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The gas turbine has been widely used for mechanical drive, electric power generation and jet propulsion. Challenged by strict CO2 emission regulations and competition between manufacturers, designers push the boundaries for an ever more efficient gas turbine. The cycle efficiency of the gas turbine is a crucial parameter that drives the engine performance and fuel burn. Improved cycle efficiency can be achieved by raising the turbine entry temperature, as well as the pressure ratio across the compressor. Today’s gas turbine engines use bypass cooling air from the high-pressure compressor, to cool down the seal disc cavities and extend the life cycle of critical components in the stage. The cooling air (secondary system) can account for 25% of the total bypass air, approximately 5% of the total bypass air is used to seal the disc cavities. To further enhance the benefits of the sealing flow (cooling air), rim seals are fitted at the periphery of both, stationary and rotating discs. Rim seals help to further reduce the ingestion of hot mainstream gases (combustion chamber gases) that can cause damage to the discs and blade roots. The cause of hot gas ingestion is principally due to the circumferential pressure asymmetry in the mainstream flow, furthermore, the mixing between the sealing flow and mainstream gas, results in a deterioration of aerodynamic performance. The first part of this thesis concerns experiments using a 1.5-stage turbine rig, from which the flow physics associated with ingestion could be studied. This thesis presents experimental results using the turbine test rig with wheel-spaces, upstream and downstream of a rotor disc. Ingress and egress were quantified using a CO2 concentration probe. The probe measurements have identified an outer region in the wheel-space and showed a flow structure consistent with Batchelor-type flow. This is the first time asymmetric variations of concentration have been shown to penetrate through the seal clearance and the outer portion of the wheel-space. For a given flow coefficient in the annulus, the concentration profiles were invariant with rotational Reynolds number. The measurements reveal that egress flow provides a film-cooling benefit, on the vane and rotor platforms. The second part of this thesis investigates the effects of ingress through a double radial rim seal. The effect of the vanes and blades on ingress was investigated by a series of carefully controlled experiments: firstly, the position of the vane relative to the rim seal was varied; secondly, the effect of the rotor blades was isolated using a disc with and without blades. Measurements of steady pressure in the annulus show a strong influence of the vane position. The relationship between sealing effectiveness and purge flow rate, exhibited a pronounced inflexion for intermediate levels of purge; an inflexion did not occur for the experiments with a bladeless rotor. Shifting the vane closer to the rim seal, and therefore the blade, caused a local increase in ingress, at the inflexion region; again, this effect was not observed in the bladeless experiments. Unsteady pressure measurements revealed the existence of large-scale flow structures (flow instabilities) which depended weakly on the vane position but strongly on the sealing flow rate. Unsteady pressure was measured with and without the blades on the rotor disc. In all cases, the flow structures rotated close to the disc speed. The third part of this thesis involves, experiments and computations of flow through a gas turbine chute seal. The study investigates ingress and the phenomena of flow instabilities. The aim of this study is to investigate the steady and unsteady flow features, near the rim seal mixing plane, for a geometrically scaled stage with a chute seal. The work presented here forms part of a future partnership with the KTH Royal Institute of Technology, to study the effect of engine scaling on ingress. Experiments and computations for; pressure, swirl and sealing effectiveness, were done at an engine representative turbulent flow (lT) condition. Under this condition, an engine representative wheel-space flow structure exists. CFD results suggest that flow instabilities influence ingress, instabilities caused by a shear interaction between the egress and mainstream. This supports the hypothesis of flow instabilities being driven by shear gradients. The final part of this thesis investigates re-ingestion. A mixture of upstream egress flow and mainstream, gets re-ingested in the downstream wheel-space. Re-ingestion was experimentally measured and evaluated using a model developed by Prof. Mike Owen. To the author’s knowledge, it is the first time this methodology has been applied to quantify re-ingested fluid in downstream wheel-space. The results showed that the upstream egress does not influence the fluid dynamics, downstream of the rotor blades. The experiments were conducted at incompressible flow conditions. Probe concentration measurements demonstrated that, an interaction occurs between the re-ingested fluid and the downstream egress flow, at the rim seal mixing region. Re-ingestion was evaluated for a range of sealing flow rates. It was shown that the mass fraction of re-ingestion increases with increasing downstream seeded sealing flow rate.

The gas turbine engine is undoubtedly one of the most versatile engines, with applications ranging from aircraft, maritime and locomotive propulsion to electricity generation. Increasing fuel costs and strict environmental legislation demand increasingly efficient engines. Engine efficiency can be improved by operating at a turbine entry temperature (TET) beyond the melting point of the turbine components. To enable this, compressor flow is diverted to the turbine for cooling and sealing the cavities (or wheel-spaces) formed between adjacent stator and rotor discs. Insufficient sealing flow reduces component operating life and superfluous use reduces the benefits of increased TET.Rim-seals, fitted at the periphery of the rotor discs, are used to minimise the ingress of hot gas and therefore reduce the amount of sealing flow required. These rim-seals are designed using computational fluid dynamics (CFD) software which require experimental validation in facilities operating at engine-simulated conditions as well as experimental rigs operating at low Reynolds number. This thesis presents: (i) the design, assembly and commissioning of a new 1.5-stage turbine experimental facility, (ii) measurements of ingress through generic seals in an upstream and downstream wheel-space and (iii) parametric studies of the performance of eight Siemens proprietary seals. The new 1.5-stage test facility is designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. The flow structure inside the wheel-spaces is representative of the one found in engines with the rig operating at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing-flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of concentration effectiveness based on carbon dioxide gas concentration, pressure and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. For both single and double radial-clearance seals, the measurements show that the concentration effectiveness in the core is equal to that on the stator and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space, and that the fluid from the boundary-layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The variation of concentration effectiveness with sealing flow rate in the upstream and the downstream wheel-spaces is obtained and found to be independent of rotational Reynolds number for a common flow coefficient in the mainstream annulus. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the orifice model can accurately capture the variation of effectiveness with sealing flow rate in both wheel-spaces. The driving mechanism for ingress in the downstream wheel-space is identified using concentration effectiveness measurements taken in a rotationally-induced (RI) ingress experiment. The measurements of the RI test were found to be equal to those of the externally-induced (EI) ingress test, showing that RI ingress dominates in the downstream wheel-space. Three parametric studies including eight Siemens proprietary seals were performed in the downstream wheel-space using measurements of carbon dioxide concentration, swirl ratio and pressure. In the first study it was proven that the inter-blade gaps in engines have a negative effect on the performance of the seals. In the second study it was shown that a significant decrease in ingress can be achieved by using a compound angel-wing/radial-clearance seal as opposed to a simple angel-wing seal. In the third study the negative effect of the introduction of a buffer cavity in the design of seals for the downstream wheel-space was revealed. In all cases, the majority of the wheel-space was dominated by the expected flow structure and good agreement between the theoretical orifice model and experiments was observed despite the complex geometry of the seals.

The gas turbine engine, as an adaptable source of power, has been used extensively for electric power generation, mechanical drive and jet propulsion. Driven by competition within the industry, gas turbine engine manufactures strive to produce ever more efficient products that also comply with emission regulations. The overall efficiency, as a crucial parameter governing engine performance and life cycle operating costs, depends on a high turbine inlet temperature, as well as an appropriately high pressure ratio across the compressor. The turbine components operating at elevated temperatures could experience serious problems, such as unwanted creep, oxidation or thermal fatigue, which compromise the integrity and reduce lifespan. In modern gas turbine engines, cooling air bled from the compressor is used to prevent overheating of the turbine, through the secondary air system. As much as 25% of the compressor air bypasses combustion to be used for cooling and sealing purposes. Hot gas ingress is one of the most important and intricate problems of the secondary air system faced by engine designers. Ingress occurs when the hot gas from the mainstream is ingested into the wheel space, formed by the turbine disc and its adjacent casing. A rim seal is fitted at the periphery of the wheel-space, and a sealing flow of coolant is used to purge the cavity reducing or preventing ingress. Sufficient sealing flow is required, but an excessive use of coolant decreases overall engine efficiency. Therefore, from engine designers’ perspective the use of sealing air must be minimised. Optimisation of the rim-seal design is a crucial approach to fulfil the purpose. The double-clearance rim seal is widely employed in gas turbines, which consists of an outer-seal at the periphery of the wheel-space and an inner-seal located radially inboard. The annular cavity formed between the double-seal arrangement is known to predominantly confine the ingested hot gases, thus significantly reducing ingestion inboard of the inner seal. In order to study how double-clearance seals operate in depth, this thesis describes a new single stage turbine research facility, designed for conducting extensive and comprehensive experimental studies on ingress for different rim-seal configurations. Experimental study conducted with the new facility is reported for a variety of generic but engine-representative double-clearance seal configurations, to gain insights into the sealing effectiveness and fluid dynamics associated with different rim-seal design features. Besides being adaptable for various rim-seal configurations, the research facility was also designed to be highly versatile in respect of wheel-space geometries and gas path blading, in order to investigate the impact on ingress from the aerodynamics both inboard and outboard of the rim seal. Extensive instrumentation was incorporated into the turbine stage for the measurements of pressure, swirl velocities, gas concentration and temperature. Additionally, the facility is capable of modelling leakage flow paths found in actual gas turbines to explore novel techniques that could reduce ingress by utilising the leakage air. A parametric study is presented for a range of double-clearance rim seal configurations, characterised by various design features both on the stator side and rotor side of the turbine disc system. Gas concentration measurements were made for each configuration to assess the relative sealing performance. The sealing effectiveness was determined both in the outer wheel-space between the double clearances, and in the inner wheel-space radially inboard of the inner-seal. These measurements constitute a research database that will support the design approach at Siemens, in conjunction with the theoretical model previously developed at Bath, which treats the seal clearance as an orifice ring and uses adapted Bernoulli’s equation to correlate sealing flow rate and pressure difference across the seal. The sealing effectiveness is correlated with pressure and swirl ratio in the wheel-space to study the fluid dynamics associated with different rim-seal features, in support of rim-seal design and optimisations for secondary air systems.

The work described in this thesis aims to conduct a systematic study of the two stage turbocharging system to improve the Diesel engine transient performance as well as NOX and CO2 emissions with a focus on the improved turbocharger matching and the control of the charging system, through the use of high fidelity engine models backed by experimental results. To perform the analytical study, commercial 1D simulation software has been used in the process of system characterisation and control strategy design. To validate the analytical results, a two stage turbocharging system was installed on a production diesel engine and tested on a transient engine test bench. The test results were then used to further calibrate the 1D engine/turbocharger model. Several other technologies were also investigated in simulation to explore their potential to further improve the system. Unlike most studies in the literature, this project focused on the system benefit of the engine and turbochargers, instead of conducting optimisation solely at the component level. The engine global parameters, such as the engine fuel consumption, emission levels and the transient response were the main parameters to be considered and were also best suited to the strengths of the 1D simulation method. The interactive use of both the analytical and experimental methods was also a strong point of this study. A novel control strategy for the system was proposed and demonstrated in the simulation. Experiments confirmed the validity of this control strategy and provided data for further model calibration. The comparison of the test results of the baseline engine to those obtained with the two stage turbocharged engine system verified the benefits of the novel turbocharging arrangement and control scheme. Transient response (T1090) was improved, with a 50% faster torque rise at 1000 rpm; the fuel consumption over the NEDC was 4% lower and NOx emissions over the NEDC were 28% lower. In the meantime, the study also revealed shortcomings of the system, such as the lack of EGR control at low speed, low load condition and a mid-speed fuel consumption deterioration of 13% on average at 3000 rpm due to excessive back pressure. With a novel 1D model corroborated using test results, exploratory simulation was done to rectify the aforementioned shortcomings and to further improve the system. Simulation results showed that by implementing VGT and ball bearing technology in the high pressure stage of the two stage system, the EGR controllability at low speed was regained and the excessive back pressure at high speed was improved. Consequently, the fuel consumption was only increased by 1.3% compared to the baseline NEDC operation and the transient response was on par with the original two stage system, with only 0.05s slower in torque rise at 1000 rpm, and still 48% faster than the baseline VGT system. Furthermore, the NOx emission can be expected to be greatly improved in the upcoming more intensive drive cycles compared to the NEDC cycle, with simulation showing NEDC NOX emissions dropped by 1%, comparing to a substantial reduction of 11% in WLTC.

This thesis experimentally investigates the phenomenon of ingress through gas turbine rim seals. The work focuses on developing experimental and numerical techniques for measuring the required sealing flow levels to purge the wheel-space against ingress and the effect of externally-induced ingress on the surface temperature as well as heat transfer to the rotor. Ingress is driven by a pressure difference between the mainstream annulus and wheel-space cavity resulting from the asymmetric external pressure profile in the annulus and/or the rotation of fluid in the rotor-stator wheel-space cavity. It can be prevented by pressurising the wheel-space through the supply of sealant flow. The University of Bath had measured and shown, for the first time, the thermal effects of ingress on the rotor in the wheel-space for a datum seal (axial-clearance seal) using thermo-chromic liquid crystal. However, as the previously used experimental technique with thermo-chromic liquid crystal was prone to large uncertainties, a non-intrusive temperature measurement technique using an infrared (IR) temperature sensor was developed. The new technique was successfully applied to the Bath one-stage gas turbine test facility and provided a full temperature history of the rotor surface in a transient heat transfer experiment. Moreover, a data analysis method appropriate for transient experiments using the IR temperature measurement technique was developed. The method was used to accurately calculate the heat transfer coefficient and the adiabatic surface temperature based on the full temperature history. A series of numerical experiments was carried out to develop the analysis method and the results from the numerical experiments were used to design new heat transfer experiments for both the 1 and 1.5-stage ingestion rigs of the University of Bath. Gas concentration measurements were made on the stator of the Bath one-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for four different seal geometries at design operational conditions. The IR temperature measurement technique was used to determine the effect of ingress on the heat transfer coefficient and the adiabatic wall temperature on the rotor of the ingestion test facility. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs (stator and rotor). Comparison between the adiabatic effectiveness on the rotor and the concentration effectiveness on the stator showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which was drawn into the rotor boundary layer from the source region, thermally buffered the rotor against the ingested fluid in the core. Subsequently, a thermal buffer ratio hypothesis was developed and shown to be in good agreement with the experimental data. A previously published orifice model was modified so that the sealing effectiveness determined from the concentration measurements in a rig could be used to determine the effectiveness based on pressure measurements in an engine. There was good agreement between the effectiveness acquired from pressure measurement determined using the theoretical model and the sealing effectiveness determined from concentration measurements. It was also shown how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine.

Gas turbines are one of the most widely-used power generating technologies in the world today. In the face of climate change and continued global financial pressures placed on industries, one of the biggest challenges facing engine designers is how to continually improve turbine efficiencies. Rim seals are fitted in gas turbines at the periphery of the wheel-space formed between rotor discs and their adjacent casings. These seals reduce the ingestion of hot gases that can cause catastrophic damage to some of the most highly stressed components in the engine. In gas turbine engines this ingestion is principally caused by circumferential pressure asymmetries in the mainstream annulus, radially outward of the rim seal. A superposed sealant flow, bled from the compressor, is used to reduce or, at the limit, prevent ingestion. As the use of this sealing air can reduce the cycle efficiency, it is important to know how much flow is required to prevent ingestion and to understand the associated fluid dynamics and heat transfer when ingestion occurs. This thesis presents experimental results from a specifically designed research facility which models an axial turbine stage with generic, but engine-representative, rim seals. The test section featured stator vanes and symmetrical rotor blades. Measurements of pressure, CO2 gas concentration and swirl ratio are used to assess the performance of different seal designs. Although the ingestion through the rim seal is a consequence of an unsteady, three-dimensional flow field, and the cause-effect relationship between pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a theoretical orifice model. Effectiveness data were collected at the design condition for a datum radial-clearance single seal, and compared with a double overlap equivalent and a further derivative with a series of radial fins. The benefit of using double rim seal configurations was demonstrated, where the ingested fluid was shown to be predominately confined to the outer wheel-space between the two sets of seals. The radial fins increased the level of swirl in this outer wheel-space, rotating the captive fluid with near solid body rotation. This improved the attenuation of the pressure asymmetry which governs the ingress, and improved the performance of the inner geometry of the seal. A criterion for ranking the performance the different seals was proposed, and a performance limit was established for double seals, in which the inner seal is exposed to rotationally induced ingress only. Experiments were also performed at off-design conditions, where the effect on ingress of varying the flow coefficient (CF) was demonstrated for both under-speed and over-speed conditions. The correlated effectiveness curves were used to predict the required levels of sealant flow to prevent ingestion, and the variation with CF was in mainly good agreement with the theoretical curve for combined ingress, which covers the transition from rotationally induced to externally induced ingress. Departure of the measured values from the theoretical curve occurred at very low values of CF for all the seals tested. This was attributed to flow separation at large deviation angles between the flow and the symmetric turbine blades. The effectiveness measurements determined from gas concentration were then used to establish a new effectiveness based on pressure. A hypothetical location on the vane platform was assumed to exist where the measured pressures would ensure consistency between the two definitions. Experimental measurements for a radial clearance seal showed that as predicted, the normalised pressure difference across the seal at this location was linearly related to the pressure difference at an arbitrary location on the vane platform. When compared to the original concentration effectiveness measurements, good agreement was found with the values of effectiveness determined by the theoretical pressure model. It was shown in principle how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine. The design of a novel 1.5-stage facility, complete with representative turned rotor blades, is then described. The rig experimentally models hot gas ingestion in a downstream, as well as an upstream wheel-space. The methodology behind the design process was outlined, and details were given on the proposed design operating conditions. Experience gained from conducting experiments in the previous facility heavily influenced the design of the new rig. The instrumentation capabilities have been summarised and an explanation of the intended measurements given.

Modern diesel engines are being continuously developed in order to improve their specific output thus reducing the fuel consumption. This is in response to both increasingly stringent regulations and to the demands of the customer evolving. With this in mind a more detailed understanding of some of the fundamental processes within the engine are required. A prime example of one of these processes is heat transfer. In the region of 17-35% of fuel energy will pass to the coolant, therefore the rate of heat transfer has a considerable effect on the design and function of the engine. This thesis describes a method to calculate heat transfer through a combustion chamber wall of a modern production engine and uses the data to improve the understanding of the impact of active thermal management systems on the rate of heat transfer and how this can be incorporated into empirical modelling, also improving fundamental understanding and evaluating established correlations focusing on the warm-up period. Development of prototype engines over extended test schedules can prove expensive, therefore in order to reduce the necessary test and development period of a new engine it is useful to be able to predict the heat transfer within the combustion chamber using modelling data. A large number of correlations have been developed over the years, however with the rate of development of the diesel engine; some of these correlations have been left behind. A number of steady state operating conditions were employed to approximate the New European Drive Cycle. By approximating the drive cycle performance it was possible to further the understanding of the effect of changing the engine operating conditions on the temperature distribution in key areas of the engine, including the crankshaft bearings, camshaft bearings and combustion chamber walls. The main focus of this thesis is the cylinder wall temperatures and the rate of heat transfer through the cylinder wall from the combustion gases. It was found that there was a temperature rise of 7°C between the oil in the main oil gallery and that used to lubricate the journal bearings; however the oil in the camshaft bearings was found to decrease in temperature along the inlet camshaft but increase along the exhaust camshaft. In addition the temperature and heat transfer profiles were significantly different between the inlet and exhaust sides of the engine. Existing correlations were found to in general over-predict the gas side convective heat transfer coefficients at high power conditions. The accuracy of these correlations could be improved by 77.6% by modifying the correlation coefficients; however the introduction of a cylinder wall temperature component, in addition to modifying the correlation coefficients, led to an improvement in the correlation by a further 17.4%. Prototype hardware and a Design of Experiments (DoE) based test programme were used to investigate the impact of actively changing the external oil and coolant circuits during a New European Drive Cycle on the engine warm-up. It was found that the driving force for improved warm-up when throttling the engine coolant flow was the increase in the gas side wall temperature, and the reduction in the local coolant temperature. The coolant local to the combustion chamber wall was cooler as it remained isolated from the majority of the external cooling system. In addition, the low engine coolant flow retained the heat energy which had been transferred through the cylinder wall, within the engine structure. This unique approach of combining cylinder wall temperature measurements and active thermal management systems allowed for the fundamental heat transfer paths to be explained. The insight obtained during the steady state experiments and the transient tests was then used to evaluate the potential to calculate the convective heat transfer during different stages of the engine warm-up. A strong correlation, a R-squared of between 0.77 and 0.83, was found between the rate of energy transfer to coolant across the engine and the gas side convective heat transfer coefficient during early stages of the drive cycle, however this decayed as the engine warmed up. A correlation was also found between the convective heat transfer coefficient and the temperature used by the ECU for engine control, in this case measured in the cylinder head. The modified convective heat transfer correlation developed in this thesis allows for the gas side convective heat transfer coefficient to be estimated at different stages of the engine warm-up based on the average cylinder wall temperature. This was not possible with existing correlations and could significantly improve thermal modelling during engine warm-up. The findings of this thesis are relevant to engine designers, combustion simulation engineers and thermal management teams as 1-D modelling will continue to play a significant role in the development process of internal combustion engines for the foreseeable future. This is primarily due to the cost implications of high performance computers for 3-D modelling; therefore the development of these models remains vital.

This thesis focuses on the ingress problem in rotor-stator system in turbines with the primary emphasis on numerical methods. The first part of this dissertation implemented a newly-developed orifice model for externally-induced (EI) ingress into a non-commercial one-dimensional (1D) flow network solver. The massflow functions of the EI ingress model are solved with an iterative procedure with inner and outer loop iterations. The comparison of this model against a standard procedure where the fluid exchange is modelled with multiple branches was in good agreement despite a diverging behaviour at high sealing effectiveness. An extrapolation method was developed to extrapolate the sealing parameter Φmin from one Mach number regime to another. This procedure, which uses the linear saw-tooth model for EI ingress, showed good agreement with the computed values of Φmin over the investigated subsonic range. It was proposed to use this method to scale the experimentally determined Φmin value obtained at incompressible test rig conditions to a geometric similar engine at compressible conditions. The effect of aerodynamic off-design conditions (varying flow coefficient, CF ) and their impact on ingress in rotor-stator systems was investigated with transient CFD computations. Pressure measurements behind the trailing edge of the vane showed a linear variation of the non-dimensional pressure coefficient with flow coefficient. This behaviour was confirmed numerically with the exception of a diverging behaviour with an increase of Cp at low values of CF . This effect could be isolated and associated with the rotor blade at large deviation angles. Various rim-seal concepts were numerically investigated with the intent to minimise the ingress levels in the wheel-space of a high pressure turbine. These concepts were experimentally tested at the ingress facility of the University of Bath and confirmed predicting the ranking order of these seals by the numerical investigation. An optimised rim-seal design was developed from this study which addresses the root cause of the EI ingress by attenuating the tangential pressure variation; the new rim-seal reduced the sealing parameter Φmin by about 40% compared a the baseline case. A numerical study investigated several rotor endwall concepts with the objective to minimise the mixing loss associated with the interaction of the egress with the mainstream flow. A 3D concept with leading edge feature along with an incorporated egress channel within the endwall reduces not only the interaction loss but also losses associated to secondary flows, (i.e. horse show vortex and cross passage flow), without negatively impacting the ingress levels of the upstream located wheel-space.

Increasing environmental constraints have led to a corresponding increase in engine complexity. As a result there is more of a requirement to fully understand and manage the task of hardware selection and engine optimization. Traditionally undertaking these tasks in either experimental or simulation environments would be highly time and cost inefficient and iterative. A technique is developed whereby data is merged from a variety of sources thus reducing the aforementioned problems whilst still retaining high system knowledge. Technologies relating to engine downsizing are focused on since it has been identified as one of the more promising methods in meeting future CO2 constraints. Engine downsizing is a smaller highly boosted engine performing the same role of a larger engine with reduced heat and frictional losses. In order to address these issues this research develops a range of techniques that enable technologies such as high boost, variable valve actuation (WA) , variable compression ratio (VCR) and exhaust gas recirculation (EGR) to be evaluated as part of the overall powertrain optimization process. A novel experimental data merging process proved to be the most successful method and showed improved accuracy over simulation studies, particularly with reference to NOx and BSFC. As part of the experimental work in capturing high boost data a novel charge air handling unit is employed. This emulates the effects of boosting hardware as opposed to having to develop prototype hardware itself. The advantage is it can operate outside the production envelope and is thus capable of emulating a variety of current and future boosting strategies. Within this research the charge air handling unit reaches 2 bar boost irrespective of engine speed, although there is capacity to go up to 3 bar with a reduced compression ratio engine and uprated gaskets. Further development of the technique at full load will give the automotive engineer an invaluable tool to make informed powertrain selection choices early in the development cycle, thus reducing cost and potential problems at later stages.

Research, pilot scale and field developments of In-Situ Combustion (ISC) for enhanced oil recovery (EOR) in shallow, low pressure, heavy oil reservoirs intensified between the first and the second oil crisis from 1973 to 1981. A decline of interest in EOR followed the collapse of the oil prices in 1986. Renewed interest on in-situ combustion EOR research in the late 1980’s and beginning of the 1990’s was expanded and focused on high pressure medium and light oil reservoirs. The applicability of air injection in deep high pressure light petroleum reservoirs was established by research work of Greaves et al. in 1987 & 1988, Yannimaras et al. in 1991 and Ramey et a l in 1992. Accelerating rate calorimeter (ARC) tests were used to screen the applicability of various types of light oil reservoirs for in-situ combustion EOR by Yannimaras and Tiffin in 1994. The most successful light oil air injection project in the 1990s in the Medicine Pole Hills Unit, Williston Basin, N. Dakota started in 1987 and was reported by Kumar, Fassihi & Yannimaras, in 1994. Low temperature oxidation of light North Sea petroleum was studied at the University of Bath. A high-pressure combustion tube laboratory system was built at Bath University to evaluate performance of medium and light petroleum in-situ combustion processes. Gravity effects and the impact of horizontal wells in Forced Flow In-Situ Combustion Drainage Assisted by Gravity (FFISCDAG) were studied with three-dimensional combustion experiments. In this study, the university of Bath combustion tube experiments have been simulated and history matched. The tube experiments were up-scaled and field simulation studies were performed. A generic PVT characterization scheme based on 5 hydrocarbon pseudo-components was used, which was validated for light Australian and medium ‘Clair’ oil. A generic chemical reaction characterization scheme was used, which was validated for light Australian and medium ‘Clair’ oil. Advanced PVT and chemical reaction characterizations have been recommended for future work with more powerful hardware platforms. Extensive front track and flame extinction studies were performed to evaluate the performance of currently available non-iso-thermal simulators and to appraise their necessity in air injection processes. Comparative ISC field scale numerical simulation studies of Clair medium oil and light Australian petroleum were based on up-scaled combustion tube experimental results. These studies showed higher than expected hydrocarbon recovery in alternative EOR processes for both pre and post water flood implementation of ISC. Further in this study field scale numerical simulation studies revealed high incremental hydrocarbon recovery was possible by gravity assisted forced flow. The applicability of light oil ISC to gas condensate and sour petroleum reservoirs has been examined in this study with promising results. Light petroleum ISC implemented by a modified water flood including oxidants such as H2O2 and NH4NO3 are expected to widen the applicability of ISC processes in medium and light petroleum reservoirs, especially water flooded North Sea reservoirs.

This thesis describes experimental and theoretical work carried out during an investigation into heat release and heat transfer in Diesel engines. Experimental work included steady state measurements of the engine heat balance and local metal temperatures of cylinder liner, cylinder head and pistons. Transient measurements were made of cylinder pressure, fuel line pressure and needle lift. These diagrams were analysed to obtain experimental heat release and fuel injection rate. Theoretical calculations include some equations relating flow through poppet valves to swril generation in the open period, and more detailed treatment of the closed period processes. Two models for the closed period are developed, a relatively simple single zone model in which homogeneous conditions in' the cylinder are assumed, and a two zone model in which conditions are calculated separately for unburnt fuel and air, and combustion products. Relatively high gas temperatures are calculated in the combustion product zone, so gas composition is obtained as a mixture of 12 species using equilibrium calculations. The rate of mixing between fuel and air which controls the rate of combustion is calculated using empirical equations relating the mixing rate to the air swirl velocity and the concentration of combustion products in the mixing region. The theoretical model is at present in an early stage of development. Likely approaches for further theoretical development and experimental confirmation are discussed.

This work is concerned with the prediction of the transient performance of two engine systems associated with high speed Diesel engines. These are an automotive turbocharged Diesel engine and a differential compound engine. The extension of a one dimensional analysis, to cover the transient mode of operation by allowing for component inertias, is described in detail. As a check on the validity of the simulation, a test rig for a turbocharged engine has been built and suitably instrumented. Details of this and the hydrostatic braking system are included. Two different simulations for the turbocharged engine are proposed to predict the transient characteristics of the engine. The first method treats the response between initial and final running conditions as a number of steady state operating points, while the second discriminates between the firing in each cylinder. On the whole accurate predictions were obtained although s me errors occurred mainly in conditions of excess fuelling. The simulations show that under transient conditions the compressor can often work at 'off- design' operating points and may sometimes surge or choke. Some suggestions are made for improving the overall performance of the system. The extension of the work to include the differential compound engine has proved the adaptability of the approach. Further, it has shown the ability of the compound engine to respond rapidly to a demand for a speed change, as the load does not have to be accelerated at the same speed as the engine. During an acceleration the compound engine displays an ability to recover quickly from low values of air to fuel ratio.

The aim of the present study was to produce a theoretical method for estimating air swirl speeds in 4-stroke diesel engines fitted with poppet valves and purely directional inlet ports. This was achieved by building a steady flow test rig and observing the effects of such parameters as inlet port geometry, valve lift, and pressure ratio on the polar velocity outlet profile around the valve head and the swirl speed in the cylinder. From these observations, two theories were developed which enabled the swirl speed in the steady flow rig to be estimated with some degree of accuracy; particularly in inlet ports with inclination angle between 45° and 60°. The two theories were then adapted for inclusion into an existing step-by-step engine synthesis program to find out how swirl speeds vary throughout the engine cycle, and what effect engine speed and boost ratio have on the swirl speeds attained. The synthesised results are not backed up by any experimental data, but the curve shapes obtained were similar to those observed by other workers. Engine speed and boost ratio did not have a great effect on swirl ratio (swirl speed/engine speed).

The results contained within this thesis were taken from a largely experimental project tto compare a conventional turbocharger and the unique Comprex pressure wave supercharger. A large truck Diesel engine, the Leyland 690 was fitted in turn with a Holset H2B turbocharger and a Brown Boveri CX140 supercharger. A series of both steady state and transient investigations was completed with both systems. The turbocharged experimental results were also compared with predicted results from the steady state computer program (EMAT). The introduction gives; a detailed description of the Comprex operation, history, range and applications. The second chapter is devoted to a description of the apparatus and calibration of the instrumentation. The following four chapters give the experimental results in tabular and graphical form, for both systems and for the steady state and transient tests. In Chapter 7 the steady state tests for both systems are compared and the transient tests are compared in Chapter 8. The Comprex supercharger theory is briefly described in Chapter 9 with several ideas of the obtaining the air flow which bypassed the engine under certain conditions. The predicted results for the turbocharged engine are compared with experimental results in Chapter 10. Some of the problems encountered during the experimental testing are discussed in Chapter 11. With the engine operating under steady state conditions, the limiting torque curves for each system were slightly different. At the lower engine speeds (1400 - 8800 revs/min) the engine fitted with the Comprex produced a higher power than with the turbocharger. The specific fuel consumption at higher speeds was marginally better (lower) with the turbocharger but at lower speeds the Comprex produced favourable values. As expected, the boost pressure was higher with the Comprex wnth better air/fuel ratios particularly at the lower engine speeds. Using the Hart ridge smoke meter, the smoke levels with the Comprex were considerably better at the important lower engine speeds. Under transient conditions the Comprex produced considerably better results, especially in the response time to reach steady conditions. This was due to the higher boost pressure ratios at comparable operating conditions. During the very severe changes in load applied to the engine, the Comprex enabled stabilisation within 0.6 seconds compared with 1.5 seconds with the turbocharger. Transient smoke levels, measured by a high response opacimeter were also lower with the Comprex. Despite these very favourable results with the Comprex supercharger, its higher cost and weight, and the added complications associated with the drive and pipework, have so far militated against the wider adoption. However, for certain applications, such as tractors, excavators and shovel loaders with their rapidly changing load and speed cycles, the Comprex has considerable advantages.

The future European trends for truck diesels include improvements to acceleration performance, economy and higher torque over a wider speed range (where maximum speeds are being reduced). A variable geometry turbocharger together with electronic control can combine the conflicting requirements of flexibility and economy in one engine. This thesis investigates the complete testing of a HOLSET turbocharger equipped with a variable area turbine (based on volute exit area and ring sleeve design) applied to an automotive type TL11 engine rated at 190 kW 2100 rev/min. Control was effected by a programmable digital controller and was extended to include variable injection timing and electronic governing functions. An optimal type control strategy was implemented. A description is included of the test facility and the features adopted such that the electronic control system could be developed effectively. An account on the control implementation is given together with details on the design and development of the control parameters. Different control algorithms both steady state and transiently were assessed and resulted in a torque back-up of 46% at 59% of rated speed compared with 21% at 62% of rated speed for the base. Significant improvements to part load efficiency were achieved e.g. .225 kg/kWh island increased by 25%. Boost scheduling controlled ring sleeve position and resulted in enhanced engine acceleration. The limitation to this work included mechanical, breathing and efficiency parameters. These were investigated theoretically. The practical and theoretical work indicated that with appropriate developments an SFC characteristic with better than .200 kg/kWh is readily attainable. Appropriate conclusions were drawn together with suggestions for further work.

The experimental and theoretical investigation of the effect of swirl on the fuel-air mixing process in direct-injection diesel engines is described. The experimental work involved the further development of an existing hydraulic analogue technique which enables excellent flow visualisation. This was followed by the design and construction of a novel high-swirl combustion bomb which reproduces engine conditions under fine control. This experimental apparatus includes facilities for high-speed cine photography and a micro-computer based data acquisition and control system providing flexible software control of the fuel injection equipment and data sampling rates of up to 70 kHz. Typical non-combusting and combusting results are presented. Theoretical models of fuel-air mixing are reviewed. The phenomenological jet-mixing model developed and presented is based on an existing continuum mechanics approach and is solved by an integral method. The model includes momentum, heat and mass transfer and simulates jet cross-section distortion and the non-similarity of property profiles. It is intended that this model will form the basis of a proposed multi-zone combustion model.

This thesis describes a theoretical and experimental programme designed to produce a self optimizing control system to the Differential Compound Engine (DCE). Optimum control surfaces for the relevant variables are obtained experimentally and theoretically and used as the basis for microprocessor control. The system adopted relies on analogue inputs from appropriate transducers to the microprocessor via analogue-to-digital converters with outputs representing optimum control settings implemented via electrohydraulic actuators. An additional theoretical investigation is concerned with further measures to improve efficiency and output torque of the current DCE system particularly through the incorporation of a continuously variable turbine transmission (CVT) and a main drive line torque converter to improve the system. A final theoretical section of the work deals with attempts to determine the best nozzle angle schedule for transient operation, and the application of such a schedule to the calculation of a complete vehicle transient.

As part of a broader research project of adiabatic engine investigation, the present work concerns the effect of heat barriers in the suppression of heat loss and on the thermal loading conditions in pistons, from both a steady-state and transient point of view. The theoretical work has been concerned primarily with the development of a comprehensive set of computer programs dealing with either the steady-state axisymmetric heat transfer and stress analysis, or the transient heat transfer analysis. In developing the programs, the present work provides a subdomain integral approach to the finite element method, the integration of which can be either weighted or non-weighted. In the latter case, the subdomain integral can often be physically interpreted as, e.g. the energy balance in a control volume or the force equilibrium on a free body, hence it provides much more intuitive and physical insights to the finite element method, with the same accuracy and same applicability to solving various engineering differential equations as the Galerkin method. The subdomain integral approach can be directly applied to the initial value problems, where the subdomain is offset in the time-dimension. By this method the time-marching process can be represented in the form of a system matrix, which enables the direct solution of periodic phenomena without the requirement of incorporating and iterating the guessed initial conditions from cycle to cycle. In this way, the convergence from cycle to cyle is inherently satisfied. More importantly, the present work also provides a one-dimensional linearization model of the axisymmetric heat transfer and thermal stress field, from which may be deduced the equivalent thermal resistance (two-terminal model) or its three components (three-terminal model) of the configuration, as well as the thermal stress sensitivity to the thermal loadings. By incorporating the equivalent thermal resistances into the engine cycle simulation program, the heat flow rate over the full cycle in the engine cycle simulation can be matched with the heat flow rate through the combustion chamber components. The experimental work has concentrated on methods for determining the gas-side boundary conditions from measured piston temperatures. The area-mean wall temperatures (and hence the total heat flow through the piston when the effective gas temperature is known), can be obtained from the measured maximum surface temperatures by applying the present one-dimensional model. Furthermore, a novel differential probe is proposed to measure the heat transfer coefficient and the effective gas temperature simultaneously. By applying these specially developed finite-element programs, matched either with the experimentally determined boundary conditions or with the corresponding engine cycle simulation program, a detailed investigation on various heat barrier configurations, concentrating on a specially designed and manufactured air-gap piston, leads to the following conclusions: 1. The practical range of insulation design lies between 40-65% reduction of heat loss. The air-gap piston design presented in this thesis can give about 50% reduction of heat loss, which is in the desired range of insulation. 2. The effect of insulation on the percentage suppression of heat loss is influenced by the engine rating conditions, and by the gas-side boundary conditions. The higher the rating, or the higher the gas-side heat transfer coefficient, the more significant is the effect of insulation on the suppression of heat loss. 3. In the "ideal transient adiabatic" operation, about 50% of the total recovered heat can be converted into work. However, in real thermal barrier configurations, the wall surface temperature fluctuation is small. Therefore, nearly all real thermal barriers (including the air-gap design) undergo "steady-state" operation, where only about 30% of the total recovered heat can be converted into work. 4. Insulation of the piston is not only tolerable, but actually favourable to piston ring life as the ring groove temperature is well below the permissible range. The maximum radial thermal expansion in a high temperature air-gap piston is well below the cold tolerance limit between the piston and the liner. 5. The fatigue analysis shows that the present air-gap design satisfies the demands of fatigue strength. The cyclic thermal stresses in the air-gap piston do not add significantly to the compressive stresses on the crown. 6. By matching the finite element analysis with the engine cycle simulation program, the reciprocal effect of insulation on the gas-side boundary condition in raising the mean effective gas-temperature is clearly shown. The present matching method can thus be used in the further investigation of the effect of insulation on the performance of the whole compound engine system.

This project was a continuation of previous work into the performance predictions of high output diesel engines by mathematical simulation. The project specified that particular attention should be given to the problem of predicting heat transfer. To meet the aims of the project computer programs were developed in FORTRAN for the evaluation of performance. These programs have been used successfully by many people and operate satisfactorily. The computed results were compared with treasured values where possible. Having developed the programs successfully these were used for performance predictions over a very large range of engine parameters for four types of engine, viz four stroke and two stroke valve-in-head, opposed piston and loop scavenge engines. The general trend of the results was that the two stroke engines develop more power than the comparable four stroke engine throughout the range of boost ratio (2 < rc < 6). However, the thennal loading of the two strokes was very much higher and this could well reduce their advantage. A method of calculating heat transfer was developed using a technique called representative velocities. This entailed calculating a representative value of the gas motion in the cylinder and relating this to the heat transfer. The method gave reasonable results for two stroke uniflow scavenge engines, using unadjusted common beat transfer expressions. It was found necessary to derive a purely empirical relationship for four stroke and two stroke loop scavenge engines. The mathematical models and the programs arc discussed in this volume.