Tuesday 8 March 2016

Turbochargers

What is a Turbocharger?

When someone asks you a way of increasing the power of an internal combustion engine, then immediately we start thinking about turbochargers. It can considerably increase engine power without adding any significant weight.

Turbochargers forcefully introduce more amount of compressed air into the combustion chamber. This allows the fuel injection system to supply more fuel into the cylinder and therefore increase the engine horsepower. The advantage of a turbocharger is that it increases the power-to-weight ratio of the engine, making it more efficient.

Who Invented Turbochargers?

The first turbocharger ever designed was patented by Alfred J. Büchi on November 16, 1905. He was a Swiss automotive engineer and is known as the inventor of turbochargers.

How does a Turbocharger work?

A turbocharger is run by the exhaust gases coming out of the engine. The exhaust gases rotate the turbine, which in turn runs the compressor. The compressor draws more amount of air and compresses it. The compressed air is cooled and sent to the inlet manifold. Turbochargers can spin up to speeds in the range of 1,00,000 to 1,50,000 RPM.

The normal atmospheric pressure of air is 1.013 bar. A typical turbocharger can provide a boost of 0.4 to 0.6 bar. Therefore it can provide almost 40% to 50% more air than an engine without a turbocharger.

Turbocharger Design and Operation:

One can find a turbocharger installed in the exhaust manifold of the engine. Turbocharger is made of a turbine and a compressor, both connected with a single shaft. Most of the modern day turbochargers are provided with a wastegate in the turbine side.




The exhaust gases flow through the turbine blades and spins the turbine. The compressor on the other side also starts spinning at the same speed as that of the turbine. The compressor draws the air in and then compresses it due to its centrifugal action.

The cool air entering the compressor is squeezed and heated and then it is blown out. The compressed air passes through a heat exchanger to cool it down, as cooler air has more density.

Now the cooled, compressed air is sent to the engine intake. More amount of air helps in faster combustion and also allows more fuel to be injected inside the combustion chamber. As more fuel is burned, more power is produced.

Purpose of a wastegate in a Turbocharger:

At higher engine speeds, the turbochargers spin faster than in a normal speed. This can result in a higher boost pressure from the turbocharger. Wastegate prevents the boost pressure to cross the maximum limit by bypassing the exhaust gases to the exhaust pipe. This also prevents the turbine from spinning at speeds higher than its maximum limit.

Turbo Lag:

One of the main disadvantages of using a turbocharger is that they don’t provide immediate boost pressure as soon as the engine is started. It takes some time to produce enough exhaust gas to spool the turbines fast enough to generate the required boost pressure. This is known as turbo lag.

Turbo lab can be reduced by using a smaller turbocharger in which boost pressure can be created at lower speeds. But smaller turbocharger won’t be able to generate the required boost pressure at higher speeds and there is more risk of damage to the turbine at higher speeds.

To overcome the problem mentioned in the previous paragraph, some cars are installed with 2 turbochargers. One small sized turbo to provide boost pressure at lower speeds. Whereas the other turbo which is larger, provides boost at higher speeds.

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