How Does Petrol Turbo Work?

Hello JoicePeter.

Well, I will guess you are asking about a Turbocharger. This link to Wikipedia is a pretty good description of the equipment and how it works.

If this is not what you are looking for, let us know.

Thanks for the reply Doorman.

I had come across this article you mentioned. My doubt is, in Petrol Engines AFAIK fuel-air mixture is the intake. So wont the compression of the intake mixture beyond a level result in pre-ignition of the charge? Even if it is a fuel injection process instead of carburettor, wouldn't the charge undergo pre-ignition at the time of injecting fuel to the turbo compressed air.

Hence how can we increase the efficiency drastically by implementing a turbo charger in petrol engines?

Please pardon me if my doubts are stupid, I am an Electrical Engineer.

I have discovered the well considered text of Wikipedia is usually better than my own words, so I will copy the answer from the Wiki article:

To avoid detonation and physical damage, the pressure in the cylinder must not go too high, to prevent this the intake pressure must be controlled by venting excess gas. The control function is performed by a wastegate, which routes some of the exhaust flow away from the turbine. This regulates air pressure in the intake manifold.

So, in my words, the turbocharger has a method to self-regulate the intake pressure.

Okay Doorman, But I still can't understand how does then the efficiency increases drastically. I came to know about Petrol Turbo from an article about Skoda Octavia RS in India. Its fuel efficiency is almost the double- 21 kmpl with 150 BHP with outstanding performance! Please explain to me in the layman terms: My doubt is if the efficiency could be increased by increasing the intake air pressure, it could be increased by increasing the compression ratio too. But the compression ratio is fixed such that the charge cannot be compressed further, any further compression may result in pre-ignition. Hence how would be the efficiency increased to this extend, if the intake pressure is self regulated? The only possible way I can think of is an isothermal compression of intake air by the turbocharger, again my apologies if I appear stupid, I am an Electrical Engineer.

It is starting to sound as if we are discussing two different systems.

"But I still can't understand how does then the efficiency increases drastically." A turbocharged engine versus the same normally aspriated engine is not more efficient, in terms of fuel economy (Km/Ltr).

Can you explain more fully. I am getting lost. Can someone else chime in?

If I appear stupid, I am just a Doorman!

http://www.reviewcentre.com/reviews870.html

The turbo forces air into the engine,

a normally aspirated engine sucks air into its cylinders as the piston on goes down there is some burnt gases still present in the engine thus reducing the effective cylinder capacity.

in a ideal engine all the burnt gases are removed after each combustion but this never happens.

Even with a well designed exhaust causing scavenging by sonic pressure waves within the exhaust system complete removal of burnt gases is not achieved

To avoid detonation the compression ratio is normally reduced on a turbo engine.

the turbo works at about 7 psi.

it forces fresh air into the cylinder mixed with fuel.

so for ex if the cylinder capacity is say 1 litre if you turbo it the capacity increases over a normal aspirated engine i don't know by how much or care, but lets say to one and half.

that cylinder will produce more power newer now, and yes burn slightly more fuel.

but you now have a choice to use the extra power to go faster or to use the extra power to go at the normal speed but with less throttle thus using less fuel to drive vehicle over the same distance as before using less power,

the result is more distance covered with less fuel used.

turboing increases the engines efficiency the normal petrol engine is only about 24% efficient the rest goes as heat so any improvement is good

http://www.fueleconomy.gov/feg/atv.shtml

http://en.wikipedia.org/wiki/Internal_combustion_engine

http://en.wikipedia.org/wiki/Engine_efficiency

at last a site that tells the truth