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My
new boat has a single turbocharged diesel. Can you give me a primer on
how it works and the maintenance involved? C.R., via e-mail
A
turbocharger is a mechanically simple device composed of two sealed chambers
containing fan blades—also known as turbines—connected by
a shaft. Exhaust passes through the first chamber, which is made of cast
iron and is also called the “hot side,” spinning the turbine.
This causes the turbine on the “cold side,” which is made
of aluminum, to spin, drawing in outside air and forcing it into a passage
called the volute, which gradually decreases in size and terminates at
the intake manifold. The greater the load on the engine, the higher the
volume of exhaust and thus the more fresh air—and by extension,
fuel—that is pumped into the engine, increasing output. For this
reason, a turbocharger is said to be “load-sensitive,” as
opposed to a mechanical supercharger that provides additional horsepower
according only to engine speed. When enough air is pumped into the cylinders
that the pressure there exceeds atmospheric pressure, the turbocharger
is said to generate “boost,” which is measured in pounds per
square inch (psi) in nonmetric countries. In countries using the metric
system, it’s measured in atmospheres, or bars; 1 atmosphere equals
13.7 psi.
The
area between the hot and cold sides contains bearings, on which runs the
shaft that connects the compressor and exhaust turbines. As the shaft
can spin at speeds in excess of 100,000 rpm and temperatures here can
top 800°F, right oil flow is critical for both cooling and lubrication.
Use the proper oil—CC- or CD-rated—and change it and all filters
at or before the recommended interval. Periodically inspect the area between
the two chambers for signs of leakage. If the seals here fail, so will
the bearing and, ultimately, the turbocharger. Occasionally visually inspect
both turbines for signs of damage or excessive deposits. The hot-side
turbine will normally be coated with black soot. Finally, let your engine
cool down for two to three minutes at idle before shutting it down.
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