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Title: Reducing in-cylinder parasitic losses through surface modification and coating
Authors: Howell-Smith, S.J.
Rahnejat, Homer
King, P.D.
Dowson, D.
Keywords: Piston–cylinder system
Parasitic losses of the engine
Laser surface texturing
Hard wear-resistant coatings
Issue Date: 2014
Publisher: © IMechE
Citation: HOWELL-SMITH, S.J. ... et al., 2014. Reducing in-cylinder parasitic losses through surface modification and coating. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 228 (4), pp. 391 - 402.
Abstract: Friction constitutes nearly one fifth of all engine losses. The main contributory source of frictional losses in most engines is the piston-cylinder system, accounting for nearly half of all the parasitic losses. Minimisation of this is essential for improved fuel efficiency and reduced emissions, which are the main driving forces in engine development. The tribology of piston-cylinder conjunctions is, however, transient in nature. This means that various palliative actions need to be undertaken to suit certain instances during the engine cycle. In general, formation of a coherent film of lubricant of suitable viscosity reduces the chance of boundary interactions for most of the piston cycle. Plateau honing of the cylinder bore surface reduces the 'peakiness' of the surface topography. Furthermore, if regularly spaced grooves are provided on the contacting surface, these grooves can act as reservoirs of lubricant. However, at low sliding speeds, which are typically found during piston motion reversals, lubricant entrainment into the contact either ceases or is significantly reduced. Therefore, at the end of the piston strokes, there is a greater chance of boundary interactions, resulting in increased friction. There is a need to engineer the surface topography in these low-relative-speed regions in a manner conducive to the retention of a lubricant film. Surface texturing by means of laser processing or mechanical indentation at the dead centres are used to produce local reservoirs of lubricant as well as to encourage and direct the flow of lubricant into the contact conjunction. The paper shows that such surface-modifying features improve the engine's output power by as much as 4% over that of the standard cylinder bore surface. To reduce wear and scuffing, particularly at the top dead centre, hard coatings can also be used. However, smooth surfaces and the generally oleophobic nature of hard coatings can increase the chance of adhesion, particularly at low sliding speeds. This means that prevention of wear does not necessarily lead to improved fuel efficiency. Furthermore, it is necessary to determine the geometry of the textured patterns in order to avoid the leakage of oil from the ring-pack conjunctions, which can result in increased emissions as well as lubricant degradation and depletion. © IMechE 2014.
Description: This is an author produced version of a paper published in Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. Uploaded in accordance with the publisher's self-archiving policy. The definitive version is available at: https://doi.org/10.1177/0954407013512626
Sponsor: This work was supported by the Engineering and Physical Sciences Research Council under an Encyclopaedic Program Grant as well as by Capricorn Automotive Ltd
Version: Accepted
DOI: 10.1177/0954407013512626
URI: https://dspace.lboro.ac.uk/2134/25726
Publisher Link: http://dx.doi.org/10.1177/0954407013512626
ISSN: 0954-4070
Appears in Collections:Published Articles (Mechanical, Electrical and Manufacturing Engineering)

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