Crazy idea.

[Dirk]

Not sure where to post this or if this is the right place to post but here goes:

 

Turbo's and superchargers put a lot of extra strain on an engine and use more fuel but are a good way of extracting more power out of a smaller engine. At least this is my understanding.

 

But what I was thinking was this: What if you were to rig up a super charger unit to work in reverse. In other words use the exhaust to drive the supercharger and put that exhaust energy back into the pully/crankshaft. Sort of a backwards turbo/supercharger

 

Could this be a good way of recycling the exhaust energy with out adding extra strain to the engine?

 

Genius? or Crackpot?

 

Edited December 4, 2009 by Dirk

[crazyman03]

... That's... an interesting idea. I Imagine IF it were possible it would either have to be driven by something like a timing belt. (less slipage) or a chain.

 

Just my addition. IF it were possible.

 

 

Now my thinking about it is.. (and I am NO engineer and simply a weekend mechanic) It would not work. Simply because timing would be inconstant. Well.. maybe not if because it would be adding fuel and igniting at the same position of the piston.

 

 

I don't know. it would be interesting to see what you would get out of it. I imagine you would use the same amount of fuel. If you didn't, there would be less exhaust, and less energy to steal from it? the reverse Supercharger would have to be spinning quite a bit to be able to "Put" energy into the crank instead of steal energy from it.

 

 

-Justin

[crazyman03]

To add.. the more I think about it.. the less likely of it actually doing anything. Least anything of benefit. You would be using the same amount of fuel and wouldn't be getting much if any HP.

 

edit: In my opinion of course. I am just a weekend Mechanic.

 

 

-Justin

Edited December 4, 2009 by crazyman03
edit: In my opinion of course. I am just a weekend Mechanic.

[Dirk]

I thought about the fixed drive aspect and wondered if some sort of rachet system could be used like on the hub of a push bike. Or maybe some sort of clutch system.

 

My engine is 1600cc. At idle it does 900rpm so it would be breathing 720 litres per minute of air?

 

Thats a lot of hot gas not being harnessed right now.

 

The thing I like about this concept is that it is not adding power but recycling unused power.

[Dirk]

In my opinion of course. I am just a weekend Mechanic.

 

Einstein was a patent's clerk!

 

And I'm just a wooden boatbuilder.

[crazyman03]

I can see this concept being used to power an additional Alternator or something of the like. Least that would be the most beneficial.

[Scoobywagon]

I don't see this doing anything for you. Essentially, you're trying to extract energy from the output side of the engine and apply that energy directly to the input side. That's perpetual motion. Won't work.

 

Now....driving a turbo with a belt from the crank and using that to pull exhaust from the engine and push it down the pipe....that might be interesting. You'd essentially be trying to pull a vacuum on the exhaust all the time. You'd DEFINITELY have really excellent scavenging properties

[Dirk]

I don't see this doing anything for you. Essentially, you're trying to extract energy from the output side of the engine and apply that energy directly to the input side. That's perpetual motion. Won't work.

 

Now....driving a turbo with a belt from the crank and using that to pull exhaust from the engine and push it down the pipe....that might be interesting. You'd essentially be trying to pull a vacuum on the exhaust all the time. You'd DEFINITELY have really excellent scavenging properties

 

This doesn't make sense to me. Either they both work or both do not.....?

The theory you are suggesting is exactly the same mechanical setup.

 

Not sure about the perpetual motion thing. The exhaust has energy. Its just not harnessed.

 

(none of my comments are fact or based on knowledge. only speculation)

 

The way I see it is this: Cool air and fuel enter the cylinder. This explodes and forces the piston down. Most of the energy is expended here but not all. What exits the cylinder is a hot expanding gas that still has its own energy. This is the part that is currently wasted. The question is: Is there enough energy left to convert back into a few hp?

Edited December 4, 2009 by Dirk

[GeneralDisorder]

Most supercharger design's are rotary lobe blowers (roots blowers) which can't be driven by exhaust like that. Either that or they are screw style pumps. Being they are generally driven at engine speeds, they are "positive displacement" pumps - the amount of air they flow is almost directly proportional to their speed and there is very little or no "slippage" through the pump - that is that once air goes in, it can't go back the other way. They operate in that 3,000 to 10,000 RPM range - same as the engine. Exhaust gas can't spin the blower with enough force to do any kind of work. Basically the blower isn't efficient enough to extract any useful energy from the exhaust gases.

 

Now turbo's on the other hand are what's known as a turbine. They operate on a completely different principle. The turbine is used to spin a fan which blows air into the engine. The fan must spin VERY fast to increase the pressure on one side of the fan by typically around twice that of atmospheric pressure. The reason it must spin so fast is that the fan is NOT a positive displacement pump. It has to overcome the tendancy for air to slip back across it's blades. The exhaust turbine uses the relatively low density of the exhaust gasses to spin the fan at speeds of around 60,000 to 120,000 RPM - the smaller the turbo the faster it spins as they are limted to speeds below where the tips of the blades break the sound barrier. Obviously you can't really do this by running the fan side of the turbo from the crank pulley unless the fan were very large or it were geared up with a REALLY big gear driving a teensy-tiny gear - which is how it's done in the world of turbine compressors. A 2' diameter gear drives a 2" diameter gear - but that's with compressor fan's that are 6" in diameter. A Subaru turbo has a compressor fan that's about 1" in diameter and as such the size difference of the drive vs. driven gear would be even more radical - that 1" gear would probably need a 10' diameter gear to drive it at the requisite speed with the engine turning 3600 RPM. Not practical.

 

Turbo's work because they are highly effecient at turning the exhaust gases into work - the exhaust gases flow freely by the turbine wheel and impart force to it's blades as they pass. Lobe blowers can't do this - there is too much back-pressure from the positive displacement design and they are very inneficient - requireing 10 HP just to drive them at full engine speeds with a mechanical coupling......

 

GD

[LPGsuperchargedBrumby]

this has been done before...pretty much all the major aircraft engine manufacturers on both sides tried it in varies forms

 

one thing that has been done recently is to use a turbocharger type turbine to drive a alternantor via a reduction drive....

 

altho i don't know how well it would work on anything that uses a throttle that restricts the air flowing thru the engine....the ones i read about where being tested on a nissan diesel truck

[Dirk]

this has been done before...pretty much all the major aircraft engine manufacturers on both sides tried it in varies forms

 

one thing that has been done recently is to use a turbocharger type turbine to drive a alternantor via a reduction drive....

 

altho i don't know how well it would work on anything that uses a throttle that restricts the air flowing thru the engine....the ones i read about where being tested on a nissan diesel truck

 

Sweet! Not so crazy after all!!

[SUBIE-5]

Look up Wright 3350 (cu/in). One version used 3 PRT's (Power Recovery Turbines) geared directly to the crankshaft, each providing an additional 200 HP. How much would you expect from 109 cu/in?:-\

[Dirk]

my figures say 6hp. Thats an extra 10% for me! I reckon thats worth the effort.

 

Plus I'm stoked that the idea actually works!

 

That was a 3700hp engine so they gained nearly 20%! Thats not bad.

Edited December 5, 2009 by Dirk

[NorthWet]

Thread resurrected from near-death...

 

A recent perpetual motion thread got me to notice this thread, and I thought that I would throw in my 2 cents. I had seen mention of turbo-compound engines (what we are really talking about here) some years ago, and thought that it was a neat idea, if somewhat difficult to implement. It is commonly used on industrial diesels, including some by Detroit Diesel and Scania.

 

This is not perpetual motion, and it is not, if done correctly, stealing energy from the engine to try to give it back to the engine. The energy comes from the residual heat energy in the exhaust stream, heat that otherwise just goes out the tailpipe.

 

Implementation is tricky because of the reduction gearing needed to turn the high rotational speed into something the engine can accept.