2-stroke low speed engine cylinder oil stress and shell ... · title: presentation title: futura...
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Copyright of Shell Global Solutions (Deutschland) GmbH
1 January 2012
2-Stroke Low Speed Engine Cylinder Oil Stress and Shell Alexia S4 development
CIMAC NMA Meeting
25th January 2012
Oslo, Norway
Luis García, Shell Global Solutions (Deutschland) GmbH
Copyright of Shell Global Solutions (Deutschland) GmbH
2 January 2012
The Oil Stress Concept
Shell developed the concept in 4-Stroke Medium Speed Engines (CIMAC Congress - 1998 & 2001)
An oil degrades in service as a result of its exposure to power.
Cumulative degrading processes of oil charge over service time (oil mean residence time).
Related to amount of power (and the way it is generated).
Oil Stress Factor (OSF)
Relation between:
Oil Consumption Rate, R [g/kWh]
Oil per kW of Power generated or Specific Sump Size, V [kg/kW]
Time of the oil in service, t [h]
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3 January 2012
The Oil Stress Concept Oil Stress Factor vs. Specific Oil Consumption
Oil Stress Factor vs. Oil Consumption in a 4-Stroke Medium Speed Diesel Engine
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0,00 0,20 0,40 0,60 0,80 1,00
OS
F [
kW
h/g
]
Oil Consumption R [g/kWh]
OSF kWh/g
Normal
Operation
Low Oil Consumption Shorter ODI
High Oil Consumption Longer ODI
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4 January 2012
Factors Influencing Oil Stress – CIMAC Paper, June 2010
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5 January 2012
Oil Stress in the 2-Stroke Low Speed Engine
Mini-sump -> thin oil film
Oil Film Thickness
Piston Rings Design
Loading and Speed
Liner Surface
Lubricant Viscosity
(Mean) Residence Time
Feed Rate (Effective Lube Refreshment Rate) -> g/kWh
Oil Film Thickness
Lubricant injection/distribution system (lube mass flow)
Evaporation or burned oil losses
Oil Film viewed as a “Mini Sump” for OSF calculations
Oil film thickness 1-8 µm Human hair
Copyright of Shell Global Solutions (Deutschland) GmbH
6 January 2012
Oil Stress in the 2-Stroke Low Speed Engine
Copyright © Wärtsilä Corporation Copyright © Wärtsilä Corporation
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7 January 2012
Oil Stress in the 2-Stroke Low Speed Engine
Acid Stress
Thermal Stress
Insolubles Stress
Humidity Stress
Oil Stress
R
D
B
G
“RS”
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8 January 2012
Oil Stress & Cylinder Lubricant Properties
Effect of fuel sulphur and air humidity on BN depletion
50%
60%
70%
80%
90%
100%
110%
0 5 10 15 20 25 30 35
BN
De
ple
tio
n [
%]
Absolute Scavenging Intake Air Humidity (g/m3)Dry Air Humid Air
1,7 % Sulphur
2,2 % Sulphur
2,7 % Sulphur
Copyright of Shell Global Solutions (Deutschland) GmbH
9 January 2012
Oil Stress & Cylinder Lubricant Properties Comparing samples
Higher OSF‟s lead to lubricant limits of desirable dispersancy performance.
Residual Total Base Number is not the only property describing oil performance. Lower quality spots correspond to those samples with higher residual TBN„s.
Heated Blotter Spots of “Ring Spray” oil samples from different configurations and ambient conditions
Humid Conditions OSF= 2,54 kWh/g
Cylinder A Dry Conditions OSF= 2,42 kWh/g
Cylinder B Dry Conditions OSF= 2,18 kWh/g
Humid Conditions OSF= 2,28 kWh/g
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10 January 2012
How Oil Stress – defines lubricant performance
Influence on performance + Low ++ Medium +++ High
Oil Stress Factor
Thermal Stress ++ + +++ +++
Insolubles Stress +++ ++ ++
Acid Stress +++ +
Humidity Stress ++ ++ + ++
Influence of Oil Stress Factor on Lubricant
Neutralisation
Capability
Cleanliness
Performance
Abrasive Wear
ProtectionThermostability
Viscosity
Control
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11 January 2012
Oil Performance Factors
Neutralisation Capability +++ ++ +Cleanliness (Detergency & Dispersancy) + +++ +++
Abrasive Wear Protection +++ +Thermostability ++ +++ +++Viscosity Control + ++ +++
Liner and
Piston Ring
Wear
Ring Land
and
Groove
Deposits
Engine
Cleanliness
Engine Performance Factors
How Oil Stress – defines lubrication performance
Relevance + Low ++ Medium +++ High
Copyright of Shell Global Solutions (Deutschland) GmbH
12 January 2012
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 20 40 60 80 100 120 140
Engi
ne L
oad
Residence Time in the Lubricating Film [seconds]
0,95 g/kWh
longer
Slow steaming
12
Factors Influencing Oil Stress Slow steaming conditions
Copyright of Shell Global Solutions (Deutschland) GmbH
13 January 2012
Summary Conclusions
Cylinder Oil “Ring spray” sampling combined with the quantification of ring spray oil loss increased understanding of the lubrication complexity in a 2-stroke engine.
Low engine load operation (Slow & “Flexible” Steaming) represent real challenges to existing cylinder lubricants
Understanding lubricant exposure is critical to designing new cylinder lubricants capable to withstand higher levels of Oil Stress – future cylinder lubricants must have a wider range of operational flexibility