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The emissions control regulations introduced by governments are set to improve engine quality and reduce the impact automobiles have on the planet. The regulations imposed on the manufactures have proven very difficult to meet. To this effect some of the leading names in the industry were pushed to invest significant funding in research, development and optimisation of combustion, powertrain and tribology inside the ICE. Their goal is reduction of fuel consumption and emissions while increasing performance and durability. The piston-ring and cylinder-liner interaction is the major source of frictional losses for reciprocating ICEs and so, it is important to avoid any failure of piston-rings to effectively control lubricant transport from the sump onto the cylinder walls and further to the combustion chamber. This lubricant will participate in the emissions through absorption and desorption of fuel in the oil film at the cylinder walls, also resulting in lubricant contamination and consumption. The objective of this project is to assist with the investigation of phenomena occurring in the cylinder liner and piston-ring interaction under different operating conditions. The following investigations have been carried out, flow and cavitation visualisation in a model lubricant rig and cavitation visualisation in a newly designed optical engine.

Both in engines and test rigs, cavitation in piston-ring lubrication is a subject studied by many researchers in the past. Although there is no sufficient evidence of cavitation erosion on the surface of the liner, this phenomenon is studied as part of the lubricant transport process. During the transport process the lubricant enters the combustion chamber. The combustion products of consumed oil might contribute to exhaust gas emissions and with emission legislation becoming more stringent, it is important that oil consumption is reduced to the lowest level possible. The role of the piston-rings is becoming more complex with the imposed requirements for lower oil consumption and friction. The piston-ring pack role on engine performance, durability and wear, is becoming on the other hand, more demanding. Between the piston-ring and cylinder liner, cavitation occurs as a result of two-phase liquid flow. Cavitation has long been recognized to degrade performances in most engineering applications and its effect in piston-ring lubrication is that it alters the oil film pressure profile, generated at the converging-diverging wedge of the piston-ring. An area of the piston-ring surface is void, corresponds to subatmospheric pressures and thus, the piston-ring load capacity is altered. Two experimental rigs were used, a simplified single-ring test rig that simulates the piston-ring liner movement at speeds corresponding to idle but the movement is reversed and a single cylinder diesel engine that was used for visualization results only, after the necessary modifications.

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication single-ring test rig and oil transport and cavitation visualisation in custom made cylinder assemblies of optical engines are the tools used to quantify the transport process under the piston ring and cylinder liner. Simplification of the interface is an essential technique that enhances the researcher's confidence in results interpretation. Engine complexity and severe oil starvation are impeding the analysis of the experimental results. Visualisation experiments constitute an effective way to test various lubricant types and assess their overall performance characteristics, including their properties and cavitation behaviour. The repeatability of the visualisation method establishes the parametric study effects and offers valuable experimental results. As a further step towards the lubricant composition effect, a link between the lubricant formulation and the operating conditions could be established as the oil performance is assessed with a view to its transport behaviour. Image processing is used to quantify the impact of cavitation on piston ring lubrication in conjunction with varied operating and lubricant parameters. The characteristics of the lubricant and the working environment have an impact on these types of cavities. Viscosity, cavitation, oil film thickness (OFT), lubricant shear-thinning characteristics and friction are all linked. [ABSTRACT FROM AUTHOR]

The lubricated interface at the piston-ring and liner and its interaction with different lubricants and testing conditions is examined in terms of experimental measurements that show the minimum oil film thickness developed at the lubricated or depending on conditions partly lubricated conjunction and the surface interaction intensity, as measured from the friction sensor. An analysis is carried out with the use of different parameters for the experiments as well as different lubricants in a simplified piston-ring simulation test rig. This analysis is further enhanced with the squeeze film effect investigations close to the stroke reversals and together with cavitation initiation and load-carrying effect results from previous experimental data, light is shed on the interacting surface's behaviour at the different lubrication regimes. Another parameter, the viscosity index of the lubricant is used as an indication of the effects of squeeze film shift and friction force measurements and how the load and temperature effect are influencing the squeeze film. [ABSTRACT FROM AUTHOR]

The well-established oil condition monitoring tool of spectrometric oil analysis is used to expand previous published experimental analysis with a view to enhancing multiple wear metal elements study in numerous different applications. This study includes gas turbine engines, piston engines, turboprop and turboshaft engines and helicopter gearbox assemblies. The database used in the original study was enhanced with numerous applications that were used to establish the credibility of spectrometric oil analysis as an important diagnostic tool. The importance of the method lies in its ability to locate unusual concentrations of a metal element that is translated as an indication of abnormal wear of the equipment under scrutiny. The operator benefits from major failures avoidance and taking correct decisions regarding equipment maintenance and servicing or repairing, can also profit from economic factors rationality during equipment operation. Lubricant quality, identification or imminent failures, prolonged life cycle and acquisition of statistical data are conditions that emanate from the correct interpretation of the results that in turn, can avoid human lives and equipment losses due to major incidents. [ABSTRACT FROM AUTHOR]

The laser-induced fluorescence technique is based on the excitation of molecules of a fluorescent material by a light source. The main advantage of this technique is that it has the potential to quantify the lubricant film thickness throughout the cycle. Similar to all the other optical techniques, it has this major advantage compared to the electrical techniques where the oil film can be measured only under the piston rings. In this work, experimental data from a simulating single-ring test rig are presented and further parametric analysis is given regarding cavitation in lubricants that was, at first, in the case of the single-ring test rig, evident in laser-induced fluorescence measurements. Different lubricants are used for the laser-induced fluorescence experiments and the different laser-induced fluorescence signals are analysed and interpreted compared to their physical and chemical properties and, furthermore, with the aid of imaging through a glass liner, a clearer picture is given regarding the cavitation shapes together with the respective laser-induced fluorescence measurements and cavitation initiation. [ABSTRACT FROM AUTHOR]

Oil film pressure, the driving force behind piston-ring lubrication phenomena, is measured in a single piston-ring simulating rig after the successful installation of a miniature pressure transducer. The partition of overall load-carrying capacity between direct surface interaction and hydrodynamic action is clearly of some significance if the characteristics of the piston seal are to be understood and predicted with any confidence. It is therefore important that the contribution of the fluid film lubrication to load support be adequately represented. This study presents an extensive load, speed, temperature and piston-ring curvature parametric study on how the measured pressure profile at mid-stroke is affected in terms of peak pressure, magnitude and shift in the trailing edge of the piston ring, taking into account cavitation appearance and lubricant viscosity variation. [ABSTRACT FROM AUTHOR]