Ever heard the DTC (Delhi) or BEST(Mumbai) or BTIS( Bangalore) buses whistling their way while shifting gears or while halting at the depot or a stop?? If your answer to the above question is yes, then you must have definitely wondered what the whistling is all about.( if your answer is no, then continue reading and next time keep your ears alert for the whistling) Lets get straight to the answer. The whistling sound coming is actually from the blow off valve of the turbocharger in the buses.
The name “Turbo” will bring words like power, speed, awesomeness in your head(only if you are a car maniac; otherwise its just an usual English word). Well then lets get started and explore the Turbochargers and a similar mechanism called Superchargers. But before that lets dig a little into why the above two are needed.
A combustion engine needs power just like our heart needs fresh supply of oxygenated air to breathe. Well, that is for normal functioning of the engine. Analogous to a weightlifter who takes deep breathes before lifting weight, to pump up the power output , air needs to be gushed into the combustion chamber.. This mechanism is employed in high performance sports cars and also in heavy vehicles which need lots of power for their normal functioning. Here the compressor duo come together. Lets start with the supercharger first.
A supercharger is an air compressor which is driven by crankshaft of the engine connected through a belt. What it basically does is increase the density or pressure of the air in the combustion chamber. This gives it more oxygen for combustion which increases the fuel supply and thus increase the power output. A supercharger differs from a turbocharger in one major aspect- the source of energy for their functioning. As mentioned earlier, a supercharger is connected to the crank of the engine and from there is where it gets its power supply. As the engine revs faster , more amount of air is forced into the combustion chamber. Thus a supercharger works right from the lowest rpm to the highest rpm. At the redline it discharges and we get the whistling sound. While driving a supercharged car, you get the kick right from the moment you start accelerating. This is one plus point of the supercharger. However the power boost obtained in a supercharger is quite less as compared to a turbocharger. This is because the supercharger itself consumes the engine power output in its own functioning. Thus the net power output = Engine power output – power consumed by the supercharger. However the power delivery in a supercharger is instantaneous all because of its connection with the crankshaft. Also there is no lag in the supercharger because it delivers power in the low rpm range as well. Natural air which is sucked in is not passed through a cooler before letting it into the combustion chamber and hence it adds up to the engine heat. This is also a drawback of using a supercharger. Using a supercharger is very cost effective way of pumping up the performance of low displacement cars.
Have you ever noticed the Mercedes lineup which has the Kompressor badge on it ?? The Kompressor badge denots the presence of a supercharger in the car. This was in the early 2000’s soon after which they abandoned the supercharger and have shifted to the turbocharger. We’ll get to know the reason for it but before that lets just summarize the supercharger with its pros and cons –
* Cost efficient way of boosting car performance.
* Quick power delivery because of its connection with the crankshaft.
* Power boosting at low rpm ranges unlike the turbocharger
* No lag as that in the turbocharger.
* It acts as a parasite on the engine by using the engine’s power output thus reducing the net power output of the engine thus affecting the performance.
* Using it with a stock pre-built engine it raises reliability concerns because forcing air into the stock engine outside its capacity is likely to damage the engine. Hence it requires that the engine be built from scratch or all the parts be changed with aftermarket high performance parts
A Turbocharger is also an air compressor just like the supercharger with one major difference. It does not use the crankshaft mechanism for its functioning. Instead it is driven by the exhaust gases . Here comes the efficiency. This is one major aspect where it supersedes the supercharger. It runs on the waste exhaust gases fulfilling the double purpose of being self dependent and also reducing the emission of exhaust gases thus increasing the efficiency. The way a turbocharger works is a little different from the supercharger. The exhaust gases let out from the combustion chamber are forced into the turbine chamber . In the turbine chamber , there are two turbines connected through a shaft. The exhaust gases are forced on one turbine due to which it spins thus spinning the other turbine with it . The second turbine starts sucking in air and flowing it to the inter-cooler to cool down the pressurized hot air from which it is passed on to the combustion chamber. Well this is not the end of the story. How much air to suck in is the question here. The turbine chamber is set for a particular threshold pressure exceeding which the exhaust gas is then directly let out of the exhaust system without letting it into the turbine chamber thus stopping the turbo function. At the same time when excess air at high pressure is waiting to enter the combustion chamber and the threshold is reached there is a blow off valve which does it work. It blows of the air outside and at the same time the intake valve closes. This is how exactly the whistling happens. Ever thought that the actual process of whistling on the outside has so many process running within? Well this is how a turbocharger works. Interesting ??
Now lets just conclude this topic with the pros and cons of the turbocharger.
* Use the waste exhaust gases for functioning thus reducing the emission of these gases and also at the same time increasing the efficiency without using the power from the engine.
* Boosting the power of small displacement vehicles significantly compared to the engine size
* Better fuel economy
* Turbo lag- Big turbos take time to spool until they reach a particular high rpm.The turbo does not start functioning at low rpm and starts working only at high rpm when the exhaust air force is adequate enough to boost. They do not work across a wide range of rpm as the supercharger does.
* Traction problem- The moment the engine enters the turbo working rpm range, power is boosted almost instantaneously causing the car to lose traction and slide.
* Soaring temperature- Turbochargers as they work at high rpms heat up and need oil for keeping a check on the temperature. Hence adequate oil lubrication is required unlike the supercharger.
Verdict– Supercharger or Turbocharger??? Well this depends on the application and requirement. Both have their own pros and cons. My personal opinion is TwinCharger. Yes , right. It is a combination of both and Supercharger which works at low rpms and a turbocharger which works at high rpm thus complementing each other’s cons and emerging as a winner. So the next time when you hear a whistling sound, it is the turbo spooling and try to play this entire process discussed above & you will be grinning in no time. Stay tuned to Turbozens for more updates on automobiles and related news and technologies 🙂