Supercharger

Supercharging is less commonly used in the 21st century, as manufacturers have shifted to turbochargers to reduce fuel consumption and increase power outputs.

Roots blowers (a positive displacement design) tend to be only 40–50% efficient at high boost levels, compared with 70-85% for dynamic superchargers.

Positive displacement pumps deliver a nearly fixed volume of air per revolution of the compressor (except for leakage, which typically has a reduced effect at higher engine speeds).

Dynamic compressors rely on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down.

Major types of a dynamic compressor are: Common methods of driving a supercharger include: Fuels with a higher octane rating are better able to resist autoignition and detonation.

Using such fuels, aero engines like the Rolls-Royce Merlin 66 and Daimler-Benz DB 605 DC produced power outputs of up to 2,000 hp (1,500 kW).

For this reason, supercharged engines are common in applications where throttle response is a key concern, such as drag racing and tractor pulling competitions.

The majority of aircraft engines used during World War II used mechanically driven superchargers because they had some significant manufacturing advantages over turbochargers.

Such damage was a prominent problem in the early models of the American Boeing B-29 Superfortress high-altitude bombers used in the Pacific Theater of Operations during 1944–45.

Turbocharged piston engines continued to be used in a large number of postwar airplanes, such as the B-50 Superfortress, the KC-97 Stratofreighter, the Boeing 377 Stratocruiser, the Lockheed Constellation, and the C-124 Globemaster II.

The design used a complex series of bypass valves in the induction and exhaust systems as well as an electromagnetic clutch so that, at low engine speeds, a boost was derived from the supercharger.

In turn, this approach brought greater complexity and affected the car's reliability in WRC events, as well as increasing the weight of engine ancillaries in the finished design.

In 1935, the development of screw-type superchargers reached a milestone when Swedish engineer Alf Lysholm patented a design for a rotary-screw compressor with five female and four male rotors.

[15] In the 21st century, supercharged production car engines have become less common, as manufacturers have shifted to turbocharging to achieve higher fuel economy and power outputs.

The gears connected the supercharger to the engine using a system of hydraulic clutches, which were initially manually engaged or disengaged by the pilot with a control in the cockpit.

In the Battle of Britain the Spitfire and Hurricane planes powered by the Rolls-Royce Merlin engine were equipped largely with single-stage and single-speed superchargers.

This can largely be attributed to the higher temperature and lighter alloys that make turbochargers more efficient than superchargers, as well as the lower maintenance due to less moving parts.

For example, the air density at 30,000 ft (9,100 m) is 1⁄3 of that at sea level, resulting in 1⁄3 as much fuel being able to be burnt in a naturally aspirated engine, therefore the power output would be greatly reduced.

As the aircraft climbs and the air density drops, the throttle can be progressively opened to obtain the maximum safe power level for a given altitude.

Above the critical altitude, engine power output will reduce as the supercharger can no longer fully compensate for the decreasing air density.