AndrewT

I know the basics, like exhaust pressure spins the turbo (turbine) and the flows into a compressor or something and then forces more air into the engine. My question is, where does it force it into? Is there a special valve or something? And where does the turbo tap into the exhaust? At the headers? And how do you control boost? I know its controled by the ECU, but does it just control the amount of air that is allowed to flow into the turbo? Any recommended webstes or books that explains some of this would be appreciated.

The reason I'm asking is that I have a crazy idea for a science fair project (ah, yes, the days of high school). I have a scale model gas-powered car. And I want to turbocharge it. A greatly simplified turbocharged system. Here's the plan, someone tell me if this is stupid:
Take the exhaust pipe, and route it into two (or maybe one) pipe. One pipe is connected to a makeshift turbo (i think i've figured out how to make a very simple one out of plastic or metal or something), which in turn blows the air into the part of the gas engine where the air filter is. More air=more power right??? Now, I was thinking about it, will it matter what temperature the air is? Becuase if the air is directly from the exhaust pipe, it will be hot. Hmmm maybe i can make an intercooler (just kidding). I think this probably won't help to make the car much faster, but hell, its an experiment. And it sounds like fun. Who knows....you see what you guys have gotten me into??? Dreams of K04 turbos dancing in my head...(there's my A4 content) .Anyone have any comments? Suggestions? Thanks.

-andrewt<ul><li><a href="http://freeweb.pdq.net/a41.8tq">My Page That Came Out of My Crazy Brain....</a></li></ul>

markbradford

.....you must also increase the amount of fuel injected. The increased pressure allows more fuel to be ignited=more power. Does your model automatically regulate the air/fuel mixture?

Good Luck,
Mark

david

How big is this model car? You may have some options canibalizing other toys/models.

Paul F

This is somewhat automatic in a normally aspirated engine. The increased air flow draws in more fuel. On a mdern fuel injected engine however the fuel injection time must be increased through electronic control.

Paul

mitro

There's not enough oxygen in exhaust gases, the exhaust just turns the crank to pump fresh air.

mitro

plus,you need a wastegate or popoff valve or you will get a runaway condition..gogito ergo boom!

Mark K

Well, you've got the basics, but as mitro said, there's not enough oxygen in the exhaust for it to be used as the intake air. If you think about it, if the engine used the exhaust air as the intake air, it would just come back around and it would be an endless cycle.

A turbo has two separate 'chambers', one where the turbine is, which is then connected to the compressor in the other chamber. The exhaust air is under high pressure and temperature, which then turns the turbine. The turbine then turns the compressor, which sucks outside ambient air from the precleaner (air filter) and compresses it - higher pressure. High pressure = more boost = more power per combustion. When you compress air, the temperature increases, that's why the air goes through an intercooler before the inlet manifold. Air to air intercoolers are more effective than air to water intercoolers.

So now you have cooler and more compressed air going into the manifold = more oxygen = more power again.

HTH,
Mark

Geza

ideal gas which conforms to the ideal gas equation: PV=nRT where P=pressure, V=volume, n=moles(sort of a unit of mass), R=ideal gas constant, T=temperature. Rearranging this equations we see that n=PV/RT. Therefore, in the case of an internal combustion engine (where the volume is basically constant at BDC (or wherever the intake valve closes), the amount of mass in the cylinder is increased as the pressure of the air is increased and the temperature of the air is decreased; hence the use of a turbocharger and a charge cooler (intercooler). Since it is the mass of air (not volume) which controls combustion, the more mass of air in the cylinders, the more powerful the combustion. However, in order for proper combustion to occur, the correct amount (mass) of fuel is required in order to maintain the stoichiometric ratio (air/fuel ratio - as I recall it is around 14 or 15:1). Forced induction engines are required to control fuel flow as a function of changing boost (hence mass flow) conditions.

Boost is generally controlled by a wastegate, which regulates the amount of exhaust gas which enters the turbine side of the turbocharger. Regulating the flow(or energy)into the turbine regulates the amount of energy which can be extracted to compress the intake air on the compressor side of the turbocharger.

A blowoff valve and/or bypass valve serve a different function. For example, your driving in 2nd gear WOT. High pressure boosted air is flowing like mad through your intake and into your engine. Now it's time to shift to 3rd. What happens is (hopefully) you lift off the throttle to make your shift. As this happens, the throttle plate closes abruptly, stopping the flow of this high pressure intake charge. The intake charge slams against the throttle plate causing a massive pressure pulse to occur. This pressure pulse, if not releived can (at best) cause the compressor to slow down or stall; at worst, it can blow up varions plumbing bits in the intake tract. A blowoff valve is like a pressure relief valve which exhausts excess intake pressure to the atmosphere. A bypass valve bleeds the excess pressure by recycling it to the intake side of the turbocharger compressor. I gotta stop now, but hopefully, some questions were answered.

Regards,
Geza
99.5 Avant 2.8qMS
97 Boxster

AndrewT

Ahhh i get it! Thanks a lot guys! Hmm maybe I'll figure something out. I'll let you know.