Supercharging of internal combustion engines has been used for
many years as a method to improve engine performance and efficiency. Entering
the millennium, a new trend is appearing. The trend points to small displacement
engines in order to meet federal emission legislation on fuel consumption and
emission control. The driver, however, still demands the same performance they're
used to.
A good way to meet these needs is supercharging otherwise known
as forced induction. The purpose of supercharging an engine is to raise the
density of the air charge, before it's delivered to the cylinders. Thus, the
increased mass of air trapped and then compressed in each cylinder during each
induction and compression stroke makes more oxygen available for combustion
than the conventional method of drawing the fresh air charge into the cylinder
(naturally aspirated). Consequently, more air and fuel per cycle will be forced
into the cylinder, and this can be efficiently burnt during the combustion process
to raise the engine power output to higher than would otherwise be possible.
Generally, there are three basic types of "superchargers," the most
popular being the exhaust-gas driven turbocharger, mechanically driven superchargers
and the pressure-wave supercharger. The mechanically driven supercharger is
broken up into two groups as well, the mechanically driven centrifugal supercharger
and the mechanically-driven positive displacement supercharger such as the screw-type
and roots-type.
In automotive and marine applications, the pressure-wave supercharger is rarely
used. The turbo and roots-type superchargers have been the most popular forced
induction methods in the past. While the turbo creates great peak horsepower,
turbo lag and high cold start emissions due to the thermal mass are severe drawbacks
of the turbocharger. Small displacement engines need higher-pressure ratios
to achieve the performance demanded by the driver. This fact increases the mentioned
drawbacks of the turbo and makes the turbocharger a less desirable alternative
for supercharging than the mechanical twin-screw supercharger. The Whipple twin-screw
charger does not have the usual drawbacks of earlier mechanical superchargers
such as the roots-type, such as poor efficiency especially at high-pressure
ratios, high rpm, high noise level as well as high price. Comparative tests,
made independently by Whipple Industries, show that the twin-screw compressor
is the most effective supercharging method available.
Whipple Twin Screw
Operating Principles || Whipple
Twin Screw Supercharger
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