Superchargers

Axial inlet → compression → radial outlet.

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. The increased mass of air trapped and 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 engine power output higher than would otherwise be possible.

THREE BASIC TYPES OF SUPERCHARGER

EXHAUST-GAS DRIVEN

The turbocharger — the most popular type. Creates great peak horsepower, but turbo lag and high cold start emissions from thermal mass are severe drawbacks.
MECHANICALLY DRIVEN

Splits into centrifugal and positive displacement designs. Positive displacement covers both the screw-type and the roots-type compressor.
PRESSURE-WAVE

Rarely used in automotive and marine applications.

WHY THE TWIN SCREW WINS

Small displacement engines need higher pressure ratios to achieve the performance demanded by the driver. That fact increases the drawbacks of the turbo and makes it a less desirable alternative 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 — 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.