A turbocharger is a device used to increase an engine’s efficiency. It increases the amount of air entering the combustion chamber. A turbocharger is responsible for better performance and achieving higher sudden speed. Today in this article I will discuss the working principle of a turbocharger in a diesel engine. 

Working Principle of a Turbocharger in a diesel engine

 

Working Principle of a Turbocharger in a diesel engine.

The turbocharger is bolted to the exhaust manifold of the engine. The exhaust from the cylinders spins the turbine, which works like a gas turbine engine. The turbine is connected by a shaft to the compressor, which is located between the air filter and the intake manifold. The compressor pressurizes the air going into the cylinders. The exhaust from the cylinders passes through the turbine blades, causing the turbine to spin. The more exhaust that goes through the blades, the faster they spin. On the other end of the shaft that the turbine is attached to, the compressor pumps air into the cylinders. The compressor is a type of centrifugal pump. It draws air in at the center of its blades and flings it outward as it spins.

In order to handle speeds of up to 150,000 rpm, the turbine shaft has to be supported very carefully. Most bearings would explode at speeds like this, so most turbochargers use a fluid bearing. This type of bearing supports the shaft on a thin layer of oil that is constantly pumped around the shaft. This serves two purposes: it cools the shaft and some of the other turbocharger parts; and it allows the shaft to spin without much friction.

 

To reduce the inertia of the turbine and compressor is to make the turbocharger smaller. A small turbocharger will provide a boost more quickly and at lower engine speeds, but may not be able to provide much boost at higher engine speeds when a really large volume of air is going into the engine. It is also in danger of spinning too quickly at higher engine speeds when lots of exhaust passes through the turbine. A large turbocharger can provide lots of boost at high engine speeds but may have bad turbo lag because of how long it takes to accelerate its heavier turbine and compressor.

 

Too much boost- 

With air being pumped into the cylinders under pressure by the turbocharger, and then being further compressed by the piston, there is more danger of knock. Knocking happens because as you compress air, the temperature of the air increases. The temperature may increase enough to ignite the fuel before the spark plug fires. Cars with turbochargers often need to run on higher octane fuel to avoid knock. If the boost pressure is really high, the compression ratio of the engine may have to be reduced to avoid knocking.

 

Turbo lag- 

One of the main problems with turbochargers is that they do not provide an immediate power boost when you step on the gas. It takes a second for the turbine to get up to speed before a boost is produced. This results in a feeling of lag when you step on the gas, and then the car lunges ahead when the turbo gets moving. One way to decrease turbo lag is to reduce the inertia of the rotating parts, mainly by reducing their weight. This allows the turbine and compressor to accelerate quickly, and start providing boost earlier.

 

Optional turbo features–

In a diesel engine, there are a lot of optional turbo features available. The extra optional features are- 

 

The wastegate-

Most automotive turbochargers have a wastegate, which allows the use of a smaller turbocharger to reduce lag while preventing it from spinning too quickly at high engine speeds. The wastegate is a valve that allows the exhaust to bypass the turbine blades. The wastegate senses the boost pressure. If the pressure gets too high, it could be an indicator that the turbine is spinning too quickly, so the wastegate bypasses some of the exhaust around the turbine blade, allowing the blades to slow down.

 

Ball bearings- 

Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. But these are not your regular ball bearings — they are super-precise bearings made of advanced materials to handle the speeds and temperatures of the turbocharger. They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller, lighter shaft to be used. This helps the turbocharger to accelerate more quickly, further reducing turbo lag.

 

Intercoolers- 

When air is compressed, it heats up and when air heats up, it expands. So, some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine. In order, to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure.

An intercooler or charge air cooler is an additional component that looks something like a radiator, except that air passes through the inside as well as the outside of the intercooler. The intake air passes through sealed passageways inside the cooler, while cooler air from outside is blown across the fins by the engine cooling fan.

The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it goes it the engine. This means that if the turbocharger is operating at a boost of 5 N/cm2 cm- the inter-cooled system will put in  5 N/cm2 of cooler air, which is denser and contains more air molecules than warmer air.