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A mixed-lubrication model considering the oil supply was developed. The elastoplastic model was applied in the asperity contact simulation. The oil-film thickness at the ring-cylinder liner interface was determined using a mass conservation algorithm. The modeling results were compared with experimental results for verification on a reciprocating wear tester. It is found that, under the fully flooded condition, the results of the Greenwood-Trip model and the current model in the middle of the stroke are in accordance with the experimental results, but the results of the current model at the ends of the stroke are closer to the experimental results than the Greenwood-Trip model results are. Under the starved-lubrication condition, the friction coefficient of the current method is closer to the experimental result than that of the Greenwood-Trip model in the entire stroke. Therefore, the model developed in this study is appropriate for mixed lubrication under the fully flooded condition and the starved-lubrication condition. Furthermore, the model was applied to the ring pack of a diesel engine to study the effect of the oil supply on the tribological performance. The results show that the frictional forces under the 1 mm oil supply condition are far larger than those under the sufficient oil supply condition in the middle of the stroke, and so the increase in the frictional force may be used to identify scuffing failure in future studies if the relationships between the frictional forces and the measured vibration signals of the engine are obtained.

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Chemical sensing is of great importance in many application fields, such as medicine, environmental monitoring, and industrial process control. Distributed fibre-optic sensing received significant attention because of its unique feature to make spatially resolved measurements along the entire fibre. Distributed chemical sensing (DCS) is the combination of these two techniques and offers potential solutions to real-world applications that require spatially dense chemical measurements covering large length scales. This paper presents a review of the working principles, current status, and the emerging trends within DCS.

We propose and experimentally demonstrate a method to significantly extend the sensitive window of tilted fiber-Bragg grating (TFBG) into low-refractive-index region with the integration of graphene coating. The coupling between cladding modes of TFBG and graphene coating results in an obvious modification of the cladding-mode envelope, which provides a sensitive regime relying on graphene's complex refractive index. Interacting the graphene-coated TFBG with various aqueous solutions, we observe strongly enhanced sensitivity in the low-refractive-index region of 1-1.428, which is about 10-fold extended from that of the unloaded TFBG. The graphene-coated TFBGs present great potentials in the biochemical sensing window.

The method of lubrication for piston ring in some types of low-speed two-stroke marine diesel engines is completely different from those in medium- or high-speed diesel engines since the inner surface of cylinder liners are textured with elliptical grooves in macroscale and honing texture in microscale. In this paper, a numerical model has been developed to study the potential of use of cylinder bore surface texturing, in the form of circumferential oil grooves with different dimensions and densities, to improve the tribological properties of piston ring–cylinder liner tribosystem. The average Reynolds equation has been employed in the area of microscale texture and the effect of macroscale grooves has been incorporated to improve the currently lubrication model. The focus is put on cavitation formation condition and boundary condition in grooves within the area of lubrication, analysis of the effect of macrogroove dimension characters and distribution of grooves on the tribological performance of piston compression ring. The solution provides the hydrodynamic friction force, boundary friction force, coefficient of friction, and the total friction force. The results show that the cylinder liner oil grooves can efficiently be used to maintain hydrodynamic effect. It is also shown that optimum surface texturing may substantially reduce the friction losses between piston ring and cylinder liner.

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The piston ring is one of the most important parts of a two-stroke marine diesel engine. It is lubricated by a special mode in which the lubricating oil is directly injected into the liner’s inner surface. In this article, taking account of the oil supply, a piston ring lubrication model is developed based on oil mass conservation. The lubrication region of this piston ring–cylinder liner is divided into inlet, core lubrication, and outlet regions, with the oil supply being converted into an oil film. The impact of the width of the core lubrication region on squeezing of the oil is considered. To verify the model, friction force measurements are performed in a reciprocating bench test under fully flooded conditions, and the model is further validated by comparing the minimum oil film thickness with data from the literature. The model is applied to the top ring of a two-stroke marine diesel engine, and the impacts of the oil supply and its design parameters are analyzed.