Talk:Turbocharger
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[edit] Reats?
Can someone besides me start deleting the pointless, meaningless statement "turbochargers are reats" every day?
I requested for the page to be protected but some admin refused as per below. --Baldur 22:05, 8 December 2006 (UTC)
[edit]
semi-protect. Constant IP vandalism. Baldur 10:48, 8 December 2006 (UTC)
There is not enough recent activity to justify protection at this time. Just watchlist and revert any vandalism. Nishkid64 15:01, 8 December 2006 (UTC)
- Hi, I agree with Nishkid's decision not to protect, but have watchlisted it and will block vandals and/or semi-protect as appropriate. | Mr. Darcy talk 22:23, 8 December 2006 (UTC)
[edit] Blow-Off Valves?
I think that someone should perhaps add a section on blow-off valves, what they do, how they work with the turbocharging system.. etc
Dump valve and Blow off valve don't serve? This article is plenty long enough already. --Baldur 22:07, 8 December 2006 (UTC)
[edit] Constant Speed Turbocharging ?
Is it a revolution in Turbocharging (see http://abgasturbomaschine-extrem.de) ? Look the german discussion page.At the petrol engines you can use the compressor wheel as turbine wheel in the part load range, if you place variable guide vanes above the shroud of the compressor wheel entry. This variable guide vanes replaced the throttle valve of the petrol engines.
[edit] TURBOBRAKE
The first truck engine brake which operate with active turbocharging in the braking mode (look the german discussion page).
Please people, stop adding information that isn't factual. The Porsche 911 was not the first gasoline car with a VNT turbo!
I'd like to make a suggestion that should be added to the turbocharger and supercharger articals.
The most efficient use of fuel is going to be achieved when the length of the power stroke is long enough to take 100% of the power from the working fluid. At this point the pressure in the expansion chamber will be at atmospheric pressure. If the engine does this then it will not need a muffler.
There is going to still be energy that can be salvaged... this is because the gas will be hot. One way to get this energy is with a sterling cycle and another would be to say inject a bit of water into the gas to cause it to cool and contract.
The turbocharger does the opposite. It sacrifics fuel efficieny in order to obtain more power from the engine.
The articals on the Miller and Atkinson cycle should also be altered to reflect this observation. In fact, this is exactly what the Atkinson cycle engine is all about.
A good idea would be to calculate the exact amount of lost power given the boost. This will be determined by integrating the pressure verses missing stroke length because the greater the boost the greater the exhaust gas pressure when the exhaust valve opens. In non-piston engines - its still the same.
Some of this energy is going to be recovered by the turbocharger of course. It acts as a turbine and should be able to achieve about 55% efficiency which is pretty close to what the Brayton Cycle allows. Dumping that recovered energy back into compressed working fluid is ok but I suspect that not much of the energy is actually recovered in practice. The amount achieved in convetional engines should also be in this artical.
If the artical were to include this then I think it would be greatly improved and would be much more authoritive.
Another idea that might have merit is that if the turbine in the exhaust gas stream were to say run a generator then the electricity from this generator could be used to say crack water into Hydrogen and Oxygen which could be fed back into the engine as fuel. I don't know how much energy could be recovered this way. Nevertheless, the artical IMHO should be addressing these issues.
You made several good points, but a couple were incorrect:
If all the energy from the working fluid was extracted, it would be at atmospheric pressure AND temperature. Don't forget that gas law says they're related. There would be no leftover energy, assuming it was possible to have separate compression and expansion ratios to allow all the energy to be put to work. Even then, this theoretical engine could not run at a very high RPM, because of the inevitable stroke length and because the charge takes a certain amount of time to fully combust.
What the Miller cycle is about is compressor efficiency. A reciprocating piston is actually a horribly inefficient compressor, and the compression stroke is the least efficient cycle of the typical four-cycle engine. What the Miller cycle aims to do is use a better compressor (a mechanical supercharger) to do some of the work that the piston would normally do. That is why that engine is 15% more fuel efficient than an Otto-cycle one.
And in fact, that is why a turbocharged engine is still very efficient. The compression ratio of the pistons is lowered (they do less work compressing the charge), and a turbine takes over the rest. A turbocharger's compressor efficiency can be as high as 70-85%, and refers to how much energy goes into raising the pressure compared to how much energy is wasted as heat.
It would be ideal then, following these ideas, to have a piston-type engine with a compression ratio of 2:1 or even 1:1 and an expansion ratio of, say, 20:1 or higher, and have a turbocharger (or supercharger) do most or all of the compression. It would be like the Maxwell cycle on steroids. This way, the energy of combustion could be more completely used to turn the crankshaft instead of being wasted in another cylinder compressing the charge.
re:turbo/air intake if you increase the air intake to a turbo diesel engine and increase the exhaust size to remove emissions quickly would this improve fuel consumption
the fans who have their engines converted/turboed call the subject "forced induction" on forums, and the turbo kits available would usually have intercoolers to cope with overheating.
(!) An intercooler removes thermal energy from the asperated air caused by the pressure increase (a temperature differential increase is caused between the ambient and compressed air because there is more air in the compressed space) to allow more oxygen molecules into the combustion chamber at the same pressure. It is NOT installed to cope with overheating.
Now increasing the power of your engine would soon make you strenghten your brakes, then change your gearbox and put on flaps on the rear end to keep the back of the car pressed down escaping from lift off...
[edit] Fuel economy vs. huge engine?
I think it's worth noting that a turbo engine can achieve better economy with the same power, although possibly with a worse powerband if compression is lowered, than a larger engine. This is especially true for cars with aftemarket turbos, where fuel mileage remains unchanged in highway and careful city driving, despite the increased (peak) power. It is also worth noting that the brake specific fuel consumption (gal/hp, if you will, BSFC) of a turbo engine is often higher, but only under boost, due to the fact that richer air-to-fuel ratios are usually required to ward off knock and high EGTs.
A little peice of trivia is that backpressure can reduce stress on your connecting rods, or so I hear. I don't have anything to back that up though.
--Natesully 06:14, 27 January 2006 (UTC)
[edit] 911 turbo info is correct.
Baldur said: "Please people, stop adding information that isn't factual. The Porsche 911 was not the first gasoline car with a VNT turbo!"
Well, I added the comment on the 911 and have re-added it since it is correct. The Porshe (997) 911 turbo is the first "high production petrol car" to have VGT turbochargers. Only 500 Shelby CSX-VNTs were ever produced, including prototypes, that is not high production!
So Baldur please don't remove information that is factual. However if you can show me another HIGH PRODUCTON petrol car with VGT’s prior to the 997 turbo’s production let us know.
- I'd just like to point out that in addition to the Shelbys, a number of other cars were made by CHrysler with the VNT. This includes the 1990 Shadow ES (141), Shadow Competition (27), Daytona Shelby (536), Daytona C/S (21), and LeBaron GTC (25). How many Porsche 911 Turbos were made in 1997? How do we distinguish production from high production? I'd argue that the Porsche 911 Turbo is NOT a high production petrol car, period, any more than a Dodge Viper is; and that in any case, the first PRODUCTION CAR to have a VNT was indeed made by Dodge a full 14 years before Porsche.
- Additional: sorry, I am showing Porsche 911 turbo sales, according to Automotive News, at 291 units for the first ten months of 2005. Perhaps they sell double that number in Europe, but I fail to see how the Porsche 911 Turbo can be called high production while 1,250 Dodges are not. The CSX was simply a trim line of Dodge Shadow, after all.... no shame in picking up a technology someone else has used before, and presumably making it better. (I'll add that this year, only 80 have been sold from January to October 31 in the US.) I always assumed "high production" started around 50,000 units.
[edit] Subaru
I'm pretty sure that Subaru doesn't make any sequential-turbocharged engines.
[edit] Fuel Efficiency section
I noticed the reference to a 'Clean Up' being required and at first wondered why - there seemed to be lots of great info.
However I feel that it is the tone of the Fuel Efficiency section in particular that is not up to encyclopedia standard. Some of the assertions about the air quality in California "forced" by running on a richer mixture (91RON petrol) sound a little suspicious. Firstly, does the engine management system adjust fuel mixture in response to pre-ignition detected by knock sensing, and to control combustion temperatures as suggested? Or, does the engine management system instead compensate by retarding the ignition timing (this is my understanding?)
Tone, by itself, is probably not important. But tone serves to indicate the calibre of the information. It is harder to trust information that is written informally or that targets a particular 'agenda'.
Thanks! -Alex 203.173.147.117 10:35, 23 May 2006 (UTC)
- Agree with you, Alex. Also of course running a rich mixture doesn't exactly reduce emissions! Turbochargers nearly always run with higher octane because it greatly increases the power you get.
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- Note - use of higher octane is in order to avoid knocking 71.172.23.39 18:44, 28 November 2006 (UTC)
I fixed the section, but now I'm concerned that in order to accurately explain some of the concepts represented there I've had to repeat or redefine terms mentioned in other sections: Thermal efficiency, turbocharger sizing, intercooling and so on. I would really like to make some new sections devoted entirely to these specific ideas and eliminate some of the repetition throughout many parts of the whole article. Then I could add the section on blow-off valves without it being "tacked-on." What do you think? I appreciate your input.
-Brian
INTAKE OPTIMISATION
I've just got a new mazdaSpeed6 and Iam very pleased with it. I would like to modify the air intake but with more knowledge about volume and velocity of air requirements to really optimise the result. Any suggestions please
Denis
- Shouldn't that be a topic for a forum somewhere and not Wikipedia article discussion? Also check under "cold air intake" and see if wikipedia gives you anything. 71.172.23.39 18:44, 28 November 2006 (UTC)
[edit] Subaru sequential turbo
Subaru produced a Legacy sequential turbo car for the JDM. It had two dissimilarly sized turbos, one for low speed, and one that kicked in at higher load and RPM. They no longer produce this car, nor any other twin/sequential/bi turbo cars. Reference: Forced Induction Performance by A. Graham Bell
I believe this was the Legacy RSK - specs here http://specs.amayama.com/specs-subaru-legacy-b4-1998-december/28469/
[edit] Revivions today.
Revisions today:
The exhaust side of a turbocharger is NOT an impeller! It is a turbine. They are opposites, not synonyms. I reworded the article to correct the error. Impellers compress gases. The turbine in a turbocharger is actually decompressing the gas, and that is partially how it extracts energy. The pressure differential across the turbine plays a big part in the energy it extracts. Reference impeller and turbine. Yes, they look about the same, but are different terms and desparately need to be separated.
Took out "sometimes" about speed. It's incredibly typical for turbochargers spin at greater than 100,000 rpm. I'd say darn near every gasoline turbocharger does (besides the most enormous models), and some diesels as well. You can look at about any turbocharger compressor map.
Turbochargers do not compress air in the intake manifold like a Roots blower. They compress the air in the compressor housing, like a Lysholm/Whipple or any other centrifugal supercharger. I reworded this section to more accurately reflect this. I think describing the relationship of the volume flow of the engine to volume flow of the compressor makes far more sense and avoids inaccuracies while still being clear about the relationship of flow and boost pressure. A turbocharger doesn't just "blow" air like a roots blower. There is an important distinction.
Speed of the turbo is not just directly proportional to boost only. It is also proportional to mass air flow. Reworded this as well. That is, 15psi @ 3000rpm and 15 psi @ 6000rpm are very different speeds for the turbo! "directly proportional to boost" implies way too much of a linear and relationship. You may look at any turbo compressor map for verification.
Wording "for example" seemed out of place. It isn't just an example, it is the general case. I wanted to work a link into volumetric efficiency since it is an important concept.
Also worked in a link to wastegate when talking about controlling the speed of the turbocharger, since it really should be mentioned as pretty much the sole means of boost control in any modern turbocharged engine system. No one in their right mind uses intake restrictors or boost dumps anymore.
[edit] Fuel Efficiency Question
This extra waste heat combined with the lower compression ratio (more specifically, expansion ratio) of turbocharged engines contributes to slightly lower thermal efficiency, which has a small but direct impact on overall fuel efficiency.
I'm a little confused here, why does the compression ratio drop with the addition of a turbocharger to the engine? Is it that since the intake air is at higher pressure, you need less volume of air to equal the same mass of air in the combustion chamber? And if this is so, why can't you just program the engine to have a constant compression ratio, regardless of the incoming air pressure? Is it a mechanical limitation, i.e. the combustion chamber can't withstand a higher pressure? Just wondering... - Runch 18:30, 14 August 2006 (UTC)
[edit] Answer to above
The compression ratio doesn't drop automatically with the addition of a turbocharger, but it generally is separately chosen to run a lower compression ratio on any forced induction vehicle.
Since air pressure is increased, cylinder pressure at the same compression ratio will drastically increase. To keep the engine from detonating and/or pre-igniting simply due to the temperature jump of the compression stroke with the extra air (see ideal gas law, charle's law, boyle's law), a turbo car will have a lower static compression ratio compared to a naturally aspirated car. Consider a turbocharged 2.5L I4 running 1bar with a good intercooler may have nearly double the air molecules in each cylinder as a 5.0L V8 producing the same power.
You cannot "program" compression ratio. Static compression ratio is a physical measurement of the displaced volume of the stroke and bore vs. the combustion chamber size with the piston at top dead center.
I think Saab did some development on a car which could change its compression ratio on the fly, but I'm not sure it made it into a production car. For 99% of cars out there, changing compression ratio requires rebuilding the engine with different pistons, rods, and/or crankshaft.
If you could change compression on the fly, yes, you would want to run high compression just tooling around town or cruising, and have it drop at higher load, based on air mass load per cylinder per rev. This would have a very positive benefit for turbocharged cars with regards to fuel efficiency.
Every car's compression ratio is a balance of fuel efficiency and detonation and preignition resistance at high loads. High performance turbocharged cars have a particularly wide range of load from cruising/idling to full throttle operation. Thus, a typical 2.0L turbocharged car is going to have to give up some fuel efficiency compared to a naturally aspirated 2.0L engine so it won't blow up when the turbo kicks in and supplies double the air and double the power.
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- Thanks! - Runch 04:15, 15 August 2006 (UTC)
- This is also why turbos tend to use premium gas!
- Thanks! - Runch 04:15, 15 August 2006 (UTC)
You cannot change the compression ratio by changing rods, shorter rods have disadvantages over longer rods in terms of performance. While destroking the engine will reduce the compression ratio the main purpose of that is to reduce the piston speed and thus increase top end performance. There are 3 methods of altering the compression ratio of an engine. Most common is to fit different designed pistons, another option is to fit a head gasket of a different thickness. Third option is to replace or modify the cylinder head to alter the volume of the combustion chamber. --Baldur 23:16, 30 November 2006 (UTC)
[edit] pump
Why the mention of a pump? Can you turbocharge a pump? If the turbocharger is driven entirely by the dynamic pressure of the exhaust then I would guess it would be less efficient than a mechnically driven supercharger. The big advantage of a turbocharger is it's ability to convert heat into mechanical energy. Taking mechanical energy from the engine in the form of the dynamic pressure of the exhaust has to be less efficient than using a gear or a chain. --Gbleem 15:50, 8 February 2007 (UTC)
- Exhaust gas heat, velocity, and pressure are otherwise completely wasted out the exhaust pipe in a crank-driven supercharged or naturally aspirated engine. Using crank power to compress air directly removes torque at the flywheel. Power used by the compressor is exactly what is removed from the crank. When the exhaust passes through the turbine, its energy is reduced, which accounts for the energy needed to compress the air. The extra back pressure created by the turbine may require some crank power to push gas out of the cylinder, but that is not what accounts for ALL of the energy used by the turbine. Some, or probably most, is taken from wasted energy in the exhaust stream. From there it becomes difficult to directly compare because a turbo car will have different cams and manifolds compared to a blown car. Also, the impeller-based compressors used on turbochargers are much more efficient than a typical roots blower which creates a lot of heat in the intake charge. Some belt drive superchargers use what looks like half a turbo because of this. Lysholm blowers are closer to turbo efficiency, but still take all energy from the crank. --Freonr2 03:50, 16 February 2007 (UTC)
- I think you are agreeing with me. My thought was that if the only energy was to the turbocharger was provided by push of the engine on the exhaust then there would be no advantage to using a turbocharger instead of a supercharger. --Gbleem 14:12, 23 February 2007 (UTC)
[edit] generalization
I did a quick search and found that turbochargers are also used to recover energy in other applications besides internal combustion engines. It seems like they may be recovering more than heat energy. I think the article needs to discuss turbochargers in general and have a section on turbocharging the internal combustion engine. --Gbleem 00:38, 10 February 2007 (UTC)
- Well, that would just be a turbine powered generator, not a turbocharger, would it not? Check out turbine, gas turbine, etc. --Freonr2 03:58, 16 February 2007 (UTC)
- No. For example you use a lot of pressure to run water through a reverse osmosis process. When it comes out the other side it has velocity and heat. You recover the velocity and heat with a turbocharger that helps the pumping of the dirty water comming into the filter. --Gbleem 14:08, 23 February 2007 (UTC)
[edit] New introduction
I replaced the previous introduction for the following reasons:
1. It contained inaccuracies. 2. I think it was to technical. I would be better to explain the thermodynamical principles of a turbo charger in a seperate section of the article.
Please discuss. Ζεύς 11:59, 9 March 2007 (UTC)
- The article should be about turbochargers in general, not just automotive turbochargers or internal combustion engine turbochargers. --Gbleem 08:57, 8 April 2007 (UTC)
