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ENGINE SUBSYSTEMS
LUBRICATION SUBSYSTEM:
Lubrication of moving parts is as crucial
for this engine as a reciprocating engine. However, even in the case
of lubrication subsystem failure the failure mode is gradually, with
the engine actually slowing down to a stop as the friction increases
rather than suddenly sizing as piston engines are inclined to
do.
The internal design does
require oil to be injected into the rotor chamber for lubrication.
In automotive use the engine draws on oil from the crankcase for
this purpose. A closer look at the system is available
here.
This is not a desirable feature
for hovercraft usage in that it can result in exhaustion of
lubricating oil in the crankcase, if not frequently checked, and the
carbon deposits from combustion of automobile engine oil causes
internal wear of the seals of the rotors.
Some alternatives to the above system are :
- Eliminate the crankcase oil injection
subsystem and instead mix 2 cycle oil in the gasoline. This has
proven to be a reliable method and removes the possibility of
crankcase oil exhaustion and improves the rotor seal life. It
does, however, require mixing the 2 cycle oil with each gasoline
fill up.
- Install a metering pump adapter, as
offered by PCV Technologies which takes the solution one step further in allowing to
still using the stock metering pump but supply it with two-stroke
oil.
Heat ejection by the
lubrication subsystem is crucial for maintaining engine temperature
within design limits. This is accomplished through an oil cooler
with a fin surface equal to that used in the automobile application.
Most aluminum oil cooler as used in race car applications will
provide this job.
Lubrication
Subsystem Instrumentation:
The
lubrication subsystem can be instrumented with an oil pressure
and oil temperature gauge mounted in the instrument
panel.
A dipstick provides for
oil quantity measurement.
ELECTRICAL/IGNITION
SUBSYSTEM:
Additional features relative to safety is that each rotor chamber
has two spark plugs with two independent ignition coils for each
plug set. There is one plug per rotor chamber referred to as the
"Lead" and one referred to as the "Trailing" plug. The trailing plug
in the automobile application is set to fire approximately 15
degrees after the lead plug fires. The engine will run on just the
trailing plug setting for auto application, however, there is
considerable power loss. While the trailing plug
was designed principally to meet auto emission and fuel economy
standards, it can be recalibrated to fire essentially in sync with
the lead plug providing true redundant ignition for the engine in
Hovercraft application. An after market ignition computer can
be used which provides two independent ignition CPUs and a
feature for checking each ignition coil subsystem
independently.
A in-depth file
regarding the electrical system of the Mazda rotary 13 B engine can
be found at : http://www.teamfc3s.org/info/articles/demystifying.html
The electric charging is accomplished with 12 volt marine
alternator ( single wire to high amp unit ) with internal voltage
regulator.
Electrical Subsystem
Instrumentation:
The electrical subsystem can
be instrumented with a High/Low voltage visual indicator as
well as a voltmeter which can be switched.
COOLING SUBSYSTEM:
Since the engine is liquid cooled the adverse effects
of "shock" cooling which can cause cylinder damage on air cooled
engines does not occur. Again, a positive feature. Due to the fact
that this small displacement engine does produce so much power
relative to its displacement, adequate cooling is a critical need to
remove the excess heat from the block. Approx. 1/3 of the heat
rejection (above that not ejected by the exhaust gases) is by the
lubrication system through an oil cooler. The remaining (approx. 2/3
of the waste heat) is ejected through a water based
coolant system using radiators
installed in the thrust duct exit section of the craft or any
location where adequate airflow is possible.
Additionally, since the engine is liquid
cooled, cabin heat can be derived from an heat exchanger in
the cockpit to transfer heat from the coolant system into the
cockpit. The heat exchanger can have a manual coolant cutoff
valve as well as a manually controlled fan. This approach removes
the danger of carbon monoxide leaking into the cabin through the
typical exhaust muff approach to heating .
Coolant Subsystem
Instrumentation:
The coolant
system can be instrumented with both a coolant temperature
gage and a coolant pressure gage.
The coolant pressure gage will immediately indicate
any abnormality and provide early warning of a leak giving time for
a flight to be terminated before complete loss of
coolant.
If only a coolant
temperature gage were used, considerable loss of coolant is possible
before a rise in temperature would indicate a problem existed.
Therefore, the coolant pressure gage is considered a crucial feature
of any liquid coolant system in an Hovercraft.
PROPELLER SPEED REDUCTION UNIT
(PSRU):
A PSRU is used to reduce the engine RPM to that required for
efficient and safe propeller / fan operation.
The PSRU is
provided by "GoodYear" orange eagle PD belts ( w=700mm)in a ratio
2:1 .
Alternative a Ross Aero PSRU designed for the
Mazda 13B using planetary gears providing a 2.17:1 reduction.
FUEL SUBSYSTEM:
The fuel
subsystem in our case is adjusted to a carburated engine. It consist
of a marine fuel pump, inlet filter, outlet filter and fuel pressure
regulator with return line. All fuel lines consist of USCG
compliant hoses. The fuel system was pressurized with
air to test for leaks.
For a more detailed file please see
: fuel system
on high speed Hovercraft
SUMMARY
In summary, I believe the engine has a number of inherently
desirable features and benefits for hovercraft use. The
adaptations to make it suitable for hovercraft use have been
carefully thought out and failure modes thoroughly examined.
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