Turbocharger: How does it really work....?
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Yes, the turbo uses exhaust to power itself, but because of the increased backpressure, it makes the exhaust VERY hot. A turbo will get up to 200 C hotter than an NA. It will NOT make it cooler. My exhaust hit 850-900 C under full load. If your NA gets that hot, you are too lean.[email protected] said:
The exhaust in a turbo is hotter because it's under much greater pressure to begin with than an NA engine would ever be.Marc Z31 said:
A turbo uses heat energy, thermal expansion in the turbine chamber, to drive the turbine blades. True, turbos have a little backpressure, but it won't add as much heat as you might think. Depends on the turbo itself, at any rate. Too much backpresure and you'll have problems like the DSMs had, with the turbine chamber inlet and wastegate area cracking. In extreme cases, you'll get problems like the RX7 TTs had, with the wastgate melting under high level boost using the stock turbo setup. If you're running 900C under full boost, you're on the edge of melting something yourself. 900C is very close to the upper limit of what any engine can handle. Maintain that for any length of time and you'll start melting pistons and valves.
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[email protected]: I think you should read about how turbos work again. They do NOT use heat energy or thermal expansion to drive the turbine blades. They are simply driven off the exhaust gas flow. Nothing more.
http://auto.howstuffworks.com/turbo.htm
http://auto.howstuffworks.com/turbo.htm
Sorry man, but I'm right. How-Stuff-Works is a kiddie site at best. Ask anybody worth a salt on this site, such as Mike K., how a turbo really works. Exhaust gas velocity accounts for about 30% of how a turbo uses exhaust gas energy. The rest is caused by thermal expansion of exhaust gases in the turbine chamber. A turbo is essentially a heat pump.AZ-ZBum said:
It's a little more involved than that. Just a little matter of physics. But hey, don't beleive me. I've asked some of the resident experts to present the facts. Dunno when they'll be in , eventually I suppose.EZDUZIT said:Hes right AZ, Just light a match under it and watch it spin
I'm not gonna bother arguing my point. I took an entire 4 week class on turbocharger theory and operation, so I think I should know what I'm talking about..........
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You are supposed to be an engineering student! A turbo does not make the exhaust hotter! That would be violating the laws of thermodynamics. In fact it makes it around 300 degrees F cooler!Marc Z31 said:
The turbine extracts energy from the exhaust flow. Some of the drive power is expansion and mass flow accross the turbine, The conversion of heat to drive power. Some is pulse energy due to the tuned effects and harmonics of the system. Some is even accoustic energy. Look at some of your books on turbo machines.
Turbos run a higher EGT Pre turbine all things being equal mostly due to the ideal gas law and backpressure but they are in no way making the exhaust hotter, in fact they make the exhaust cooler.
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Dude, go look at a friggin turbo. Don't study theory. Forget theory. Theory is crap without practical and real world application.[email protected] said:
The gases don't expand in the turbine chamber. If they did, they'd blow those tiny blades apart. Expanding gases create a positive pressure. Pressure alone doesn't spin a turbo. It's the pressure differential between the manifolds and the exhaust port that causes the turbo to spin.
Turbines spin because the air is flowing through the blades. The more air that flows, the faster the turbine spins. All the thermal expansion occurs in the COMBUSTION CHAMBER of the motor. Then, when the exhaust valves are openned, this expanded gas is forced out of the combustion chamber by the upwards moving piston. So all the gases are already expanded as far as they can be. Now they are moving out of the combustion chamber into the exhaust manifolds. But there's more air coming right behind it. And the only place it has to go is out through the turbine. So the blades in the turbine are forced to spin. Because the air in the exhaust manifolds is now slightly pressurized with relation to the air on the other side of the turbine.
btw: a heat pump is NOT a turbo. And vice versa.
heat pump:
http://home.howstuffworks.com/question49.htm
A heat pump is an air conditioner that contains a valve that lets it switch between "air conditioner" and "heater." When the valve is switched one way, the heat pump acts like an air conditioner, and when it is switched the other way it reverses the flow of Freon and acts like a heater.
I guess you might want to ask for your money back for that 4 week course. Use it to buy a book called "Maximum Boost: Designing, Testing, and Installing Turbocharger Systems" by Corky Bell. Once you start reading it, you might have a better understanding about turbochargers and how they work in vehicular applications.
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I think you need to read about how turbos work. I suggest you read turbocharging the high speed internal combustion engine by watson and genoda.AZ-ZBum said:
How stuff work is a sight that explains things to a Jr high level.
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Thats on a diesel engine! In this case turbos help burn the excess fuel reduceing HC and CO but they increse NOX, a much harder pollutant to get rid of. The government never took an official stance on this as far as I know, plese show your source of this information.EZDUZIT said:
Turbos are actualy bad for emmissions, they delay cat light off and increse NOX, hence the lack of CARB approved turbo kits for LEVand ULEV cars.
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I agree. howstuffworks.com is a great site for the basics. But it doesn't go into detail about properly sizing turbos, understanding A/R ratios, spool up times, etc. But for the basics (which is how they work), it's great. It explains completely how a turbo functions and what it's purpose is.morepower2 said:
If you really want to understand turbos and how to properly size a turbo on both the exhaust and intake side, you get the book I mentioned by Corky Bell. It explains a lot more about them as far as properties of adequate sizing and proper cooling of intake charging as well as flow capabilities.
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You are wrong and Ball is right. Read any engineering book on turbomachines. Its expansion accross the turbine that provides the great part of drive force. You are offering a highly simplified view of how a turbo works. Corkey Bell is an engineer but he is also writing in a way that laypeople can easily understand.AZ-ZBum said:
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I have written and published stuff on how turbos work as well that goes into more detail than corkey bells book. In fact I have several articles on turbo sizing in several major magazines. I think I have a pretty decent working knowlege on applications of turbos and so do some of my friends who design turbos for a living.AZ-ZBum said:
You have to take how things work with a gain of salt, its written so a grade school or Jr high level kid can understnad and glean the basics from it. My stuff was written so a high school student that knows some algebra could understand it.
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Read Classic Motorbooks SCC's engine and powertrain handbook, the gist of stuff is in their.AZ-ZBum said:
Its not expanding in the turbine like releasing heat energy, its accross the turbine and extracting heat energy this way. I suggest the before mentioned watson and genoda book specficaly for turbos or any collage engineering text on turbomachines.
You need some higher level math but not alot and they are also boring reads unless you are an engineer or a student and maybe even then. Unfortunatly their are no entertaining high level books on the subject but HP wants me to write one. Turbos for dummeys or something like that.
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[email protected] said:
Here is my $.02 to this.
I agree that a turbo uses heat energy (exhaust gases are forced through the turbine) but could you explain in more detail why it makes the exhaust a bit cooler? Did I read you right? I know that boost (very high), IC, A/F, timing affect how much heat is produced in the exhaust gases.[email protected] said:
Marc Z31 said:
Backpressure as I know it is cause by the turbo piping (Length, angle, IC design, exhaust manifold) and exhaust system (precats, cats). I like the way this is stated,
"Pressurized air is then forced into the engine. Since pressurized air has more oxygen per unit volume (PV = nRT), there is more opportunity for combustion. This additional oxygen can either accompanied by additional fuel for increased power or in some diesel applications, the advantage is in the excess oxygen which allows for cleaner and more complete burning of the fuel, resulting in reduced emissions and increased efficiency."
Az-Zbum said:
True but my Greddy SP make my Twin Turbo sounds stock.
I think you were missing his point? The exhaust gases push the turbine blades which in turn forces the compressor (cold side) to force air to compress. This compression occures in the combustion camber so that more air can fit in the same volume (more O2, bigger bang, more heat) . It's a cyclic cycle of sorts.Az-Zbum said:
Of course this is my opinion which based on my experiance of reading, seeing, and working on my Z. So please don't hurt me!!
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