90 research outputs found

    Machine Learning for Nondestructive Wear Assessment in Large Internal Combustion Engines

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    Digitalization offers a large number of promising tools for large internal combustion engines such as condition monitoring or condition-based maintenance. This includes the status evaluation of key engine components such as cylinder liners, whose inner surfaces are subject to constant wear due to their movement relative to the pistons. Existing state-of-the-art methods for quantifying wear require disassembly and cutting of the examined liner followed by a high-resolution microscopic surface depth measurement that quantitatively evaluates wear based on bearing load curves (also known as Abbott-Firestone curves). Such reference methods are destructive, time-consuming and costly. The goal of the research presented here is to develop nondestructive yet reliable methods for quantifying the surface condition. A deep-learning framework is proposed that allows computation of the bearing load curves from reflection RGB images of the liner surface that can be collected with a wide variety of simple imaging devices, without the need to remove and destroy the investigated liner. For this purpose, a convolutional neural network is trained to predict the bearing load curve of the corresponding depth profile from the collected RGB images, which in turn can be used for further wear evaluation. Training of the network is performed using a custom-built database containing depth profiles and reflection images of liner surfaces of large gas engines. The results of the proposed method are visually examined and quantified considering several probabilistic distance metrics and comparison of roughness indicators between ground truth and model predictions. The observed success of the proposed method suggests its great potential for quantitative wear assessment on engines during service directly on site

    Tribology in Marine Diesel Engines

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    This chapter deals with the tribology of marine diesel engines. Several types of diesel engines have been installed and used in the engine room of marine ships. Some of them, used for propulsion, operate at low-speed in a two-stroke combustion process in conjunction with propellers. Four-stroke engines are used for power generation and operates at medium-speed. In general, two or more four-stroke engines, including spares, are installed in the large ships. Tribological problems are important issue in the respect of reliability in the marine diesel engines, and there are many tribological engine components including bearings, pistons, fuel injection pumps and rollers. Moreover, the marine engines have lubricant problems such as lacquering. Improvements to the tribological performance of marine engine components, and lubricants can provide reduced oil and fuel consumption, improved durability, increased engines power outputs and maintenance. Therefore, this chapter shows better designs and methods in order to improve the tribological problem in the marine diesel engines

    Measurement and prediction of in-cylinder friction in internal combustion engines

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    Currently, nearly 75% of worldwide transport is powered by internal combustion engines, with the worldwide transport sector accounting for 14% of the world’s greenhouse gas emissions. With the current trend of downsizing and reducing vehicle cost, expensive solutions such as hybrids are often not viable. One solution is to reduce engine parasitic losses, thereby indirectly improving fuel efficiency, hence emissions. In terms of frictional losses, the piston-cylinder system accounts for 50% of all such losses, which altogether contribute to 20% of all engine losses. The thesis describes an efficient analytical-numerical model in terms of computation times and CPU requirements. The model is a one dimensional analytical solution of Reynolds equation using Elrods cavitation algorithm. The model also includes determination of viscous friction as well as boundary/asperity friction based on the work of Greenwood and Tripp. Lubrication rheology is adjusted for generated hydrodynamic pressures and measured conjunctional temperature based on the cylinder liner. Model predictions are supported by a range of experimental work, from basic science measurements using an instrumented precision slider bearing rig for direct measurement of friction to the development and use of a floating liner on a motored and fired high speed, high performance internal combustion engine at the real situation practical level. The thesis highlights the development of the experimental rigs/engines as well application of state of the art instrumentation and data processing. The combined numerical and experimental analysis show that a significant proportion of friction takes place at the top-dead-center reversal in the transition from the compression to the power stroke. Under motored conditions with low in-cylinder pressures this appears to follow Poiseuille friction, whereas under fired conditions with higher in-cylinder pressures causing increased compression ring sealing a mixed and/or boundary regime of lubrication is observed and predicted. Other than at the TDC reversal in both motored and fired conditions the frictional characteristics follow in direct proportion to the piston sliding velocity, therefore showing the dominance of viscous friction. One outcome of the thesis is a validated analytical model which due to its computational efficiency can now be used in industry to provide timely predictions for the compression ring contact zone. Most significantly, the thesis has established an experimental procedure, infrastructure and data processing methods which enable the determination of the regime of lubrication and the underlying mechanisms of friction generation from basic science sliding surfaces to in situ direct measurements from a fired engine at high loads and sliding speeds

    The detection of adhesive wear on cylinder liners for slow speed diesel engine through tribology, temperature, eddy current and acoustic emission measurement and analysis

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    PhD ThesisThe research concerns the condition monitoring of cylinder liner of large bore diesel engines using various methodologies to identify the onset of scuffing. The reasons of scuffing, improved designs and operational processes to prevent its occurrence were discussed. The research focused on modeling the normal condition of the cylinder liner with sufficient lubrication and detecting the precursor of scuffing by reducing the lubrication. The four detection systems used on the test facilities and field tests of the cylinder liners used tribology, temperature sensor, eddy current sensor and acoustic emission sensor. Experimental assessment of eddy current sensor was conducted for insufficient lubricating oil conditions for different cylinder liner wall pressures using a specially designed test facility. Field tests of temperature sensor and eddy current sensor were carried out on a 800mm bore worn cylinder liner of a container ship in service. Field test of acoustic emission sensor was carried out on a high speed automobile engine. Scuffing detection by temperature sensing should be considered as the last safety barrier, as it registers the after effect of scuffing and solely depends on the localized condition and the material’s thermal status. Mounting eddy current sensors are considered intrusive. Four sensors per cylinder are needed, which are prone to damage by the rings when the liner wears out. Additionally, the sensors measure only small section of the rings and their lubrication condition. Acoustic emission analysis effectively detects onset of scuffing on the cylinder liners and the rings. Initial findings from the lab and the field test on a four stroke engine confirmed this. However, more field tests under various loading condition on a slow speed engine is needed to understand the various event alignment and the non-routine detection, such as scuffing. They can be coupled with thermocouples to serve as a secondary protection

    Tribological optimisation of the internal combustion engine piston to bore conjunction through surface modification

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    Internal combustion (IC) engines used in road transport applications employ pistons to convert gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38- 51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to 1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a direct impact on specific performance and / or fuel consumption. In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently, these engines have a shorter useful life and a high premium is placed on measures which would increase the output power without further reducing engine life. Reduction of friction offers such an opportunity, which may be achieved by improved tribological design in terms of reduced contact area or enhanced lubrication or both. However, the developments in the motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc reliance, based upon a limited number of actual engine tests in order to determine if any improvement can be achieved as the result of some predetermined action. A representative scientific model generally does not exist and as such, investigated parameters are often driven by the supply chain with the promise of improvement. In cylinder investigations are usually limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the lubricant employed. Of these investigated areas newly emerging surface coatings are arguably seen as predominate. This thesis highlights a scientific approach which has been developed to optimise piston-bore performance. Pre-existing methods of screening and benchmarking alterations have been retained such as engine testing. However, this has been placed in the context of validation of scientifically driven development. A multi-physics numerical model is developed, which combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic tribological framework. Experimental tests were performed to validate the findings of numerical models. These tests include film thickness measurement and incylinder friction measurement, as well as the numerically-indicated beneficial surface modifications. Experimental testing was performed on an in-house motored engine at Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at Loughborough University, as well as on other engines belonging to third party clients of Capricorn. The diversity of tests was to ascertain the generic nature of any findings. The multi-physics multi-scale combined numerical-experimental investigation is the main contribution of this thesis to knowledge. One major finding of the thesis is the significant role that bulk thermo-structural deformation makes on the contact conformity of piston skirt to cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction

    Advances and Trends in Non-conventional, Abrasive and Precision Machining

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    The work included in this book pertains to advanced abrasive and nonconventional machining processes. These processes are at the forefront of modern technology, with significant practical significance. Their importance is also made clear by the case studies that are included in the research that is presented in the book, pertaining to important materials and high-end applications. However, the particularities of these manufacturing processes need to be further investigated and the processes themselves need to be optimized. This is conducted in the presented works with significant experimental and modeling work, incorporating modern tools of analysis and measurements

    THE INVESTIGATION INTO THE CONDITION MONITORING OF TRIBOLOGICAL BEHAVIOUR BETWEEN PISTON RING AND CYLINDER LINER USING ACOUSTIC EMISSIONS

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    To improve engine operational performance and reliability, this study focuses on the investigation into the behaviour of tribological conjunction between the ring - liner based on a comprehensive analysis of non-intrusive acoustic emission (AE) measurement. Particularly, the study will provide more knowledge of using AE for online monitoring and diagnosing the performances of the conjunction. To fulfil this study, it integrates analytical predictions of the theoretical modelling for the AE generation mechanism with extensive experimental evaluations. Moreover, effective signal processing techniques are implemented with a combination of the model based AE predictions to extract the weak and nonstationary AE contents that correlate more with the tribological behaviour. Based on conventional tribological models, tribological AE is modelled to be due to two main dynamic effects: asperity-asperity collision (AAC) and fluid-asperity interaction (FAI), which allows measured AE signals from the tribological conjunction to be explained under different scenarios, especially under abnormal behaviours. FAI induced AE is more correlated with lubricants and velocity. It presents mainly in the middle of engine strokes but is much weaker and severely interfered with AEs from not only valve landings, combustion and fuel injection shocks but also the effect of considerable AACs due to direct contacts and solid particles in oils. To extract weak AEs for accurately diagnosing the tribological behaviours, wavelet transform analysis is applied to AE signals with three novel schemes: 1) hard threshold based wavelet coefficients selection in which the threshold value and wavelet analysis parameters are determined using a modified velocity of piston motion which has high dependence on the AE characteristics predicted by the two models; 2) Adaptive threshold wavelet coefficients selection in which the threshold is gradually updated to minimise the distance between the AE envelopes and the predicted dependence; and 3) wavelet packet transform (WPT) analysis is carried out by an optimised Daubechies wavelet through a novel approach based on minimising the time and frequency overlaps in WPT spectrum. Based on these optimal analyses, the local envelope amplitude (LEA) and the average residual wavelet coefficient (ARWC) are developed from AE signals as novel indicators to reflect the tribological behaviours.\ud Both the hard threshold based LEA and wavelet packet transform LEA values allow two different new lubricants to be diagnosed in accordance with model predictions whereas they produce less consistent results in differentiating the used oil under several operating conditions. Nevertheless, ARWC can separate the used oil successfully in that it can highlight the AAC effects of particle collisions in used oils. Similarly, LEA shows little impacts of two alternative fuels on the tribological behaviours. However, ARWC shows significantly higher amplitudes in several operating conditions when more particles can be produced due to unstable and incomplete combustions of both the biodiesel and FT diesel, compared with pure diesel, indicating they can cause light wear

    Tribology of Machine Elements

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    Tribology is a branch of science that deals with machine elements and their friction, wear, and lubrication. Tribology of Machine Elements - Fundamentals and Applications presents the fundamentals of tribology, with chapters on its applications in engines, metal forming, seals, blasting, sintering, laser texture, biomaterials, and grinding

    Monitoring of the piston ring-pack and cylinder liner interface in diesel engines through acoustic emission measurements

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    Investigation of novel condition monitoring systems for diesel engines has received much recent attention due to the increasing demands placed upon engine components and the limitations of conventional techniques. This thesis documents experimental research conducted to assess the monitoring capabilities of Acoustic Emission (AE) analysis. In particular it focuses on the possibility of monitoring the piston ring-pack and cylinder liner interface, a critical engine sub-system for which there are currently few practical monitoring options. A series of experiments were performed on large, two-stroke and small, four-stroke diesel engines. Tests under normal operating conditions developed a detailed understanding of typical AE generation in terms of both the source mechanisms and the characteristics of the resulting activity. This was supplemented by specific tests to investigate possible AE generation at the ring-pack/liner interface. For instance, for the small engines measures were taken to remove known AE sources in order to accentuate any activity originating at the interface whilst for the large engines the interfacial conditions were purposely deteriorated through the removal of the lubricating oil supply to one cylinder. Interpretation of the results was based mainly upon comparisons with published work encompassing both the expected ring-pack behaviour and AE generation from tribological processes. This provided a strong indication that the source of the ring-pack/liner AE activity was the boundary frictional losses. The ability to monitor this process may be of significant benefit to engine operators as it enhances the diagnostic information currently available and may be incorporated into predictive maintenance strategies. A further diagnostic technique considered was the possibility of using AE parameters combined with information of crankshaft speed fluctuations to evaluate engine balance and identify underperforming cylinders.EU Competitive and Sustainable Growth Programme, Project no: GRD2-2001-5001

    Investigation into the dynamic responses and tribological characteristics of cylinder liners in a IC engine with alternative fuels

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    Promoted by the realisation of dwindling fossil fuel supplies and their adverse environmental impacts, there more and more types of alternative fuels to fossil diesel have been used and investigated in compression ignition engines. However, the majority of researches on alternative fuels mainly focus on their power performance, efficiency and emission performance, without fully investigating the potential effects on the vibro-acoustic emissions and tribological characteristics of engines caused by their significant differences in physical and chemical properties. Consequently, the impacts of long-term use of alternative fuels on structural failure, lubrication degradation, friction aggravation, overall service life spans and associated maintenance activities of internal combustion (IC) engines have not yet been fully understood. To reduce this gap this thesis focuses on the investigation into the vibration responses of cylinder liners in a diesel engine to accurately characterises the tribological behaviour between the piston rings and cylinders which is one of the most decisive sub-processes that determine engine performance and yet is correlated with the combustion of different fuels. In particular, the investigation was carried out by coupling the hydrodynamic lubrication model with structural vibration effects through a series of extensive numerical simulations and systematic experimental evaluations in order to establish a vibration based technique to monitoring tribological behaviour and thereby accurately assess the influence. Based on the dynamic coupling mechanisms between the combustion characteristics of alternative fuels and the tribological behaviours of cylinder liners, the most significant influences from the fuel burning on tribological behaviour of cylinder liners concerned in this study is a direct and physical approach such as the effect of liner vibrations on cylinder friction process, even though an indirect and chemical but very slow approach such as the deterioration of oil properties by combustion products can happen. To characterise the direct influence a finite element dynamic model was developed and validated for predicting the dynamic responses of cylinder liners to respective excitation sources including the highly nonlinear combustion pressure shocks and subsequent piston slap impacts. The realistic consideration of both the characteristics of structural modes up to 15kHz and nonlinearities of elastic assembly constraints allows obtaining accurate prediction that the combustion shocks cause vibrations in a frequency range around 10kHz with an amplitude order of 0.01μm, whereas the piston slaps in frequency range from 1k to 5kHz with an amplitude order 0.2μm, which gives a clear and quantitative indication of the nonlinear phenomena of liner vibration due to combusting alternative fuels and varying lubrication conditions. In addition, a decomposition analysis of piston side-thrust forces provides more insight of the localized response characteristics corresponding to coupling interactions of combustion force with inertia force of piston assembly. To further investigate the potential influences of structural deformations to tribological behaviours of cylinder assemblies, a new dynamic deformation based lubrication model was developed based on an employment of improved shearing factors in which the effect of inevitable liner vibrations is included to obtain a more realistic lubricating film formation, distribution and tribological behaviours. The simulation studies show that this advancement in modelling oil films predicts that the biodiesel with more intense vibration emissions is able to reduce the friction loss between pistons and liners, whereas the methanol-diesel blend with weakened liner dynamic response may exacerbate the friction loss of IC engines. This finding confirms further that the vibration responses allow a straightforward and in-depth indication of the effect generated by using different fuels. In addition, a further experimental investigation was carried out based on a motoring engine test, in which high frequency sinusoidal vibrations at 25 kHz, 30 kHz and 40 kHz are added to the external surface of the linear. The observable changes in motoring torque verify that proper external vibrations can affect the tribological behaviours between the pistons and liners, including both asperity friction and viscous friction, and resulting in the friction reduction of IC engines. Particularly the 40 kHz vibration at the maximal driving power of the test device can achieve a reduction of 1.79% in the motoring torque. This has demonstrated more on the effectiveness of this vibration based diagnostic method in assessing the influences of alternative fuels upon tribological behaviours of piston ring and cylinder liners. Finally, further researches on the subjects is also proposed in order to complete the vibration based diagnostics in achieving more accurate assessment of engine lubrication conditions and effective friction reduction
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