Download - Royal Australian Navy

14 NAVY ENGINEERING BULLETIN MARCH 2003
GT Selection
19. The gas turbine selection,
though preliminary, was made
considering all gas turbine
manufacturers available at the
time of research. Each
representative for the
manufacturer was asked to
supply information that could
meet the following requirements:
a. Produce 3600kW or be able
to be electronically limited to
3600kW;
b. Have an output shaft speed of
between 300 and 1200rpm;
c. Able to fit with the same
dimensions as the PDEs;
d. No increase in the hull noise
signature;
e. Be able to run on F76 and
F44 fuel; and
f. Able to integrate easily with
the C&M System.
20. The LM500’s performance,
fuel consumption characteristics,
easily integrated control and
monitoring method, cost and
commonality of parts with the
LM2500 meant that the LM500
was selected, thus enabling a
physical review of the proposal.
Modification Considerations
21. PDE Removal: The first step in
the modification is the removal of
the PDE, which already has a
designated removal route, and
redundant systems. The
redundant systems to be
removed include; Seawater
system, PDE Enclosure, Control
air, Lube oil circulation tanks,
Lube oil replenishment system,
Coolant recirculation system,
PDE’s Local Operating Panel
(LOP), and Drainage and dirty oil
system.
22. Stability: The modification
shall require the importing of
approximately 11,000kg and
export of 60,100kg. This fifty
tonne difference does affect the
ship’s stability by causing the
centre of gravity to increase from
6m to 6.08m. Thus, would have
little effect on the ship’s
operation unless severe flooding
was experienced.
23. Power transfer: The LM500
has an output of 4.4MW and a
maximum operating shaft speed
of 7000RPM. However, it has an
incorporated gearbox that
reduces the output shaft speed to
that of the PDEs (300 –
1200RPM), enabling the LM500
to be connected directly to the
existing Geislinger Coupling.
24. Intake and Exhaust: The
LM500 has a greater air flow
rate, but lower exhaust temp,
than that of the PDEs.
Calculations have shown existing
intake plenums and exhaust
trunkings are sufficient. 5
25. Control and Monitoring: This
may seem to be one of the more
complex obstacles in the
modification, however it is
relatively simple. The C&M
Siemens display changes are a
matter of simple programming
changes, whilst the monitoring
system changes will require
connection of the LM500 ECM to
the existing C&M wiring. The
program will then have to be
changed to ensure that the
displays and control are corrected
for the input/output voltages.
However the engine power
requirements are different, as the
LM500 sets a PLA (not RPM as
for the PDEs), and will therefore
require trials to set PLA for shaft
RPM.
Integration Issues
26. Some of the perceived
integration issues that could
occur with the change include; an
increased IR signature, and fuel
consumption at lower speeds.
Whilst gas turbines are renowned
for a large heat plume during
operation, this can be reduced by
using a venturi effect to draw in
ambient air. It could be safely
predicted that the exhaust
experienced after the
modification will most likely not
require any further reduction in IR
signature, with the air-diluting
duct already fitted to the ANZAC
Class ships.
27. However a major flaw with the
LM500 (or any gas turbine) is low
load, or idle, fuel consumption
compared with a diesel. As
shown in the earlier figure.
Conclusion
28. The proposal has clear
benefits with operations,
maintenance, reliability, support
requirements, environmental
issues and costs. Whilst the
change to LM500s is a feasible
project, both financially and
practically, it is never likely to
eventuate. The article was
forwarded to inspire technical
discussion, and encourage others
to utilise their engineering
prowess to see that some
solutions are outside the square.
Notes
1 Major parts are classified as items that
are constantly cycling to keep the engine
self-sustaining, such as rockers, shafts,
pushrods, etc, but not dividing into their
components or considering fuel racks, or
variable stator vanes.
2 The cost analysis utilises information
from PDE experience, and records obtained
from serving ANZACs (AMPS). It also drew
upon documentation and records supplied
from GE regarding the LM500’s marine
propulsion service, combined with current
RAN gas turbine operating experience.
3 Even though each ship should not expect
a prime mover to fail, one total failure for
both the LM500 and PDE, requiring
overhaul, was assumed to occur once in
the life of the ship, and included in the
cost analysis. This was done to enable an
even comparison, noting that one PDE has
already failed on HMAS ANZAC.
4 Calculations were completed with
assistance from project managers, both
RAN and private industry. The end
production figure was then given a 25%
increase for expansion of work, and
rounded up to the nearest million dollars.
5 Calculations conducted by Author, iaw
theories and formulas from Marks’
Standard Handbook For Mechanical
Engineers (Tenth Edition), McGraw Hill.