The work presented here quantifies the forces applied to the main bearings of three six-cylinder turbocharged diesel engines and reviews their exciting properties in both time and frequency domains. The engine structure response at the bearing supports and the outer surfaces are correlated. Vibration acceleration was measured, in the three different directions, at the engine main bearings and the outer surface. The liner vibrations were also measured. A theoretical model for calculating the bearing forces and estimating the bearing moment characteristics is proposed. The calculated bearing forces are investigated in both time and frequency domains. The characteristics of the forces driving the piston across the cylinder clearance are calculated. The characteristics of the forces acting on the liner by the piston are also calculated. Combining the results of the measurements with the theoretical model for force calculation, a technique for estimating the actual running clearance of the piston is presented. A technique for deriving the displacement from the measured acceleration is developed. By representing the engine response in terms of displacement it is possible to recognise the applied force time history and thus the identification of the specific parts of the engine structure primarily excited by moments and by direct force. It is shown that the engine structure response is a transient phenomenon and is maximum in the vicinity of the applied force. The displacement technique for quantifying engine response provides detailed information of the distortion of the running engine enabling the prediction of mechanical inputs which control the turbocharged engine noise.

The success of theoretical engine noise prediction, using such techniques as finite element modelling, is highly dependent upon the understanding of the various mechanisms of noise generation in the running engine. The forcing mechanism of an operating engine is complicated as it involves a large number of forces taking place simultaneously or in rapid succession at various positions in the structure. A number of test methods have been developed to simulate individually each one of these loading mechanisms on non-running engines. These test methods are reviewed in this thesis with an objective judgement on their representation of the actual forcing on the running engine. A new hydraulic test method has been successfully developed to simulate various forms of loading mechanisms on the non-running engine like the gas force on top of the piston, main bearings axial and vertical loading, and piston slap force. This test method is shown to be more comprehensive, realistic, practical and representative than previous simulation techniques, especially with respect to the level of forcing which corresponds well with that of the running engine. The structural sensitivity of the engine has been evaluated for different representative loading, the most sensitive input being that of the axial force at the main bearings. The damping characteristics of a large six cylinder diesel engine block has been calculated and the crank shaft is shown to affect it as well as affecting the wave propagation through the structure. The simulation technique has also allowed the detailed study of the various forms of wave propagation in a diesel engine load carrying structrue and this has shown the importance of both bending and longitudinal travelling waves in noise radiation. It is shown that bending waves provide the maximum amplitudes of vibration, whereas longitudinal wave propagation allows for the fast transfer of energy through the structure which can then convert into bending waves with high noise radiation potential. Analysis of the results has shown that some doubt must be placed on the normal mode method for predicting the response in the lower frequency range, and an alternative model based on highly damped travelling bending waves is visualized to be suitable to model the crank case wall but not the stiff upper.

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This thesis describes how the overall noise of an engine design can be predicted using the finite element method together with a time integration technique for the prediction of the dynamic response. A novel method is presented which incorporates the A-weighting and radiation efficiency in the force such that the overall noise level can be predicted directly in the time domain. This method of noise prediction has been used, in conjunction with an automatic procedure for changing the surface boundary profile of an engine crankcase, to assess the overall noise level of a large number of possible shapes. A simple optimization algorithm has also been written to vary the block shape to produce the best design for low noise within practical constraints. Application of the above methods on a simple engine model have provided an experimental noise reduction of 5dB. It is shown that the weight of the engine is very little affected by quite substantial changes in crankcase shape.

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Dans le but de réduire la consommation en carburant, les émissions de CO2 et les polluants tout en maintenant le haut rendement des moteurs, de nouveaux modes de combustions ont été étudiés et sont d’excellents candidats pour remplacer les moteurs conventionnels. En particulier, le mode HCCI a montré une excellente aptitude pour répondre à ces objectifs. Néanmoins, en dépit de ses avantages, de nombreux challenges sont à surmonter avant de permettre le développement de tels moteurs. Parmi eux, obtenir un contrôle efficace de la totalité de ce processus de combustion sur un large domaine d’utilisation demeure le principal défi. Ces travaux de thèse s’intéressent à l’utilisation des espèces chimiques oxydantes comme un moyen robuste de contrôle de la combustion HCCI. En raison de ces fortes propriétés oxydantes, l’ozone a été la principale molécule étudié. De plus, son intérêt est renforcé par le fait que l’ozone peut être produit au sein d’un véhicule au moyen de petits générateurs, mais cela peut aussi produire des oxydes d’azote. Ces recherches ont été effectuées au moyen d’un banc moteur monocylindre HCCI et couplées avec des simulations de cinétique chimique. Les deux principaux objectifs ont été : (1) Evaluer le potentiel d’utilisation d’un générateur d’ozone pour contrôler la combustion HCCI. L’impact de plusieurs espèces chimiques oxydantes, ozone and NOx, a été étudié sur la combustion de l’isooctane. De plus, un contrôle dynamique a été mis en place avec succès. (2) Comparer l’influence de l’ozone sur la combustion de l’isooctane et de carburants alternatifs. Des carburants à forte teneur en méthane et des alcools ont été étudiés en raison de leur forte résistance à l’autoinflammation et de leur structure chimique. / To reduce the fuel consumption, CO2 emissions and pollutant emissions while keep improving thermal efficiency of engines, alternative combustion modes are being investigated as good candidates to replace spark-ignited and diesel engines. In particular, Homogeneous Charge Compression Ignition (HCCI) engines have proven their potential to meet these requirements. However, despite of these advantages, several challenges remain to be addressed prior to the widespread implementation of HCCI engines. Among them, the control of the overall combustion process in such an engine over the full operating range is still considered as the main challenge to overcome. The present work introduces the use of oxidizing chemical species seeded in the intake system as a robust control technique for HCCI combustion process. In particular, ozone was examined due to its strong oxidizing characteristics. Moreover, ozone can be easily produced on-board a real vehicle from the intake oxygen thanks to small ozone generators, but can also lead to the production of NOx. Investigations were carried out using a single-cylinder HCCI engine and kinetics computation analysis. The two main objectives of this work are: (1) Evaluate the potential of using ozone generator to control the HCCI combustion. Along these lines, the interaction between NOx and ozone was investigated for isooctane as fuel and a real time control of the HCCI combustion was implemented and successfully tested. (2) Compare the influence of ozone on the combustion of isooctane and alternative fuels. Methane-based fuels (methane/propane and methane/hydrogen mixtures) and alcohols (methanol, ethanol, n-butanol) were selected due to their higher resistance to autoignition and their different chemical structure.

Researchers are trying to find a solution for reducing the vibration of the engine with minimum changes to the engine mounts. Several researches and main giant car companies have presented valuable effort in these areas but still new research is needed to improve the control system. The present research carried out a comprehensive study of the state of art methods to suppress unwanted vibration from the engine to the passenger cars. This research was designed based on the objective of the Trelleborg Company to investigate the influence of Active Vibration Control (AVC) on the real engine. Therefore, this thesis tried to challenge the vibration problem with practical engineering approach by implementing different types of controllers experimentally and applying them on the real petrol engine. Inversing controlling technique and PID controller tuned with different methods (Ziegler Nichols and tyreus-luyben) have been tested here on two separate platforms; unbalanced DC motor and petrol engine. In addition, as a requirement of the study, the resonance frequency and related mode shapes of the system was investigated experimentally. It is also shown that using suitable filters can help elimination of high frequency noises in the control signals. This study experimentally tests PID controller with mentioned tuned methods on a real engine with this specific setup for the first time. A new scheme was developed with "mode shapes specific controller system", according to which the shaker position and the controller parameters were specified according to the system mode shapes. The result of applying controllers shows that both control methods have a similar effect on vibration reduction. A 33% - 37% reduction on DC motor achieved in different frequencies (20Hz, 37.5Hz and 46.2Hz) with different control methods, and about 10% reduction on petrol engine at resonance frequency while the shaker IV40 (with max 30N force) was placed on the chassis. For reducing the vibration transmitted from the engine to the chassis, for the first time the shaker was placed on the engine (unlike in previous studies where the shaker was placed on the chassis). Using shaker IV40 placed on the engine results in a 20% reduction in vibration transmission, which is a significant improvement in comparison with having the shaker on the chassis. The optimum result was achieved using shaker IV45 (Max 50N force), which yielded a vibration reduction of 33%.

In recent years, serious restrictions on diesel emission levels, combined with price instability and a significant increase in imports, has forced researchers to look for alternatives to this fossil fuel. Biodiesel is widely accepted as an alternative because it can be used in diesel engines without any substantial modifications and produced by sustainable resources. However, there are serious gaps in available knowledge regarding the effects of biodiesel blends on engine fuel injection systems and the engine combustion process. Therefore, this research focuses on the investigation into such effects through a vibration analysis of fuel injection systems in order to achieve nonintrusive quantitative diagnosis and hence condition monitoring of CI engines. Having identified the specifics of technique gaps by a comprehensive literature study, this research firstly, investigates the dynamics of the fuel injection system with a CI engine running on biodiesel blends as fuels. This is achieved by numerical modelling analysis and experimental studies, which paves ways for using vibration response of fuel injection to diagnose the dynamic behaviour of different fuel properties. Then it investigates the of the change dynamic behaviour of fuel injection on engine combustion process. Finally, it explores the diagnostics of engine valve train clearance faults with an engine running with biodiesel and biodiesel blends based on engine fuel injection vibration responses. A mathematical model has been developed and used to simulate the behaviour of the fuel injection system, including the fuel delivery and injector needle valve motions. It has concluded that the high pressure dynamic forces within the injection system will be affected by fuel properties such as fuel density, viscosity and bulk modules. The simulation results demonstrated; (i) that, the injector pressure is higher than that of the fuel injection pump, whose amplitudes are about 10% higher for biodiesels compared with petro-diesel; (ii) the levels of the pressure forces applied to the delivery valve and injector needle valve are also higher for biodiesel blends and (iii) nearly 1° (cam shaft) advance in the times of fuel injection rates and valve impacts with biodiesel and biodiesel blends. These predictions are confirmed by experimental results obtained by injection line pressures and pump vibrations and in-cylinder pressures. Diesel engines are particularly prone to the engine combustion process primarily due to a fault in the fuel injection system and an abnormal clearance valve train conditions. The high-signal to noise ratio pump vibrations obtained from the pump body can be easily used for detecting and diagnosing faults from fuel injections. In the meantime, the research has also established that the pump vibration signals can be also used to recognise valve train diagnostics with medium effort of signal processing. It has found that the vibration levels become higher, due to the faults as a consequence of additional fuel supply to compromise the loss of overall power caused by poor combustion performance on the cylinder with an increased valve clearance. Moreover, B20 and B40 exhibit the similar changes with that of petro-diesel in the proposed high frequency envelop amplitudes (HFEA) whereas B100 shows less increased values. However, the pressure measurements are not very clear in representing these small changes in valve clearances for both the exhaust and inlet valves. Compared with head vibration signals, which also can indicate the faults by a reduced level of vibration due to an effect combined reduced valve movement stroke with gas flow dampening, the pump vibration signals uniformly show the injection events and allow combustion uniformity between different cylinders to be diagnosed using a single transducer, whereas it may produce less accurate diagnosis by the head vibrations because of the close overlap of combustion and valve impact responses which needs complicated methods to be separated.

A study has been conducted into the causes of cycle by cycle variations in combustion within a spark ignition engine, the best measured engine parameter to use for its characterization, and the effects that: ignition timing, equivalence ratio, fuel type, throttle position and knock, have upon it. A Ricardo E6 single cylinder variable compression ratio research engine was instrumented to allow measurement of: cylinder pressure, temperatures, speed, load, fuel flow and air flow. The engine was also fitted with an optical slice that allowed optical access to the combustion chamber and enabled measurement of the early flame speed (up to 10 mm from spark plug gap) using a laser schileren system. Cylinder pressure data were collected on a dedicated HP1000 computer for every degree of crank angle rotation for up to 300 successive cycles. A phenomenological model was developed for turbulent combustion that split the combustion process into three phases: early laminar burn, turbulent combustion, and final burn. The model allowed the study of the physical phenomena occurring within the combustion chamber and enabled insights to be gained into their effects on combustion and cyclic variations. The study showed: The variation in mixture strength has a far greater effect on the average and Coefficient of Variation (COV) values of all the combustion performance parameters, than does changing the fuel type. Cycle by cycle variations in combustion are best characterized by COV of imep. The onset of knock has no discernible effect on the COVs of the measured parameters. The part throttle results show higher COVs than at Wide Open Throttle (WOT) due to slower burn, supporting the theory that faster initial flame speeds reduce cyclic variations. The combustion model was used to support the hypothesis that cycle by cycle variations are caused by movement of the flame kernel by turbulence within the combustion chamber.