Vehicles
The turbocharger
A wheel spun by exhaust gas at up to about 250,000 RPM, blowing extra air into the engine.
- Shaft speed
- about 100,000–250,000 RPM
- Compressor wheel
- about 40–80 mm across (cars)
- Exhaust gas
- up to about 1,000 °C
- Impeller type
- open, radial compressor
Numbers are rounded, typical values — real machines vary.
Two wheels on one shaft
Hot exhaust gas leaving the engine spins a wheel. On the same shaft, on the cold side, a impeller sucks in fresh air and pushes it into the engine at higher pressure.
More air means more fuel can burn, so a small engine gives the power of a bigger one — and uses energy that would otherwise leave through the exhaust.
Why so fast?
Air is about 800 times lighter than water. To give it a useful push, the vane tips must move at hundreds of metres per second — close to the .
That is why the wheel is machined from solid aluminium or titanium and balanced to a fraction of a gram: at these speeds, a tiny becomes a huge force.
Physics you already know
Air coming out is hot because compressing a gas heats it, so many engines cool it again in an intercooler before it enters the cylinders.