Spectrographic measurements of the luboil determine its metal
composition. The presence of certain elements can uniquely identify
additives and contaminants in the luboil, the type of any contamination
and the condition of machinery.
For example, Aluminium is a general indicator of wear from
Aluminium piston skirts, with a typical value below 10 ppm.
Levels may rise if a piston has been replaced in an engine.
In an engine oil it may indicate the presence of catalytic
fines present in the fuel oil.
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source" guide, email us at
The
significance of Viscosity Index (VI)
For luboils, oil viscosity decreases as temperature increases.
Lubricants subjected to a wide range of operating and ambient
temperatures require a lubricant that exhibits minimum relative
change on its viscosity with broad variations in temperature.
For luboils with similar kinematic viscosity, the higher the
VI, the smaller the effect of temperature on its viscosity.
To better understand VI, we need to review how it was developed
many years ago:
VI is a means of classifying the viscosity vs. temperature
behaviour of luboils, on the basis of two reference luboils
selected to represent two extremes of behaviour:
The reference oil for high (H) VI was assigned a VI of
100. The oil used was a paraffinic base oil from Pennsylvania
crude oil, which many years ago were considered to display
the best viscosity vs. temperature characteristics.
The reference oil for Low (L) VI was assigned a VI of
0 and was a naphthenic base oil from the coastal region
of Gulf of Mexico, which showed a very poor viscosity vs.
temperature relationship.
Using this simple approach, lubricants that exhibit less
change in viscosity (with respect to temperature) than the
reference oil H, will have a VI greater than 100. Most synthetic
oils would be in that category. Lubricants having viscosity
change (with respect to temperature) greater than the reference
oil L, will have a negative VI.
In terms of lubrication, the most important property to ensure
optimum oil film strength (at the point of contact between
the two metal surfaces) is the actual viscosity of the luboil.
As temperature increases, a synthetic luboil would be more
viscous, better able to maintain oil film thickness and thus
more able to (relatively) reduce component wear. Hot running
systems such as Compressors, gearboxes and turbochargers,
are likely to benefit from such high VI synthetic luboils.
As temperature decreases below zero, a mineral luboil would
become too viscous, to the point where it cannot be pumped
or flow to the area requiring lubrication. This would result
in poor lubrication or even system starvation of sufficient
luboil to prevent metal-to-metal contact, which would lead
to increased wear. Critical deck equipment operating under
extremely low temperatures or wide temperature variations,
would benefit from the wider operating temperature range of
synthetic luboils.
Hints
and Tips
Before filling grease into a new grease gun, consider disassembling
the gun and cleaning it thoroughly, as it is likely that metal
shavings may be found in new grease guns. The metal shavings
may be present from the manufacturing process of the grease
gun.
A
better balanced engine saves fuel
Cylinder pressure is the most important parameter for describing
the operating condition of a diesel engine. There are many diagnostic
tools that optimise the performance of diesel engines, from
mechanical to portable electronic ones and to continuous online
monitoring of cylinder pressure readily integrated into the
ship's overall automation system.
Late or retarded fuel injection, can account for up to 2%
of fuel wastage per degree of late injection.
Owners can reduce their fuel oil bill, by considering the
following factors :
More efficient timing combustion
More efficient cooling
Optimising blended ratio performance
Engines that are timed according to OEM engine manual or
testbed data use theoretical settings, which may not correspond
to the ideal injection setting of the engine in service. It
is also likely that the timing tolerances would vary, as the
engine experiences normal wear and tear while in service.
Precise information enabling the engineer to regularly adjust
the fuel system to optimise cylinder performance, would be
an important contributor to reducing the fuel oil bill.
In addition, accurate measurements of cylinder pressure and
subsequent trend analysis will indicate early warning signals
of deteriorating cylinder performance. Such trend analysis
will help identify onset of wear in piston rings, fuel injectors,
exhaust valves, fuel pumps, etc.
A portable pressure meter that can help engineers reduce
costs, by adjusting engine tuning to the lowest fuel consumption,
and getting early warning of faults and onset of wear, may
be of use to you. To receive further product details and examples
of comparing a whole set of engine cylinders, and graphical
analysis of CP and PV diagrams, email us at
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