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Thrust augmentor on a automotive exhaust


proxlamus©

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For those of you who don't know what a thrust augmenter is .. here is a quick diagram.

 

augmentor.JPG

 

Thrust augmenters are commonly used on jet engines and pulse jets primarily to provide additional thrust. I however am thinking a little bit outside the box here, primarily to help evacuate the exhaust and reduce the overall pressure in the exhaust system.

 

Imagine a thrust augmenter on the tip of an exhaust system, something small that can literally bolt on... it would be interesting to see if adding one would

1) reduce the overall pressure in the exhaust system

2) have any beneficial gains (like running an open exhaust)

 

 

or am I dumb

 

On a side note, im not looking to create extra thrust .. any thrust if produced would be so minimal it might be enough to pull 3 bumble bees on a matchbook sled tied to fishing string.

Edited by PrOxLaMuS©
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  • 4 weeks later...
Thrust augmenters are commonly used on jet engines and pulse jets primarily to provide additional thrust.

 

Those are an extension of the combuster nozzle and are part of the combustion process - fuel is generally still burning at the entrance to the thrust augmenter. That example is irrelevant to an internal combustion engine.

 

What you are describing above is a basic merge collector which we all already know about.

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John,

It is not quite as simple as a merge collector. I think you're missing the "cool outside air" entering point in his drawing. I believe what Prox is describing is also known as an eductor nozzle/pump. It's used in shipboard dewatering among other things.

 

The usage in that case is to pump a volume of water through that nozzle, drawing a suction on that secondary ring, which pumps/pulls fluid along with the original fluid pumped in.

The same concept as used on newer diesel exhausts is a method of pulling in a high volume of cool ambient air to cool the tip and exhaust gas leaving the diesel particulate filter at potentially litigious temperatures.

 

-That being said, I don't believe it will work in the manner hoped for. The problem is that your low pressure point is the opposite of where you want it. Unless you plan on running very rich and using a secondary ignition system... like John said

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Well, based on my reading on pulsejets when I should have been doing other stuff (like writing my senior thesis), I'd say that it *will* work, but that any thrust you gain from it will be offset by the drag that it will cause.

 

Also, is car exhaust even hot enough at the tailpipe to make the most use of the augmenter? I know that the pulsing will be fine (if slow relative to what pulse jets operate at), but I'm not sure you're going to have enough heat to make it worth it.

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  • 5 months later...
  • 10 months later...

Its there to cool and dilute the exhaust. When the SCR and Oxide Catalyst systems are working they generate a huge amount of heat and the OEM had to do something to cool the exhaust gasses which are over 900 degrees. Federal law (Dept. of Agriculture - US Forrest Service fire managment).

 

http://www.fs.fed.us/eng/pubs/pdf/08511816.pdf

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Could something like a thrust augmentor be used to help a turbo spool faster?

 

I envision an air pump drawing in outside air, and injecting it into a thrust augmentor positioned before the turbine housing on the exhaust manifold/header making the cold air expand and provide that extra "umphhh" to get the compressor spinning faster. Of course any benefit might be outweighed by the extra drag on the crank by the air pump. And it would make it impossible to use a WBo2 sensor.

 

Or there could be a system that utilizes the EGR pump. Under cruise the EGR is injected into the manifold like usual, but there could be a valve that could divert the EGR through an air-to-air cooler, then injected into a thrust augmentor mounted before the turbine housing when you go to WOT.

 

From what I understand it is pressure differential between the entrance of the turbine housing and the exit of the turbine housing that make the turbo spool, so anything that would increase that pressure differential (like expanding cold air) should spool the turbo faster, allowing large turbo's to be used without much "lag".

 

What I don't know, because I have never studied physics or worked on propulsion engines, is if "thrust" is essentially the same concept as "pressure". But that's just my 2 cents.

Edited by Cannonball89
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John C's comment bears an additional comment. Those are what is called in the compressed air and gas industry 'volume increasers' you see them used in safety blowguns, and that is what function it is performing on that diesel truck exhaust---that little funky divot in the tailpipe extension brought out simply draws in ambient air through the functionality explained earlier, and drastically dilutes the exhaust stream.

 

One thing to think about is that in CAGI (compressed air and gas industry) these are generally classified by ratios, i.e. 7:1 meaning for every one CFM you put in at X psi, you will get 7 CFM out, at a reduced pressure. The nozzle ratios may even be in the CAGI Handbook.

 

Anyway, something that bears investigation is the issue of 'fumes in the interior'---with a proper NOZZLE TAILPIPE on an early S30, you could DRASTICALLY dilute that toxic mess coming out your tailpipe, making your leaking rear deck area less able to suck in noticeable concentrations of malodorous gasses. I think this is something overlooked TOTALLY in the discussion of solutions to the problem. Of course proper sealing is paramount. But since almost EVERY solution involves using a tip extension, why not use a FUNCTIONAL DESIGN to extend the tip, and at the same time dilute that exhaust flow to make any leaks less noxious?

 

Well, off to Funan Digital Mall to go buy my Tom Tom S.E. Asia. Yeah, I'm actually going to buy a GPS...mostly because I'm sick of being tied to taxis and other people driving me around. I want to go out and explore on my own.

 

I digress... ;)

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Stupid thought popped into my head just now... I'm sure that we've all seen the leaf blower superchargers on youtube and been surprised at how well they worked. If one wanted to test this theory that helping to evacuate the exhaust would help, why not put a leaf blower intake on the exhaust pipe and see what happens. Might at least help to prove the concept (might also suck a lot of gas into the exhaust if you have a lot of overlap). Googled "exhaust scavenge pumps" and spent just a few minutes. I did find that there are apparently systems out there for pusher motorhomes (makes sense as they might have 30' of exhaust to get out the back), and a lot of people think they're scams.

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Air amplifiers have been commonly available for many years. I used them in the manufacturing industry for all sorts of things, like moving particles, cooling components... Dyson just started marketing the technology in their blade-less cooling fans. Yes, they might move more air but energy is never free.

 

http://www.amazon.co...17933634&sr=8-2

Edited by cygnusx1
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