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11. SELECTING FUELS
FOR STANDBY
DEPENDABILITY
The types of fuels available for diesel engines, vary
from highly volatile jet fuels and kerosene to the
heavier fuel oils. Most diesel engines are capable
of burning a wide range of fuels within these
extremes. The following information will assist you
in selecting the type of fuel that will afford the best
overall performance and reliability of your
Generating Set.
11.1 Types Of Fuel Oil
The quality of fuel oil can be a dominant factor in
satisfactory engine life and performance. A large
variety of fuel oils are marketed for diesel engine
use. Their properties depend upon the refining
practices employed and the nature of the crude oils
from which they are produced. For example, fuel
oils may be produced within the boiling range of
148 to 371
°
C (300 to 700°F), having many possible
combinations of other properties.
The additional contaminants present in low grade
fuels may result in darker exhaust and more
pronounced odour. This may be objectionable in
hospitals, offices commercial and urban locations.
Thus, location, application and environmental
conditions should be considered when selecting
fuel.
The Generating Set owner may elect to use a low
grade fuel because high-grade fuels are not readily
available in his area or because he can realise a net
saving with low grade fuels despite higher engine
maintenance costs. In that case, frequent
examination of lubrication oil should be made to
determine sludge formation and the extent of lube
oil contamination.
Aside from the various grades of fuel oil commonly
used in diesel engines, aircraft jet fuels also are
sometimes used, especially in circumstances where
the jet fuels are more readily available than
conventional fuels. Jet fuels are lower in B.T.U.
content and lubrication quality than conventional
fuels. As a result, some diesel fuel systems must
undergo major modifications to accommodate this
type of fuel. For use of jet fuel please consult FG
Wilson.
Reliable operation of diesel engines may vary from
one fuel to another, depending on many factors,
including fuel characteristics and engine operating
conditions.
The fuels commonly known as high-grade fuels
seldom contribute to the formation of harmful
engine deposits and corrosion. On the other hand,
while refining improves the fuel, it also lowers the
B.T.U. or heat value of the fuel. As a result, the
higher grade fuels develop slightly less power than
the same quantity of low grade fuel. This is
usually more than offset by the advantages of high
grade fuels such as quicker starts and less frequent
overhauls. Before using low-grade fuels, therefore,
some understanding of the problems and extra
costs that may be encountered is necessary.
Fuels with high sulphur content cause corrosion,
wear and deposits in the engine. Fuels that are not
volatile enough or don't ignite rapidly may leave
harmful deposits in the engine and may cause poor
starting or running under adverse operating
conditions. The use of low grade fuels may require
the use of high priced, higher detergent lubricating
oils and more frequent oil changes.
11.2 Fuel Selection Guide
Specify fuel properties according to the following
chart.
Final
Boiling
Point
Cetane
Number
(Min)
Sulphur
Number
(Max)
Winter
290
°
C (550ºF)
45
0.5 %
Summer
315
°
C (600ºF)
40
0.5 %
Selecting a fuel that keeps within these
specifications will tend to reduce the possibility of
harmful deposits and corrosion in the engine, both
of which could result in more frequent overhauls
and greater maintenance expense. Specify exact
fuel properties to your local fuel supplier.
11.3 Maintaining Fresh Fuel
Most fuels deteriorate if they stand unused for a
period of many months. With standby generators it
is preferable to store only enough fuel to support a
few days or even only eight hours of continuous
running of the Generating Set so that normal engine
testing will turn over a tank full within a year and a
half.
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