exhuast ...suction charging... 4

[marcusaurailius]

I have been thinking about this for a while now, and was wondering if the, ..air flow .. under the car, can be used to make the exhuast gasses travel faster,so that ..more..air can be sucked out off the cylinders, to help the ..scavenging,of the combustion chambers
the air would have to be funneled into a ..venturi.. shape , then put in to the exhaust pipe,to speed the air up,relative to the vehicles speed,
any help woould be much appreaciated
Marcus Aurailius

 

[patprimmer]

The venturi principle as been understood for a long time and i the basis for the operation of a carburettor.

It can only work if the fluid doing the pumping is flowing faster than the fluid being pumped.

Exhaust gas normally travels a lot faster than a cars road speed.

I strongly suspect that collecting air over a very large area and concentrating it down to a small area to increase speed will consume more power that the scavenging produces.

Tuned length exhaust headers, tuned length variable inlet runners, high compression, pent roof 4 valve head design and variable cam timing all combine to give good scavenging, so there is little room for furter improvment.

Regards
Pat
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[marcusaurailius]

Pat, i take in what you say, but i was thinking more down the lines or slower engine speeds, .
this is where a 2 valve engine is ..off cam.. and was thinking,that if the gas could be ..pulled.. out sooner, then the engine would come on cam earlier,.
tuned lenght manifolds,ex/in, can only work best at a certain r,p,m.
what i am thinking is to try and give the engine a help before it comes on cam,.
has any one got any figures as to what speed the ex gasses are traveling at,
in a 2.6 engine ,at various r,p,m./load throttle openings,.
if the speed of air is ..then greater.. than the ex gas speed,then one will have a suction scavenging effect!!
Marcus

 

[Bribyk]

I have heard of this being used on race bikes, putting the exhaust in a low pressure region behind the seat to put some negative pressure on it. If the exhaust is flowing faster than the bike then you would get some thrust from placing the exhaust there. Not much effect but every little bit helps in motorsport...

 

[evelrod]

The idea is not new, as Pat sorta hints at. However, your about 180 off. In most of the prototype classes and some of the sedan classes, Trans Am, Le Mans, etc. the exhaust outlets are placed under the rear of the car, usually in some sort of "tunnel" or ---senior moment, I cannot think of the word for it---Anyway, exhaust outlets are in that 'low pressure' area to aid in increasing under chassis airflow, extracting more air from beneath the chassis thereby increasing downforce. It would also decrease overall aero drag a small and probably insignificant amt. (I have never seen any studies on that aspect, however).
Exhaust gas velocity can easily be many times the speed of the vehicle, excepting a supersonic jet car, perhaps. Only one of them that I know of.

Rod

 

[ivymike]

a designosaur friend of mine with several decades of aircraft experience has on many occasions told me that it is possible to make engine ducting which results in positive thrust (vs. drag). This seems consistent with what you're describing, Rod.

 

[ivymike]

um, cowling.

 

[JohnLear]

Might not placing the exhaust outlet in an area of low pressure (e.g. behind the seat / rider on a racing bike) help to 'fill' that area of low pressure, and thus (slightly) decrease drag?

I've always assumed this was why so many racing bikes have such high and centrally located exhaust outlets, i.e. so exhaust gas can slightly raise the pressure seen in what would otherwise be the area of lowest pressure (probably still would be...).

 

[marcusaurailius]

Thanks all off you who have taken an intrest in this post,
I have been trying to find articles relating to this form of suction for a while now,.

But all of the ones i seem to find ,all seem to use some form of ..machanical means.., But none that does it the way i am thinking,.
If any one can point the way to any articles on sucking out ex gasses, I will be pleased,.

The idea is to try and get exhaust gas out, using a venturi style/effect ,caused by car speed /air speed ,to feed into the exhaust,about 3 ft before the outlet of the exhaust,thus ..sucking.. the exhaust gasses out

I am not really interested in top end power, but think that this idea could make the engine pull better at low revs,.
At low revs , small to medium throttle openings,the exhaust gas that comes out of the tail pipe , does not seem to be going that fast,.

This is bourne out by the fact that one can feel the pulses on one,s hand,.and do not seem to have v much speed with them,. {it is a lot faster at the exhaust valve end though],

So if these gasses are slowish, then a venturi effect,with higher air flow , should be able to ..speed them up thus extracting them faster !!!

High lift/long duration cams ,loose power low down,/gain higher up, so I am trying to create the best of both worlds

any help is good help

Marcus







Marcus

 

[Bribyk]

The new Duramax diesels have some sort of venturi on the end of the exhaust pipe and rumour has it they overheat or something if it's removed. I would assume the venturi helps with emissions because its been added since the new regulations. Anyone have some real info/insight on this?

 

[rmw]

When I was a college kid, venturi type tail pipes were sold as a performance enhancer in place of the standard type tail pipes on Volkswagen engines. I don't know if they really worked or if it was the placebo effect due to the fact that I as a poor college boy had spent real money on them, but I always had them.

rmw

 

[thruthefence]

There are a couple of aircraft out there that place the exhaust in ducting that draws out the spent cooling air from the air cooled engine. It's called an "augmenter exhaust"
Aero Commanders, older Cessna 310's use it.

 

[PedroCG]

marcus, at low revs the car is moving slowly... if you slow the gases with an expanding pipe for example the losses in the expansion would probably be bigger than the gains in pressure drop

 

[marcusaurailius]

Pedro CG i wont be using an expanding pipe, the air from the collector box Im going to make, will feed into the exhaust pipe, about 2 foot from the end

but will try it out first by just putting it on the end of the pipe with an adaptor pipe,

can only try, nothing to loose, may be some thing to gain,

will be doing this in a few weeks if i get the time, but will tell if it any good

thanks every one for the intrest

Marcus

 

[Fourman]

Exhaust extractors have been around for a long time.They were popular for british sports car going back into the 1950s. A search for the Alextractor by Alexander Engineering Co. should give some useful information.
They work as you describe above, using air movement under car.

 

[marcusaurailius]

Fourman, thanks for the info, went and had a look, its no what i am making thought.
i am half way there now, i got a ..flat box.., 2, ft wide, 2, inch deep, radiusd edges, tapering back to a 2,5in pipe outlet.
this is my ..air scoop.. which will then be put on to the wnd of the exhaust to try it out
if it is any good, then it will be piped into the exhuast further forward
can only try, but thanks for the info,
i think i will finnish it soon, and will let you all no of ..what it did???/

Marcus

 

[turbocohen]

Here is some flashy BS on the subject.. I stress BS.

http://www.impulsengine.com/how/header.shtml

Here is a decent article with some science behind it.

http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/index.html

 

[patprimmer]

Re the aircraft anology, generally aircraft have a high air speed vs engine speed when compared to a car. They also operate at much more constant speed.

Regards
Pat
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