Turbochargers and SuperchargersKarl Lynch

Increasing Engine Power• There are a few ways to increase

engine horsepower:▫ Larger engine displacement But it’s costly and adds unwanted

weight▫ Nitrous oxide Short duration of increased power

▫ Turbochargers and Superchargers Lightweight, relatively cheap,

continuous supply of powerTurbocharger

Brief History

• 1st forced induction patent in 1885 to Gottlieb Daimler

• 1st turbocharger patent given in 1905 to Alfred Büchi

• Installed on French WW1 fighter planes to limited success

• GE installed a turbocharger on a plane in 1918• Began being used on diesels in the 1920s

Forced Induction• All naturally aspirated engines use the down stroke of

the piston to create a low pressure area, drawing in the air and fuel mixture into the cylinder

• However, most engines cannot inhale the full displacement of the atmospheric-density fuel mixture▫ This volumetric efficiency varies from engine to engine

• Forced induction is when air is forced into the cylinder to increase the volumetric efficiency

How turbochargers work• They are used to increase the volumetric efficiency of the

engine by increasing the air-fuel mixture entering the cylinder

• The turbocharger housing contains a turbine and centrifugal air compressor on the same shaft

• The exhaust leaving cylinder spins turbine• The compressor forces more air into the cylinder▫ Compressor typically increases pressure by 6-8 psi,

but it can be greater• Increased air pressure allows more fuel to burn

• The compressed air is usually cooled to allow more air in the cylinder and to prevent knocking

• The increase of 6-8 psi increases horsepower by 30-40%

Turbocharger vs. Supercharger• Both operate on the same

principle▫ Both use forced induction to

increase engine performance• Supercharger use belts and

chains that are directly connected to the engine to drive the compressor▫ Results in the engine needing

to withstand the stresses of generating the increased power

Supercharger

• Turbochargers do not place a direct mechanical load on the engine▫ Allows the turbocharger to

produce more power that the supercharger without stronger hardware in the engine

Turbocharger connected to engine

• However, the increased power using a supercharger is immediate, while a turbocharger’s power increase contains a lag▫ The lag is because the turbine in the turbocharger

needs to increase in speed using the exhaust▫ Lag can be reduced by reducing the moment of inertia

of the turbine

Cut-away viewTurbine is on the left, compressor on the right

Applications• High altitudes:▫ Aircraft and automobiles▫ Air pressure is less at high

altitudes, so there is less air in naturally aspirated engines

▫ This leads to less power▫ Turbochargers will increase

the pressure, reducing altitude induced power loss

• Increasing power▫ Used on heavy trucks, ships,

etc.▫ Much better power:weight

ratio than just putting in a larger engine

Summary• Turbochargers are one of the best ways to increase power ▫ They’re lighter and cost less than a larger engine▫ Do not place as much stress on the engine as a supercharger does▫ They actually help to increase efficiency

Twin turbochargers on an engine