Lubrication in Four-Stroke Marine Diesel Engines E. Hlede L.Davia
Attrito, Usura e Lubrificazione in Campo Navale Napoli, 13 Maggio 2010 XI Convegno di Tribologia
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Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
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Table of contents
• Introduction to Wärtsilä • Introduction to 4-stroke Diesel engines • Diesel Engine Lubrication • Future Prospectives
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This is Wärtsilä
SHIP POWER
POWER PLANTS
SERVICES
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Wärtsilä Ship Power
Merchant
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Offshore
Cruise and Ferry
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Navy
Special Vessels
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• Flexible Baseload Power Generation for the developing world, islands, remote areas • Grid Stability and Peaking for strong grids, enabling increase of renewables • Industrial Self-Generation for large industries • For the Oil and Gas Industry mechanical drives and field power
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Wärtsilä Services
WE SUPPORT OUR CUSTOMERS THROUGHOUT THE LIFE-CYCLE OF THEIR INSTALLATIONS BY OPTIMISING EFFICIENCY AND PERFORMANCE
We provide the broadest portfolio and best services in the industry for both ship power and power plants. We offer expertise, proximity and responsiveness for all customers regardless of their equipment make in the most environmentally sound way.
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Wärtsilä Italia Engines
from
To
1,860
7,200
kW
W38B
4,350 11,600
kW
W46
5,850 20,790
kW
W46F
7,500 20,000
kW
W50DF
5,500 17,100
kW
W64 12,060 17,200
kW
W26
W26
W46F
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W38
W46
50DF
Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
W64
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Wärtsilä R&D footprint Trondheim, Norway Frequency converters
Stord, Norway Electrical & Automation systems
Vaasa, Finland W20; W32/32DF/34SG, Ecotech
Turku, Finland
Rubbestadneset, Norway
Ecotech
Espoo, Finland
CPP, Gears
Fuel cells, Ecotech
Drunen, The Netherlands CPP, FPP, Thrusters
Havant, UK; Slough, UK
Winterthur, Switzerland
Face Seals, Synthetic Bearings
2-stroke: RT-flex, RTA
Trieste, Italy
Toyama, Japan
W26, W38, W46, W46F, W50DF, W64
Rubber Seals & Bearings
Bermeo, Spain W34SG, W50DF
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Introduction to 4-stroke Diesel engines
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.
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Introduction to 4-stroke Diesel engines Diesel engine operating principle (4-stroke)
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Introduction to 4-stroke Diesel engines Division of engines according to speed
• 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 engine An engine broadly defined as running at speeds of 300–1200 rpm. • High speed engine An 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
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Diesel Engine Lubrication
Function of lubricating oil Lubricating oil is an integrated engine component Main function of lubricating oil is to maintain power producing efficiency and ability by
lubrication and sealing cooling cleanliness corrosion protection
while staying in good condition
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Influence of lubricating oil properties on engine components Fuel injection pump: Fuel / lubricating oil compatibility
Piston cooling gallery, ring groove area, Piston skirt, cylinder liner: High temperature detergency Thermal stability Alkalinity Antiwear Oxidation stability Cams and rollers: Antiwear Extreme pressure
Separator
”Cold” engine components: Low temperature detergency Corrosion resistance Cooler
Pump
Filter
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Bearings: Corrosion resistance Oxidation stability
Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
Crankcase: Water resistance Foaming resistance Dispersancy Detergency
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Function of lubricating oil
Lubrication and sealing Cooling Cleanliness Corrosion protection
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Function of lubricating oil
Lubrication and sealing Cooling Cleanliness Corrosion protection
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Types of lubrication Load
Load
Movement Bearing
Oil out
Oil out Oil in
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Hydrodynamic lubrication
Hydrostatic lubrication
Boundary lubrication
Metal to metal contact
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Properties related to lubrication
Viscosity: 170
160
150
140
130
120 0
1000
2000
3000
4000
OIL SERVICE HOURS (h) VISCOSITY AT 40 °C
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VISCOSITY AT 100 °C
Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
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Measure of fluid’s resistance to flow Viscosity increase indicates: oil oxidation presence of soot & combustion originated material HFO leakage to lube oil Viscosity decrease indicates LFO leakage to lube oil Wärtsilä’s limit: -20% / +25% 5000 change @ 100 °C -25% / +45% change @ 40 °C
Function of lubricating oil
Lubrication and sealing Cooling Cleanliness Corrosion protection
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Cooling of engine components
Bearings Pistons
Example of average oil temperature in piston 120
TEMPERATURE (°C)
110 OIL TEMP ERATURE OUT OF PISTON 100
90
80 OIL TEMP ERATURE INTO PISTON 70 0
25
50
75
100
125
ENGINE LOAD (% )
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Function of lubricating oil
Lubrication and sealing Cooling Cleanliness Corrosion protection
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Engine cleanliness
The lubricant must remove sludge to prevent deposit formation Sludge originates from: water fuel solid residues Deposits and lacquer combustion products from fuel combustion products from lubricant lubricant / fuel that has oxidised lubricant / fuel that has cracked lubricant / fuel that has polymerised Fuel / lubricating oil compatibility is important
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Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
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Piston cooling gallery cleanliness Influence of piston cooling gallery deposit thickness on piston top temperature 250
Limits: W32, 38, 46, 64 - aver. 300 μm - max. 400 μm W20, W26 - aver. 200 μm - max. 300 μm
200
150
100
50
0 0
200
400
600
800
DEPOSIT THICKNESS [ μ m]
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1000
Properties related to cleanliness
Insolubles:
1.0
0.8
0.6
0.4
0.2
0.0 0
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1000
2000 3000 OIL SERVICE HOURS (h)
Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
4000
Describes the amount of solid contaminants present in lube oil Consists of soot, dust and wear debris as well as of oxidation products derived from fuel / lube oil Several analysis methods exists having an influence on exact analysed value Wärtsilä’s limit: max. 2.0 % m/m measured with 5000 ASTM D 893b method
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Function of lubricating oil
Lubrication and sealing Cooling Cleanliness Corrosion protection
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Properties related to corrosion protection
Base Number (BN): 55
50
45
40
35
30
25
20 0
1000
2000
3000
OIL SERVICE HOURS (h)
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Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
4000
Describes the available alkali reserve in lube oil BN is decreasing when acid sulphur and nitrogen originated combustion residues are reacting with alkali reserve SLOC and fuel S content are the main factors influencing on BN depletion rate Wärtsilä’s limit: min. 20 mg KOH/g on HFO operation max. 50% 5000 depletion on LFO operation
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Wear, mm/10000 h
Example of wear rates
Corrosive wear increases at higher fuel sulphur levels
Corrosive wear decreases dramatically at higher BN
High sulphur fuel
Low sulphur fuel
0
5
10
15
20
25
30
BN, mg KOH/g
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Reasons for oil change, HFO operation 100
80
75
75
60
40
20
20
20 5
5
0 Viscosity
Insolubles 1
Other
Without anti-polishing ring
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Base Number Viscosity 2 With anti-polishing ring
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Other
Base number depletion
Fuel sulphur No antipolishing ring Dry sump
Base number (mg KOH/g)
40
S = 1.75 % m/m SLOC = 1.2 g/kWh LV = 1.5 l/kW
30 S = 3.5 % m/m SLOC = 1.2 g/kWh LV = 1.5 l/kW
Condemning limit
20
S = 3.5 % m/m SLOC = 0.4 g/kWh LV = 1.5 l/kW
Change interval
10 S = 3.5 % m/m SLOC = 0.4 g/kWh LV = 0.75 l/kW
0
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1000
2000
3000
4000 5000 6000 Running hours (h)
Lubrication in 4-Stroke Marine Diesel Engines / E Hlede - L Davia
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7000
8000
9000
10000
Properties related to wear
Iron (Fe):
50
Indicates mainly wear of cylinder liners and pistons Fresh oil can contain iron up to 10 ppm originating from tanks and pipes Typical analysis accuracy ±10%
40
30
20
10
0 0
1000
2000
3000
4000
OIL SERVICE HOURS (h)
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5000
Summary of main lube oil characteristics IMPACT ON ENGINE OPERATION
CONDEMNING LIMIT (HFO OPERATION)
Low base number
Corrosive wear Liner, piston ring groove
min. 20 mg KOH/g
Insolubles
High insolubles content
Dirty engine Deposit formation Wear of bearings etc.
max. 2.0 % m/m in n-pentane
Viscosity
High viscosity
More friction Reduced cooling
45% increase at 40 °C 25% increase at 100 °C
Low viscosity
Thinner oil film Metal - metal contact
25% decrease at 40 °C 20% decrease at 100 °C
High water content
Deterioration of oil film Bearing damage
PROPERTY
CHANGE IN PROPERTY
Base number
Water content
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max. 0.3 % V/V
FUTURE PROSPECTS IN ENGINE LUBRICATION
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Engine energy losses
About 10-15% of all energy supplied to an engine is lost due to friction
Other 20%
Crank train 15% Valve train 5%
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Piston assembly 60%
Solid lubricants
Low friction coefficient (≤ 0.4) Lattice structure arranged in layers Strong bonds between atoms within a layer and relatively weak interatomic interactions (van der Waals forces) between atoms of different layers allow the lamina to slide on one another
Low shear strenght
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Solid lubricants 9 Graphite
graphite 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 weaker
water 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 Æ graphite is not effective in vacuum
Graphite structure 34
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Solid lubricants 9 MoS2
the most widely used form of solid film lubrication today like 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 Æ effective in vacuum or dry atmosphere the temperature limitation of MoS2 at 400ºC is restricted by oxidation.
MoS2 structure S Mo S S Mo S
9 WS2
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Max working temperatures about 100°C higher than MoS2
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Solid lubricants
9 BN, “white graphite”
Hexagonal Boron Nitride (h-BN, α-BN, or g-BN graphitic BN) high temperature resistance, 1200ºC service temperature in an oxidizing atmosphere lubricant 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 vacuum high thermal conductivity the cubic structure is very hard and used as an abrasive and cutting tool component
9 BaF2/CaF2
High Temperatures (effective lubricating above 400°C)
9 Ag
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Self-lubricating coatings
9 Thin coatings Physical Vapor Deposition (PVD) , Chemical Vapor Deposition (CVD), … Thickness ≤ 10 μm
9 Thick coatings Air or Vacuum Plasma Spray (APS and VPS), High-velocity Oxy-fuel Spray (HVOF), Plasma Transferred Arc (PTA), ... Cermets coatings 0,1 mm ≤ thickness ≤ 15 mm
High-velocity oxyfuel process 37
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Self-lubricating coatings Properties & Selection: 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 corrosion Volatility Adhesion on base material Hardness Thermal shock resistance …
SEM backscattered micrograph of a NiCr(80/20)/Cr2O3-Ag-BaF2·CaF2 coating Source: W. Wang. Surface and Coatings Technology 177 –178 (2004) 12–17 38
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Benefits in engine components Functional coated components enabling: Use of new clean fuels (ultra low sulphur) and other new fuels (bio fuels etc.) Use of different fuels in multi-fuel engines Improve durability (especially for components running at high temperature) Better performance (↓NOx and ↓CO2) Reduce oil dependence Green products
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