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.

This research has examined the combustion and emissions of a spray-guided direct-injection spark-ignition (DISI) engine using exhaust gas recirculation (EGR). The impact of EGR type, swirl and tumble intake airflows, compression ratio and fuel type were also investigated. EGR addition resulted in significant fuel consumption improvements and differing particulate matter (PM) behaviour depending on the knock limited maximum brake torque (KLMBT) spark advance achieved. When comparing EGR types, cooled EGR achieved the best fuel consumption and cooled EGR after three-way catalyst (TWC) achieved the best gaseous emissions (NOx and HC). Swirl and tumble intake airflows significantly increased fuel consumption. However, these increases could be minimized with EGR addition. Swirl significantly reduced the accumulation mode particulate emissions, providing a potential solution for PM reduction. EGR addition did not significantly affect PM for the swirl and tumble intake airflow conditions. 20%vol 1-butanol addition to gasoline fuel (Bu20) resulted in significant PM reductions at 8.5 bar IMEP. At 7.0 bar IMEP, EGR addition allowed the KLMBT spark timing to be advanced, as the compression ratio was increased. Fuel consumption was improved by 0.4% due to the spark advance and reduced pumping losses, and PM improved because the formation of primary particles was reduced.

Premixed compression-ignition (PCI) combustion techniques using low-cetane fuels, including Dieseline (mixture of diesel-gasoline) and naphtha, were investigated in a light-duty multi-cylinder CI-engine focusing mainly on reducing emissions while maintaining or improving the brake-thermal-efficiency. Different fuel-injection and intake/exhaust handling strategies were investigated in a wide engine operating load range from 1.4 to 17.3 bar BMEP. Moreover, an out-cylinder emission reduction technique through using a diesel-oxidation-catalyst (DOC) was investigated. Hot (uncooled) exhaust-gas-recirculation (EGR) combined with low fuel-injection-pressure (as low as 150 bar) significantly enhanced combustion-performance (COV < 5%) and reduced carbon-monoxide and hydrocarbon emissions at lower loads, when using low-cetane fuelled PCI techniques. At 1.4 to 6 bar BMEP, particulate emissions were reduced by >99% with respect to the diesel-CI baseline, in terms of number and mass, while maintaining brake-specific-NOx below 0.4 g/kWh. At loads more than 6 bar BMEP, double-injection strategy advanced combustion-phasing, where the first injection-event was shown to be significantly influential. Due to narrower boiling-range of naphtha compared to Dieseline, naphtha PCI resulted in high-COV at low loads, while it resulted in rapid-combustion at medium/high loads. Utilisation of the hot-EGR is a “win-win” strategy to enhance the combustion-process of the PCI-engine and reduction of the volatile/semi-volatile compounds using the DOC.

Time-delay feed-forward Artificial Neural Networks are examined for gasoline engine cylinder pressure reconstruction using both measured crank kinematics obtained from a shaft encoder, and measured engine cylinder block vibrations obtained from a production knock sensor. Initially, the study focuses on the information content associated with measured data, which is considered to be of equal importance to the particular network architecture and the training methodology. Several hypotheses are constructed, which when tested, reveal the influence of the data information content on the reconstruction potential and limitations. These hypotheses are tested on real data from a 3-cylinder (DISI) engine. Three distinct ideas emerge through this testing process, which are combined to produce a single pressure reconstruction methodology. Reconstruction results obtained via this methodology, applied to crank kinematics associated with steady-state engine operation, show a marked improvement over previously published reconstruction accuracy. Moreover, in steady-state engine operation, the application of this methodology to acceleration measurements of cylinder block vibration, obtained from a knock sensor, show very significant improvements over previous attempts. But the direct application of this same reconstruction methodology to transient engine operation, proves to be problematic. However, a novel generalisation of the approach in the form of a time-dependent feed-forward neural network is proposed and the required adaptation made to the use of the Levenberg-Marquardt training algorithm. This time-dependent approach has been tested under limited transient conditions and shown in the thesis to give good results, therefore offering considerable potential for use with real engine operation. Overall, the thesis shows that by careful processing of measured engine data, standard neural network architectures and standard training algorithms can be used to reconstruct engine cylinder pressure.

The present research describes an investigation of the flow through the inlet port and the cylinder of an internal combustion engine. The principal aim of the work is to interpret the effects of the port shape and valve lift on the engine's "breathing" characteristics, and to develop a better understanding of flow and turbulence behaviour through the use of Computational Fluid Dynamics (CFD), using a commercial available package STAR-CD. A complex computational mesh model was constructed, which presents the actual inlet port/cylinder assembly, including a curved port, a cylinder, moving valve and piston. Predictions have been carried out for both steady and transient flows. For steady flow, the influence of valve lift and port shape on discharge coefficient and the in-cylinder flow pattern has been examined. Surface static pressures predicted using the CFD code, providing a useful indicator of flow separation within the port/cylinder assembly, are presented and compared with experimental data. Details of velocity fields obtained by laser Doppler anemometry in a companion study at King's College London, using a steady flow bench test with a liquid working fluid for refractive index matching, compared favourably with the predicted data. For transient flow, the flow pattern changes and the turbulence field evolutions due to valve and piston movement are presented, and indicate the possible source of cyclic variability in an internal combustion engine.

No description available.

The losses in an internal combustion engine are dominated by thermal and parasitic sources. The latter arises from mechanical inefficiencies inherent within the system, particularly friction in load bearing conjunctions such as the piston assembly. During idle and at low engine speeds, frictional losses are the major contributor to the overall engine losses as opposed to the dominant contribution of thermal losses under other driving conditions. Given the relatively small size and simple structure of the top compression ring, it has a disproportionate contribution to the total frictional losses. This suggests further analysis would be required to understand the underlying causes of compression ring behaviour throughout the engine cycle. The available literature on tribological analyses of compression rings does not account for the transient ring elastodynamics. They usually assume a rigid ring for film thickness and power loss predictions, which is not representative of the ring's dynamic response. A combined study of ring elastodynamic behaviour and its tribological conjunction is a comprehensive approach.

No description available.

L'impact de la dynamique des gaz sur la chaine d’air s'est imposé fortement en raison du contenu de la dynamique dans les nouveaux cycles de test automobile tels que le WLTC. Cela rend les modèles 0D actuels moins fiables car ils reposent sur plusieurs positions sur les cartographies mesurées sur des points de fonctionnements stationnaires. En outre, les phénomènes d'onde et les effets inertiels des gaz sont intrinsèquement négligés. Une méthodologie pour reproduire efficacement les effets d'ondes le long des conduites de moteurs à combustion interne a été présentée dans ce travail. L'idée est basée sur la combinaison des modèles à paramètres concentrés et les modèles quasi-unidimensionnels. Cette combinaison donne la possibilité de prendre les effets d'inertie de la dynamique des gaz tout en évitant le coût lourd de calcul de l'approche de modélisation 1D. La première partie s'est intéressée aux schémas numériques à une dimension, dans le but de les évaluer par rapport aux temps de calcul, d’exactitude et de définir une bonne référence pour davantage validations numériques pour les modèles réduits. Le modèle « quasi-Propagatory » était le meilleur candidat pour modéliser les ondes avec moins de puissance de calcul. Pour avoir une propre estimation de la pression de suralimentation, on s'est intéressé plus particulièrement au compresseur. Un modèle physique a été présenté on se basant sur les travaux de Martin et al. [55]. Finalement, les développements sont validés expérimentalement sur tous les points de fonctionnement du moteur. / Gas dynamics impact on air system dynamics and hence on combustion products, i.e. emissions, has imposed itself strongly due to the dynamics content in new test drive cycles such as the WLTC. This makes current real-time 0D models less reliable as they rely on stationary measured look up tables. In addition, wave phenomena and gas inertial effects are inherently neglected. This makes the estimation of the flow into and from the cylinder inaccurate. A methodology to efficiently reproduce wave effects along the internal combustion engine ducts was presented in this work. The idea relies on combining both lumped parameter and quasi-one-dimensional models. This combination gives the possibility to take inertial effects of gas dynamics while avoiding the heavy computational cost of the 1D modeling approach. The first part investigated one-dimensional numerical schemes, with the aim of evaluating them with respect to real-time applications and defining a good reference for further numerical validations for the low order models. The Quasi-Propagatory model was the best candidate to model waves with less computational power. To have a proper boost pressure estimation, more focus was on the compressor. A physics based model was presented based on [55]. Results have also shown a better interpretation and extrapolation ability. Finally, the developments have been validated experimentally using the complete engine operation map.

The GDI engine has a number of practical advantages over the more traditional port-fuel injection strategy, however a number of challenges remain the subject of continued research in an attempt to fully exploit the advantages of the GDI engine. These include complex in-cylinder flow fields and fuel-air mixing strategies, and significant temporal variation, both through an engine cycle and on a cycle-by-cycle basis. Despite advances in experimental techniques, the relative difficulty and cost of taking detailed measurements remains high, thus computational techniques are an integral part of research activities. The research work presented in this thesis has focused on the use of detailed 3D-CFD techniques for investigating physical phenomena of the in-cylinder flow field and fuel injection process in a single cylinder GDI engine with early injection event. A detailed validation of the numerical predictions of the in-cylinder flow field using both the RANS RNG k-ε turbulence model and the Smagorinsky LES SGS turbulence model was completed with both models showing good agreement against available experimental results. A detailed validation of the numerical predictions of the fuel injection process using a Lagrangian DDM and both RANS RNG k-ε turbulence model and Smagorinsky LES SGS turbulence model was completed with both models showing excellent agreement against experimental data. The model was then used to investigate the in-cylinder flow field and fuel injection process including research into: the three dimensional nature of the flow field; intake valve jet flapping, characterisation, causality and CCV, and whether it could account for CCV of the mixture field at spark timing; the anisotropic characteristics of the flow field using both the fluctuating velocity and turbulence intensity, including the increase in anisotropy due to the fuel injection event; the use of POD for quantitatively analysing the in-cylinder flow field; investigations into the intake valve, cylinder liner and piston crown spray plume impingement processes, including the use of a multi-component fuel surrogate and CCV of the formed liquid film; characterisation and CCV of the mixture field though the intake and compression strokes up to spark timing. Finally, the predicted turbulence characteristics were used to evaluate the resultant premixed turbulent combustion event using combustion regime diagrams.