39 Questions
How does a variable-geometry turbocharger maintain optimum aspect ratio at different engine speeds?
By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. This allows for reduced lag, a lower boost threshold, and greater efficiency at higher engine speeds.
What is the purpose of an electrically-assisted turbocharger?
An electrically-assisted turbocharger combines a traditional exhaust-powered turbine with an electric motor to reduce turbo lag.
What is the function of the compressor in a turbocharger system?
The compressor draws in outside air through the engine's intake system, pressurises it, then feeds it into the combustion chambers (via the inlet manifold).
What is the role of the center hub rotating assembly (CHRA) in a turbocharger?
The center hub rotating assembly (CHRA) houses the shaft that connects the turbine to the compressor. It also contains a bearing to allow the shaft to rotate at high speeds with minimal friction, and some CHRAs are water-cooled to protect the turbocharger's lubricating oil from overheating.
What additional components are commonly used in conjunction with turbochargers?
Intercooler, supporting components like wastegate and blow-off valve, and in some cases, a ported shroud for greater resistance to compressor surge and improved efficiency of the compressor wheel.
Explain the purpose of a variable-geometry turbocharger and its benefits in engine performance.
A variable-geometry turbocharger alters the turbine housing's geometry as the engine accelerates to maintain the optimum aspect ratio. This results in reduced lag, a lower boost threshold, and greater efficiency at higher engine speeds.
What is the function of a compressor in a turbocharger system?
The compressor draws in outside air through the engine's intake system, pressurizes it, and then feeds it into the combustion chambers via the inlet manifold.
What is the role of the center hub rotating assembly (CHRA) in a turbocharger?
The center hub rotating assembly (CHRA) houses the shaft that connects the turbine to the compressor. It also contains a bearing to allow the shaft to rotate at high speeds with minimal friction.
What is the purpose of an electrically-assisted turbocharger?
An electrically-assisted turbocharger combines a traditional exhaust-powered turbine with an electric motor to reduce turbo lag.
How does a ported shroud improve the efficiency of a turbocharger's compressor wheel?
A ported shroud design allows air to bleed around the compressor blades, providing greater resistance to compressor surge and improving the efficiency of the compressor wheel.
What type of engines are subject to many of the same operating restrictions as gas turbine engines?
Turbocharged piston engines
Which prominent problem was encountered in the early models of the American Boeing B-29 Superfortress high-altitude bombers?
Damage caused by extreme heat and pressure of turbochargers
What was the approach of Lancia's Delta S4 in the 1985 and 1986 World Rally Championships?
Incorporating both a belt-driven supercharger and exhaust-driven turbocharger
In 1849, what did G. Jones of Birmingham, England begin manufacturing?
A lobe pump compressor for coal mine ventilation
Who patented the design for an air mover for use in blast furnaces and other industrial applications in the United States?
Roots Blower Company
In 1878, who obtained the first patent for a screw-type compressor?
Heinrich Krigar
What type of engines have occasionally been used in production cars, such as the 2005-2013 Volkswagen 1.4 litre and the 2017-present Volvo B4204T43/B4204T48 2.0 litre four-cylinder engines?
Twincharged engines
In the 1985 and 1986 World Rally Championships, what was the design of Lancia's Delta S4?
Incorporating both a belt-driven supercharger and exhaust-driven turbocharger
What is the efficiency range of roots blowers at high boost levels?
40-50%
Which type of supercharger delivers a nearly fixed volume of air per compressor revolution?
Roots-type supercharger
What does the GMC rating system for positive-displacement superchargers measure?
Capacity per revolution
How do dynamic compressors achieve pressure increase?
By accelerating air to high speed and then exchanging that velocity for pressure
Which method is NOT used to drive a supercharger?
Hydraulic drive
What advantage do fuels with a higher octane rating provide in supercharged engines?
Resist autoignition and detonation
What is a potential downside of forced induction, such as supercharging or turbocharging?
Increased intake air temperature causing pre-ignition or knocking
In comparison to supercharged engines, what advantage do turbocharged engines generally offer?
More power and better fuel economy
In what applications are supercharged engines commonly found due to the importance of throttle response?
Drag racing and tractor pulling competitions
During which historical period were mechanically driven superchargers used in aircraft engines?
World War II
Why were turbochargers useful in high-altitude bombers and some fighter aircraft?
Increased high altitude performance and range
What advantage did superchargers offer in comparison to turbochargers in terms of layout and construction?
A more compact layout
What distinguishes a supercharger from a turbocharger?
A supercharger is belt-driven, while a turbocharger is powered by exhaust gases.
When did superchargers begin to be used in car engines?
In the 1920s
What is the primary advantage of using superchargers in aircraft piston engines?
To compensate for lower air density at high altitudes
Which type of supercharger delivers an almost constant level of boost pressure at all engine speeds?
Positive displacement superchargers
What is the function of the ported shroud in a turbocharger system?
The ported shroud allows air to bleed around the compressor blades, providing greater resistance to compressor surge and improving the efficiency of the compressor wheel.
What is the purpose of the center hub rotating assembly (CHRA) in a turbocharger?
The CHRA houses the shaft that connects the turbine to the compressor, and contains a bearing to allow the shaft to rotate at high speeds with minimal friction. It can also be water-cooled to protect the turbocharger's lubricating oil from overheating.
How does a variable-geometry turbocharger maintain optimum aspect ratio at different engine speeds?
By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum, resulting in reduced lag, a lower boost threshold, and greater efficiency at higher engine speeds.
What is the role of an electrically-assisted turbocharger?
An electrically-assisted turbocharger combines a traditional exhaust-powered turbine with an electric motor to reduce turbo lag, improving engine performance.
What additional components are commonly used in conjunction with turbochargers?
Commonly used additional components are intercoolers, which are radiators used to cool the compressed air, and supporting components that enable the engine to be driveable in a range of load and rpm conditions.
Study Notes
Supercharging and Turbocharging Overview
- Roots blowers are about 40-50% efficient at high boost levels, while dynamic superchargers are 70-85% efficient.
- Positive displacement pumps deliver a nearly fixed volume of air per compressor revolution, with the most common type being the Roots-type supercharger.
- The GMC rating system for positive-displacement superchargers is based on the capacity per revolution, e.g., a 6–71 blower pumps 339 cu in (5.6 L) per revolution.
- Dynamic compressors rely on accelerating air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down.
- Common methods of driving a supercharger include belt, direct drive, gear drive, chain drive, variable speed ratio, and electric motors for electric superchargers.
- Fuels with a higher octane rating can resist autoignition and detonation, allowing for increased supercharger boost and engine output.
- Forced induction, such as supercharging or turbocharging, increases the intake air temperature, which can cause pre-ignition or knocking, reducing engine performance.
- Turbocharged engines use energy from exhaust gas, producing more power and better fuel economy than supercharged engines but can suffer from turbo lag.
- Supercharged engines are common in applications where throttle response is crucial, such as drag racing and tractor pulling competitions.
- Aircraft engines used mechanically driven superchargers during World War II due to manufacturing advantages, while turbochargers were mainly employed in American aircraft engines for operational range benefits.
- Turbochargers were useful in high-altitude bombers and some fighter aircraft due to increased high altitude performance and range.
- Turbochargers were comparably heavier when turbocharged, requiring additional ducting of expensive high-temperature metal alloys, while superchargers offered a more compact layout.
Test your knowledge of turbochargers with this quiz! Learn about how they work, their benefits, and their impact on engine performance. See how much you know about this forced induction device powered by exhaust gases.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
