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 TM 5-685/NAVFAC MO-912
but the coolant should be allowed to circulate
through the supercharger.
(4) Operating instructions. Manufacturer's in-
structions must be followed to ensure proper opera-
tion of superchargers. Filtered air only should enter
the air inlet, because foreign matter can cause rotor
imbalance and damaging vibration. The manufac-
turer's recommendations for lubrication must be fol-
lowed. Proper lubrication is necessary because the
unit operates at high speed and at high tempera-
ture. Not more than 15 seconds should elapse be-
tween the start of rotation and an oil pressure indi-
cation of 12 to 71 psi. Coolant circulation through
the turbocharger should be regulated so the tem-
perature rise does not exceed 30" Fahrenheit at full
engine load. A rise in excess of 30" Fahrenheit indi-
cates faulty circulation. Coolant should be allowed
to circulate through the turbocharger for about 5
minutes after the engine is shutdown.
b. Aspiration. The term "naturally-aspirated" is
applied to engines that are not supercharged. A four
stroke cycle engine performs its own air pumping
action with the piston intake stroke. When it is
supercharged, a four-stroke engine with a blower or
turbocharger provides pressure in the intake mani-
fold greater than atmospheric. The increased pres-
Figure 3-15. Oil bath air cleaner:
sure in the intake manifold is referred to as "boost".
Two stroke cycle engines require an air supply un-
(2) Methods. The most successful method of su-
der pressure to provide scavenging air.
percharging is the use of a turbocharger driven by
3-10. Exhaust system.
exhaust gas (see fig 3-16). The heat and energy
pulsations in the exhaust gas, which are usually
Components. The exhaust system consists of the
lost in the exhaust silencer, are used to drive a
engine exhaust manifold and includes piping, ex-
single-stage centrifugal turbine. The exhaust gas
pansion joints, silencers, and exhaust pipe. Also the
turbine is coupled to a centrifugal compressor that
system may include exhaust waste heat recovery
compresses the air to a pressure of four or five
equipment. The purpose of the system is to remove
psi. The engine's pressurized air is then delivered to
exhaust gas from engine cylinders to the atmo-
the individual cylinders through the intake mani-
sphere. Parts of the system are shown in figure 3-6.
fold.
(3) Disadvantages. Although the supercharged
to protect personnel from asphyxiation, and equip-
engine has many advantages over nonsupercharged
ment from fire and explosion. Exhaust from gaso-
line engines can contain dangerous carbon monox-
engines, its disadvantages are not insignificant. The
ide. Diesel engine exhaust includes objectionable
turbocharger is another piece of equipment to main-
smoke and odors. On supercharged engines, leaks
tain and operate. It operates at varying speeds de-
ahead of the turbine cause a loss of power.
pending on engine load, barometric pressure, inlet
(b) Piping. Exhaust piping must be the correct
air temperature, exhaust temperature, smoke con-
size to minimize exhaust back pressure. Connec-
tent of the exhaust, or accumulations of dust and
tions between exhaust manifold and piping should
dirt on the impeller and diffuser. It may operate at
have an expansion joint and the exhaust pipes
very high speed (up to 120,000 rpm) with a full load
should slope away from the engine. Also the exhaust
on the engine and thus be subjected to all the
pipes should have suitable devices to prevent entry
troubles of high-speed equipment. With proper
of rainwater. The length of tail pipes from silencer
maintenance, however, the turbocharger can be op-
to atmosphere should be kept to a minimum.
erated very successfully. If the turbocharger fails,
(c) Silencers. Silencers are used to reduce or
the engine can usually be operated at reduced load
muffle engine exhaust noise. Silencing engine ex-
as a nonsupercharged engine. The turbocharger can
haust sounds consists of trapping and breaking up
be partially dissembled and the opening blocked off,
3-21
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