Turbochargers Explained

Even though Carnot showed long ago that all engines are doomed to be inefficient due to the law of ever-increasing entropy, engineers have found ways of extracting maximum efficiency from engines through intelligent designs and modifications. One such smart modification is the introduction of turbochargers. In this article, you will find the working of turbochargers explained in detail.

What are Turbochargers?
A turbocharger is a turbine driven air compression mechanism that is used to force pressurized (high density) air into engines to increase their power output. Denser air ingested into engines lets more fuel burn during every compression stroke, which increases the power output of engines through every engine cycle. To put it in simpler words, the engine gets more air to breathe in order to drive the combustion when a turbocharger is fitted in.

The turbine that drives the turbocharger compressor is operated by feedback of exhaust gases from the engine. So the turbocharger mechanism is essentially self propelled by the car engine itself. The turbine that drives the compressor rotates at a speed of about 150,000 rotations per minute. They provide a boost of 6 to 8 eight pounds per square inch (psi) in pressure of air ingested into the engine. As the outer atmospheric pressure is 14.7 psi on an average, with every engine cycle, 50% more air is pumped in. Turbochargers have been known to boost engine power by as much as 30% to 40%. They are fitted in petrol and diesel engines.

These types of engine boosting mechanisms are called 'forced induction systems'. Turbochargers are usually fitted in high performance sports cars. These car parts are developed using light metals, so that they do not significantly increase the overall weight of the car, while boosting its engine power. Turbochargers are also used in airplane and motorcycle engines to boost power output.

Design & Working of Turbochargers Explained
Turbochargers are directly attached to the exhaust manifold of cars. The exhaust gases from the engine pass through a pipe and drive the turbine wheel of the compressor before getting discharged. The turbine wheel drives the compressor wheel fan attached to it, that is connected to the intake manifold. This fan acts like a centrifugal pump, drawing air into the intake manifold and compressing air in the process. This pressurized air is fed to the engine to boost its power output. Since the turbine rotates at very high speeds, fluid bearings are used to support it. Normal bearings wouldn't stand the high friction caused by the rotating shaft. Fluid bearings maintain a constant level of oil around the shaft that lubricates and cools it.

As you can see, turbochargers are driven by a feedback mechanism driven by the exhaust gases of the engine. This feedback does have an effect on the working of the engine as the exhaust gases need to be pushed out more forcefully than before by the engine. Also, the turbocharger takes some time to build enough compressive power and boost the engine power. So the car may experience a 'turbo lag' initially. However, this effect can be reduced by using lighter metals and ceramics in the construction of these turbochargers which reduces the overall inertia. An alternative way is to reduce the size of the turbocharger.

There is another danger of the turbochargers going into overdrive at high engine speeds. To prevent this, most turbochargers have a 'waste gate' that lets the exhaust gases bypass the turbocharger when it goes into overdrive. Some cars are fitted with two turbochargers, one small and one big, that act at different engine speeds. The efficiency of car engines gets reduced at high altitudes as the air gets more rarefied. Therefore, at high altitudes a turbocharger comes in handy by pumping in pressurized air and maintaining engine efficiency.

As a turbocharger vs supercharger comparison would reveal, turbochargers are one type of superchargers developed to boost the efficiency of engines and their power output. Development of such engine power boosting technologies has enabled engineers to extract the maximum power from engines within the limit on engine efficiency, set by Mr. Carnot!