Effect of Carbon Coating on Scuffing Performance in Diesel Fuels

Abstract

The & l-has-van Alphen (dI-ivA)signal of the organic superconductor 13''-(BEDlTF)#SFsCHjCF$ 03O3 shows an inverse-sawtooth wave form which proves the existence of an ideal two-tlmensiond (2D) Fermi surface. The dHvA wave shape cartalmost perfectly be describedby a 2D theosy assuming a constantchemicatpotential. TMseither impIiesthe existence of the predictedquasi-one-dimensional band with an exceptionallylarge densi[yof statesor the chemical potentialmaybe pinneddue to locatized states nearthe Fermienergy.Keywords: Organic superconductors. M~gnetic measurements Organic metals of the type {BEDT-TTF)zX, where BEDT-TTF is bkethyletdthio-tetrathiafulvalene and X represents a monovalent anion, are characterized by their pronounced two-dimensional (2D) electronic structure with, often, negligible dispersion perpendicular to the highly conducting planes [1]. Nevertheless. the de Haas-van Aiphen (dHvA) oscillations in most of these high-quality metals exhibit only minor deviations from the conventional 3D Lifshitz-Kosevich (LK) theory [2]. This is in contrast to magnetoresistance oscillations where in a number of organic metals strong apparent deviations of the Shubnikovde Haas (SdH) signal fkom IX behavior have beersreported (see references in [3]). In transportdata, however, complicated scattering mechanisms are involved and a non-trivial tensor inversion is needed to extract the true SdH signaL Here, we report on true thermodynamic dHvA data which provide experimental evidenee for the existence of a perfeet 2D Fermi liquid in a bulk 3D organic metal.The highquaiity $-(BEDT-T'IT9ZSF5CH2CFZS03 single crystals were grown by cketrocrysb]]ization [4]. The magnetization Ml perpendicular to the applied magnetic field B was measured by means of a cmtilever torque magnetome- tory. The torque is given by ? = M x E which is proportional to B2 for an anisotropic field-independent susceptibility x of the sample. In general, x is a tensor and the absolute value of the torque has th$ form r = AXB2sin229, where AZ is the susceptibility difference between two principal axes of the x tensor and r9is the angle between 1? and one of the prittcipal tensor axes. For a 2D Fermi surface the torque dHvA signal is proportional to dFhiQ, with F = FJCOSQand the angie~between B and the normal to the conducting planes. Fig. l(a) shows the torque signal at Q = -0.7" where the dHvA amplitude is very small and any nonlinearities of the torque signal can be excluded. The dHvA oscillations are sitting on a torque background which follows a B2 behavior up to the highest field. This background signal is up to T = 75 K almost temperature independent and shows a sin2fi dependence as expected for a static field-independent susceptibility (Fig. 2). One principal axis of the x tensor lies at @ = 30". The occurrence of this anisotropic susceptibility is rather unusual for the organic metals and the origin of the signa~in the present material is unclear. It might be a remnant of the local magnetism of the molecular bands.At low fields and high temperat...

Testing scuffing resistance of materials for marine 2-stroke engines – Difficulties with lab scale testing of a complex phenomenon

“…Such an effect could appear if lubricant additives are no longer present or cannot work properly. Also, the beneficial effect of sulphur in the fuel is commonly attributed to the propensity to build up a solid lubricating film [2,1]. Hence the solid lubrication could become worse due to a change of fuel and this would be especially critical when lubrication is impaired due to other reasons.…”

“…Results where scuffing is obtained even in the presence of lubricant have been published by other researchers. Ayaji et al [1] tested scuffing resistance with fully immersed contacts, but performed their tests in diesel fuel oils, which are not as lubricious as the fully formulated cylinder oil used in the present study. Scuffing tests have also been performed using polyalphaolefin (PAO) [16,7], and hexadecane [1].…”

“…Configurations include pin-on-twin (one cylinder reciprocating on two) [15], ball-on-flat (reciprocating and rotating) [1,16], cylinder-on-plate (pivoting) [17], pin-ondisc/block-on-ring (rotating) [18,7]. Most test procedures include an increase in the severity of the sliding contacts, for example by increase of speed [1], load [16,7] or by starved lubrication [18]. Some procedures do not include any increase in severity [15,17].…”

“…The beneficial tribological effect is attributed to sulphur in the fuel building up a solid lubricating film and promoting a beneficial mild corrosive wear. There are also experimental studies showing that fuel with lower sulphur content give a lower scuffing resistance [1,2]. The catastrophic nature of scuffing in engine cylinders implies a sudden shift from the normal low wear rate to a very high.…”

Near-frictionless carbon coatings for spark-ignited direct-injected fuel systems. Final report, January 2002.

“…42 The diesel-lubricated scuffing performance of NFC coatings was investigated by Ajayi et al, who found that coated surfaces would scuff only at contact stresses high enough to deform the substrate and delaminate the film, or after the NFC was removed by wear. 43 The scuffing performance of NFC in dry sliding conditions was then tested by Alzoubi et al 44 Again, NFC was found to provide an improvement in scuffing resistance of two orders of magnitude.…”