant principal components, filtering the data and using staggered models was investigated. Effort has been made to understand the findings in their clinical context, with review of patient history and clinical progress, long term follow up is required. Preliminary work projecting independent data on to the models has been encouraging with 76% of the spectra in the three group model correctly classified, approaching classification levels of the training dataset. Formalin fixed tissue models were demonstrated to perform well, with 80% of the spectra were correctly classified in the seven group model. This further demonstrates the potential of Raman spectroscopy as a pathology tool. If Raman spectroscopy is to be implemented in a clinical setting it must be transferable between different measurement systems. This has been evaluated with oesophageal tissue spectra measured on two systems using three objectives. Simple calibration has demonstrated the use of multiple systems and measurement parameters in the development and application of spectral classification models. Testing of a new design of fibre probe has provided encouraging preliminary results. There is potential for the application of Raman spectroscopy in vivo, however the technology remains immature. Spectral maps of samples taken from across the spectrum of disease have shown clear delineation of the morphological features seen on the H&E images. Furthermore the biochemical information elicited has been analysed. Initial measurements of oesophageal tissue using multiphoton imaging have demonstrated the potential of collagen autofuorescence in the diagnosis of malignant change.Item Open Access Vector-scalar imaging in combustion using PIV and LIF(1995-12) Farrugia, N.; Greenhalgh, Douglas A.The effect of turbulent flow-fields on a premixed flame-front has been of considerable interest in the field of combustion research. Modern laser diagnostics allow the measurement of important parameters such as species concentration, temperature and flow velocity with an accuracy, resolution and rate of data acquisition that has not been available with physical probes. The ability to simultaneously gather data over a two or three-dimensional region permits powerful digital analysis of the fundamentals of combusting systems. The aim of this project was to demonstrate the possibility of combining twodimensional species concentration and velocity measurement techniques, in order investigate the interaction of a turbulent flow-field at a premixed flame-front. Digital Particle Image Velocimetry was investigated as a diagnostic for making velocity measurements in turbulent combustion environments. The standard monochromatic two-pulse technique produces a 180° ambiguity in the direction of each velocity vector. In order to resolve the velocity direction directly, a feature that would be important in combustion studies, a novel variation of PIV was developed. Three Pulse Digital PIV used three unequally spaced monochromatic laser pulses to code the flow direction into the images. A triple-correlation function extracted the correct flow direction and resulted in less vector drop-out, since noise correlations were greatly reduced. A complete analysis software package was written to extract the velocity information from both two and three pulse digital PIV images. The technique was tested on various cold flow, demonstrating its ability to resolve the flow direction. Planar Laser Induced Fluorescence was used to measure the concentration of the OH radical in turbulent premixed methane-air flames. Over four hundred experimental images were obtained and corrected for systematic errors. Fractal analysis of the flame-fronts in these images was used to extract the inner cut-off values, the smallest scale of wrinkling. The inner cut-off distributions were invariant with stoichiometry and maturity of flame. The maximum OH fluorescence signal at each point along a flame-front was used to give a measure of the local mass burning rate. Correlation of the reaction rate with flame curvature class revealed that convex regions had enhanced burning rates, while concave regions had suppressed burning rates. The two laser diagnostic techniques were combined in an experimental investigation of a triple flame in a counterflow burner. Joint PFF-velocity and joint OH-velocity images were generated, demonstrating the possibility of using the combination of PLEF and DPIV to study flame-turbulence interactions in premixed combustion.