Capricorn Automotive Ltd

Basingstoke, United Kingdom

Capricorn Automotive Ltd

Basingstoke, United Kingdom

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Chong W.W.F.,Loughborough University | Howell-Smith S.,Capricorn Automotive Ltd | Teodorescu M.,University of California at Santa Cruz | Teodorescu M.,Cranfield University | Vaughan N.D.,Cranfield University
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2013

The article proposes a mathematical model, which predicts the frictional performance of an internal combustion engine compression ring in the vicinity of the top dead center region. It accounts for the blow-by induced inter-ring pressures drop and for the cavitation region at the trailing edge of the contact. The model is used to predict the behaviour of both new and worn compression rings for wide open throttle operating conditions. It is shown that the wear of the ring profile increases the oil film thickness decrease the frictional losses and significantly reduces the extent of the cavitation region. © IMechE 2012.


Morris N.,Loughborough University | Leighton M.,Loughborough University | De La Cruz M.,Loughborough University | Rahmani R.,Loughborough University | And 2 more authors.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2015

Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved micro-wedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions. © IMechE 2014.


Shahmohamadi H.,Loughborough University | Mohammadpour M.,Loughborough University | Rahmani R.,Loughborough University | Rahnejat H.,Loughborough University | And 2 more authors.
Tribology International | Year: 2015

Prediction of load capacity and friction depends on the assumed boundary conditions. The inlet comprises swirl and counter flows, admitting only a portion of the inward flow into the conjunctional gap. At the contact exit, the lubricant film ruptures with multi-phase flow through a cavitation region. Therefore, the boundary conditions affect the load carrying capacity and friction. A Navier-Stokes solution of multi-phase flow, including vapour transport is presented, with determined realistic boundary conditions. The evaluated boundaries agree with potential flow analysis satisfying compatibility conditions, not hitherto reported in literature. The investigation is extended to the determination of optimum compression ring contacting geometry. © 2015 The Authors. Published by Elsevier Ltd.


Gore M.,Loughborough University | Theaker M.,Loughborough University | Howell-Smith S.,Capricorn Automotive Ltd | Rahnejat H.,Loughborough University | King P.D.,Loughborough University
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2014

Piston-cylinder interactions account for a significant portion of frictional losses in an internal-combustion engine. This is mainly as the result of significant changes in the operating conditions (the load, the speed and the temperature) as well as the contact geometry and the encountered topography during a typical engine cycle. These changes alter the regime of lubrication which underlies the mechanisms of friction generation. The multi-variate interactive nature of the problem requires quite complex analyses which do not fully replicate the actual in-situ conditions. Therefore, there is a need for direct measurement of cyclic friction under controlled conditions. The paper describes the use of a novel floating-liner arrangement which is capable of direct measurement of friction, its transitory mechanisms, as well as determination of the regime of lubrication. © IMechE 2013.


Howell-Smith S.,Capricorn Automotive Ltd | Rahnejat H.,Loughborough University | King P.D.,Loughborough University | Dowson D.,Loughborough University | Dowson D.,University of Leeds
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2014

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.


Littlefair B.,Loughborough University | Howell-Smith S.,Capricorn Automotive Ltd. | Rahnejat H.,Loughborough University | Theodossiades S.,Loughborough University
Proceedings of the Spring Technical Conference of the ASME Internal Combustion Engine Division | Year: 2012

The in situ profiles of the piston skirt and cylinder bore surface are subject to thermo-elastic global deformation due to differential operating temperatures and forces1. In operation, a lubricant film is entrained into and pressurized within the gap between these profiles. This film not only supports the prevailing contact load, but also inhibits direct interaction of surfaces, thus reducing friction and thereby improving fuel efficiency. The reduction of reciprocating mass in motorsport applications has been achieved through the use of partial circumferential skirts for a number of years now. The response of the shape to both mechanical and structural loadings differs from the classic full circumferential skirt studies. This paper provides a 'snapshot' into how the inherent piston side load is supported by the piston skirt. It highlights the importance of the operational temperature on the skirt profile, conjunctional gap and the lubricant film. Additionally, it shows how a given piston skirt shape and its structural stiffness perform in operation. Copyright © 2012 by ASME.


Morris N.,Loughborough University | Rahmani R.,Loughborough University | Rahnejat H.,Loughborough University | King P.D.,Loughborough University | Howell-Smith S.,Capricorn Automotive Ltd.
Journal of Tribology | Year: 2016

Minimization of parasitic losses in the internal combustion (IC) engine is essential for improved fuel efficiency and reduced emissions. Surface texturing has emerged as a method palliating these losses in instances where thin lubricant films lead to mixed or boundary regimes of lubrication. Such thin films are prevalent in contact of compression ring to cylinder liner at piston motion reversals because of momentary cessation of entraining motion. The paper provides combined solution of Reynolds equation, boundary interactions, and a gas flow model to predict the tribological conditions, particularly at piston reversals. This model is then validated against measurements using a floating liner for determination of in situ friction of an engine under motored condition. Very good agreement is obtained. The validated model is then used to ascertain the effect of surface texturing of the liner surface during reversals. Therefore, the paper is a combined study of numerical predictions and the effect of surface texturing. The predictions show that some marginal gains in engine performance can be expected with laser textured chevron features of shallow depth under certain operating conditions. © 2016 by ASME.


Burbridge D.J.,Cranfield University | Howell-Smith S.,Capricorn Automotive Ltd. | Teodorescu M.S.,Cranfield University
Proceedings of the ASME Design Engineering Technical Conference | Year: 2011

Load bearing conjunctions are never perfectly flat. They are covered by surface features, which may be either unintentional roughness inherent in the manufacturing process or a combination of such roughness with intentionally introduced surface texture. In either case, only a small proportion of load bearing surfaces are in contact and carry load. This depends on the surface topography, material properties and contacting conditions. Simple surface roughness characterisation parameters such as Ra, Rp etc. although commonly used do not give an adequate description, particularly where surfaces are deliberately textured. Furthermore Imaged surface topographies commonly exhibit features below the resolution of the imaging apparatus. We demonstrate the application of a fractal geometry analysis to honed internal combustion engine cylinder liners, imaged by Atomic Force Microscopy and Confocal Laser Scanning Microscopy. This method enables anisotropic surfaces to be characterised by five parameters which can then be used to generate model surfaces whose characteristics follow very closely those of the measured surface. Analysis of the structure function allows the determination of length scales and roughness features relevant at a given contact length. The reconstruction of anisotropic surfaces is demonstrated. Results from modelled contacts between these surfaces reveal the likely asperity contact geometry to be used in modelling contact and friction in these interfaces. Copyright © 2011 by ASME.


Littlefair B.,Loughborough University | De La Cruz M.,Loughborough University | Theodossiades S.,Loughborough University | Mills R.,University of Sheffield | And 3 more authors.
Tribology Letters | Year: 2014

Advanced piston technology for motorsport applications is driven through development of lightweight pistons with preferentially compliant short partial skirts. The preferential compliance is achieved through structural stiffening, such that a greater entrainment wedge is achieved at the skirt's bottom edge through thermo-elastic deformation, whilst better conforming contact geometry at the top of the skirt. In practice, the combination of some of these conditions is intended to improve the load-carrying capacity and reduce friction. The approach is fundamental to the underlying ethos of race and high-performance engine technology. Contact loads of the order of 5 kN and contact kinematics in the range 0-35 m/s result in harsh transient tribological conditions. Therefore, piston design requires detailed transient analysis, which integrates piston dynamics, thermo-elastic distortion and transient elastohydrodynamics. The paper provides such a detailed analysis as well as verification of the same using noninvasive ultrasonic-assisted lubricant film thickness measurement from a fired engine under normal operating conditions, an approach not hitherto reported in literature. Good agreement is noted between measured film thickness and predictions. © The Author(s) 2013.

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