Recent developments in automotive engines have been directed towards the reduction of engine emissions in order to minimise their effect on the environment. A major part of this advancement has been the improvement of new direct injection injectors providing improved atomisation and better control of the fuel delivery into the combustion chamber. To aid the injector design process, it is vital to understand the fundamental fluid dynamic processes controlling atomisation of high-pressure fluids in Direct Injection injectors. The research effort is directed towards the ability to link changes to the internal nozzle geometry and flow field to the external atomisation processes. This thesis presents a detailed laser diagnostic investigation of Diesel and gasoline direct injectors for automotive applications.

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 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).

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.

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.

This work examined the performance of swirl burners using different injection strategies for various substitute fuels. The research procedure involved various stages; firstly, an assessment study between two liquid fuels, a pure biodiesel and saturated biodiesel, compared to kerosene. Atomization forms were obtained, and a combustion test campaign was initiated using a generic swirl burner. Emissions and power outputs were measured at gas turbine relevant equivalence ratios. Excess oxygen and atomization trends in the biodiesel seem to be playing a significant role in the creation of emissions and flame stability when compared to kerosene. Secondly, an experimental study on the combustion of methane-carbon dioxide mixtures was achieved. Gas mixtures were examined by using different injection strategies with and without swirl and with and without central injection. A smaller 20-kW swirl burner was used to analyse stability and emissions performance by using these blends and to study the impact of CO2 addition. The burner configuration comprised a centre body with an annular, premixed gas/air jet introduced through five, 60° swirl vanes. CO2 dilution reduced flame stability and operability range. The introduction of CO2 decreases temperatures in the combustion zone thus producing a lessening in emissions of nitrous oxides across all equivalence ratios. Regarding injection regimes, the external purely premixed injection system has lower NOx and CO. Addition of CO2 increases the lean blowout limit of all blends. In the last section, a new burner was finally employed to carry out trials using multi-phase injection, where, experimental work investigated the performance of a swirl burner using various mixtures of CO2/CH4 blends with either diesel or biodiesel derived from cooking oil. The swirl burner was employed to analyse gas turbine combustion features under atmospheric conditions to quantify flame stability and emissions by using these fuels. The results revealed that the use of biodiesel and CO2/CH4 blends mixtures led to lower CO production. Results showed that a notable reduction of ~50% in NOx was obtained at all conditions for the biodiesel blends.

The problem consists of selecting simple and combined gas-turbine cycles with high thermal e±ciency and low capital cost is the subject of this study. In order to solve this problem, the so-called thermoeconomic optimization approach was used by se- lecting an appropriate objective function that combines the expenditures of ¯nancial resources (economic) and thermodynamic equations. Recently, a new de¯nition of objective function has been proposed to take into account environmental considera- tions as well. Thermoeconomic optimization is still an open research problem and currently under investigation. The present study is a part of ongoing research aimed at development of Techno-economical Environmental Risk Analysis (TERA) method- ology at Cran¯eld University for the evaluation of advanced power plant concepts in order to meet challenging environmental goals. The object of this work is to apply \design" and \operation" types of thermoeconomic optimization method to a simple and a combined gas-turbine cycle with pollution reduction. The optimization pro- cess adapts updated models for power demand patterns, legislation, capital cost, and in°ation. The outcome of study is the design of cost e±cient systems with reduced environmental impact. Cont/d.

During operation, gas turbine components undergo various types of timedependent degradation due to high temperatures and mechanical loading. In the case of stationary GT engines for mechanical power, creep failure mechanism problems are a very common cause of mechanical failure that significantly reduces component life. The magnitude of the adverse effect is highly dependent on the operating conditions and design parameter of the components. Against this background, the research programme was aimed at achieving a better scientific understanding of the major reasons for creep failure. This would allow mechanical equipment to keep running free creep problem for longer. Therefore, the aim of this research was to develop an analytical life model capable of assessing the influence of humidity on the turbine blade heat transfer and cooling processes considering the engine design parameters, operating conditions and working environment which, in turn, affect blade creep life. The whole cooled blade row is regarded as heat exchanger with convective/film cooling and a thermal barrier coating. The approach is based on an engine performance model, heat transfer models and the change of properties of moist air as a function of water to air ratio (WAR). The changes of fluid properties due to the presence of water vapour were not only considered through a variation of the specific heat, the ratio of major specific heats and gas constant, but also with the variation of density, Reynolds number, Nusselt number and other related parameters. Cont/d.