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
January 2012
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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 Oil
between:
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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January 2012
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The Oil Stress Concept Oil Stress Factor vs. Specific Oil Consumption Low Oil Consumption Shorter ODI
18,00
16,00
OSF kWh/g
14,00
OSF [kWh/g]
12,00
Normal
10,00
Operation
8,00
6,00
High Oil Consumption Longer ODI
4,00 2,00 0,00 0,00
0,20
0,40 0,60 Oil Consumption R [g/kWh]
0,80
1,00
Oil Stress Factor vs. Oil Consumption in a 4-Stroke Medium Speed Diesel Engine Copyright of Shell Global Solutions (Deutschland) GmbH
January 2012
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Factors Influencing Oil Stress – CIMAC Paper, June 2010
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January 2012
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Oil Stress in the 2-Stroke Low Speed Engine Mini-sump -> thin oil film Oil Film Thickness Piston Rings Design
Oil film thickness 1-8 µm
Human hair
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 Copyright of Shell Global Solutions (Deutschland) GmbH
Oil Film viewed as a “Mini Sump” for OSF calculations January 2012
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Oil Stress in the 2-Stroke Low Speed Engine
Copyright © Wärtsilä Corporation
Copyright of Shell Global Solutions (Deutschland) GmbH
Copyright © Wärtsilä Corporation
January 2012
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Oil Stress in the 2-Stroke Low Speed Engine G Humidity Stress
B
R
“RS ”
Thermal Stress
Oil Stress
Insolubles Stress
Acid Stress
D
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January 2012
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Oil Stress & Cylinder Lubricant Properties 110% 1,7 % Sulphur
100%
2,2 % Sulphur 2,7 % Sulphur
BN Depletion [%]
90% 80% 70% 60% 50% 0
5
10
15
20
25
30
35
Absolute Scavenging Intake Air Humidity (g/m3) Dry Air
Humid Air
Effect of fuel sulphur and air humidity on BN depletion Copyright of Shell Global Solutions (Deutschland) GmbH
January 2012
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Oil Stress & Cylinder Lubricant Properties Comparing samples Heated Blotter Spots of “Ring Spray” oil samples from different configurations and ambient conditions Cylinder A Dry Conditions OSF= 2,42 kWh/g
Humid Conditions OSF= 2,54 kWh/g
Cylinder B Dry Conditions OSF= 2,18 kWh/g
Humid Conditions OSF= 2,28 kWh/g
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.
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January 2012
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How Oil Stress – defines lubricant performance Influence of Oil Stress Factor on Lubricant
Neutralisation Capability
Cleanliness Performance
Abrasive Wear Thermostability Protection
Viscosity Control
Oil Stress Factor
Thermal Stress
++
+
Insolubles Stress
+++
++
Acid Stress
+++
Humidity Stress
++
Influence on performance Copyright of Shell Global Solutions (Deutschland) GmbH
+++
+++ ++
+ ++ + Low
+ ++ Medium
++
+++ High January 2012
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How Oil Stress – defines lubrication performance Engine Performance Factors
Liner and Piston Ring Wear
Ring Land and Groove Deposits
+++ + +++ ++ +
++ +++ + +++ ++
Engine Cleanliness
Oil Performance Factors Neutralisation Capability Cleanliness (Detergency & Dispersancy) Abrasive Wear Protection Thermostability Viscosity Control
Relevance Copyright of Shell Global Solutions (Deutschland) GmbH
+ Low
++ Medium
+ +++ +++ +++ +++ High
January 2012
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Factors Influencing Oil Stress Slow steaming conditions 0% 10% 20%
Engine Load
30%
Slow steaming
40%
50% 60% 70%
longer
80% 90% 100% 0
20
40
60
80
100
120
140
Residence Time in the Lubricating Film [seconds]
0,95 g/kWh Copyright of Shell Global Solutions (Deutschland) GmbH
January 2012
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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
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January 2012
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