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4-stroke engine (4-cycle engine)This is an engine in which the pistons complete their power stroke every second crankshaft revolution. The four strokes are: intake, compression, power and exhaust. (also called: inlet, compression, combustion and outlet). The 4-stroke cycle is so called because it takes 4 strokes of the piston to complete the processes needed to convert the energy in the fuel into work. Because the engine is reciprocating, this means that the piston must move up and down the cylinder twice, and therefore the crankshaft must revolve twice.
• Low speed engine (Slow speed engine)An engine broadly defined as running at speeds below 300 rpm. Low speed engines are also called "slow speed" engines. Low speed engines are typically two stroke engines.
• Medium speed engineAn engine broadly defined as running at speeds of 300–1200 rpm.
• High speed engineAn engine broadly defined as running at speeds above 1200 rpm.
Remarks! These speed categories (low, medium, and high speed) are general "rules of thumb" and not officially defined by any regulatory body
The lubricant must remove sludge to prevent deposit formation
Sludge originates from:waterfuelsolid residues
Deposits and lacquercombustion products from fuelcombustion products from lubricantlubricant / fuel that has oxidisedlubricant / fuel that has crackedlubricant / fuel that has polymerised
Describes the amountof solid contaminantspresent in lube oilConsists of soot, dustand wear debris as wellas of oxidation productsderived from fuel /lube oilSeveral analysismethods exists havingan influence on exact analysed valueWärtsilä’s limit:
Describes the availablealkali reserve in lube oilBN is decreasing whenacid sulphur andnitrogen originatedcombustion residuesare reacting with alkalireserveSLOC and fuel S contentare the main factorsinfluencing on BNdepletion rateWärtsilä’s limit:
min. 20 mg KOH/gon HFO operationmax. 50% depletion on LFOoperation
Strong bonds between atoms within a layer and relatively weak interatomic interactions (van der Waals forces) between atoms ofdifferent layers allow the lamina to slide on one another
Graphitegraphite is structurally composed of planes of polycyclic C atoms that are hexagonal in orientation. The distance of carbon atoms between planes is longer and therefore the bonding is weakerwater vapour is a necessary component for graphite lubrication. The adsorption of water reduces the bonding energy between the hexagonal planes of the graphite to a lower level than the adhesion energy between a substrate and the graphite graphite is not effective in vacuum
MoS2the most widely used form of solid film lubrication todaylike graphite, it has a hexagonal crystal structure with the intrinsic property of easy shear: weak atomic interaction (Van der Waals) of the sulphide anions, while covalent bonds within molybdenum are strong lubrication relies on slippage along the sulphur atoms; all the properties of the lamella structure are intrinsic effective in vacuum or dry atmosphere the temperature limitation of MoS2 at 400ºC is restricted by oxidation.
WS2Max working temperatures about 100°C higher than MoS2
BN, “white graphite”Hexagonal Boron Nitride (h-BN, α-BN, or g-BN graphitic BN)high temperature resistance, 1200ºC service temperature in an oxidizing atmospherelubricant at both low and high temperatures (up to 900 °C, even in oxidizing atmosphere)since the lubricity mechanism does not involve water molecules trapped between the layers, boron nitride lubricants can be used even in vacuumhigh thermal conductivitythe cubic structure is very hard and used as an abrasive and cutting tool component
BaF2/CaF2
Ag
High Temperatures (effective lubricating above 400°C)
Thermal stability: very important since one of the most significant uses of these materials is in high temperature applications not tolerated by other lubricants:– Oxidation stability– High temperature corrosionVolatilityAdhesion on base materialHardnessThermal shock resistance…
SEM backscattered micrograph of a NiCr(80/20)/Cr2O3-Ag-BaF2·CaF2 coatingSource: W. Wang. Surface and Coatings