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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
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