A turbocharger is a device that helps an engine make more power by forcing extra air into the cylinders. More air means the engine can burn more fuel in each combustion cycle, which increases power without making the engine much larger. The key idea is that the turbocharger uses energy that would normally leave the car as hot exhaust gas.
This makes it an important example of improving engine performance by recovering waste energy.
A turbocharger has two main wheels mounted on the same shaft: a turbine wheel and a compressor wheel. Exhaust gas spins the turbine, the turbine spins the shaft, and the shaft spins the compressor that pushes intake air toward the engine. Because compressed air heats up, many turbocharged engines use an intercooler to cool the air before it enters the cylinders.
Boost pressure, wastegate control, and airflow design all affect how quickly the turbo responds and how much extra power the engine can safely produce.
Key Facts
- A turbocharger uses exhaust gas energy to spin a turbine connected to an intake air compressor.
- More intake air allows more fuel to burn, increasing engine power output.
- Boost pressure is the extra intake pressure above atmospheric pressure.
- Absolute intake pressure = atmospheric pressure + boost pressure.
- Compressor pressure ratio = outlet absolute pressure / inlet absolute pressure.
- Power gain is limited by heat, fuel delivery, engine strength, and knock resistance.
Vocabulary
- Turbocharger
- A turbocharger is a device that uses exhaust gas to drive a compressor that forces more air into an engine.
- Turbine
- A turbine is a wheel spun by flowing exhaust gas, converting gas energy into rotation.
- Compressor
- A compressor is a wheel that increases the pressure and density of incoming air.
- Boost Pressure
- Boost pressure is the amount by which intake air pressure is raised above normal atmospheric pressure.
- Intercooler
- An intercooler is a heat exchanger that cools compressed intake air before it enters the engine.
Common Mistakes to Avoid
- Thinking the turbocharger is powered by the battery, which is wrong because the turbine is driven mainly by exhaust gas flow.
- Confusing boost pressure with total intake pressure, which is wrong because total absolute pressure includes atmospheric pressure plus boost.
- Assuming hotter compressed air is always better, which is wrong because hot air is less dense and can increase the risk of engine knock.
- Ignoring turbo lag, which is wrong because the turbine and compressor need time and exhaust flow to speed up before full boost is available.
Practice Questions
- 1 A turbo engine has atmospheric pressure of 101 kPa and boost pressure of 60 kPa. What is the absolute intake pressure?
- 2 A compressor takes in air at 100 kPa absolute and delivers it at 180 kPa absolute. What is the compressor pressure ratio?
- 3 Explain why an intercooler can help a turbocharged engine make more power even though the turbocharger has already compressed the air.