Negative Pressure Supercharging... righto then

[Mike Gayner]

Have a look at this...
http://www.impulsengine.com/kits/index.shtml

They call it "Negative Pressure Supercharging" and to me it looks like a load of bollocks. There are so many problems with this system I don't know where to begin.

The whole system relies mainly on an extremely innefficient exhaust system to create a negative pressure during scavenging, and then a special cam timing to trap the negative pressure inside the cylinders. Please note that I'm not the one who coined the term "negative pressure" as I'm well aware there is no such thing.

Now first of all, even if you were able to create an intense vacuum inside the combustion chambers, it would be enough to force an extremely small amount of air into the cylinders. Just think about it - the low pressure is created when the piston is very near TDC, meaning the low pressure zone would be very small when compared to the volume of the cylinder at BDC.

Even assuming this low pressure stuff worked, the cam timing would absolutely destroy any power up high in the rev range. Next on the list is the induction system. This is a naturally aspirated engine (despite the title) and relies on a hot air charge to create a faster "explosion" (once again not my words) in the combustion chamber, and a low water temperature (using a flow restrictor and no therostat) to keep combustion temperatures down and reduce pinging. Apparently having a high intake temperature yeilds more power due to the fuel "exploding" much quicker in the cumbustion chamber. What a ridiculous idea.

Thoughts on this "supercharger"? Am I missing something or is this thing just plain stupid?

[Kryton]

well considering that they arent available for ANY ford engines, im taking a stab in the dark and assuming its all aimed at Commo drivers.

[needturbo6]

very interesting!! its probably not bs, i hope not. ya gotto have an open mind these days, i think.

i can sorta understand it with its high(hot) and low(cold) pressure theory. its very hard to understand but i think i got a grip of it.

and anyone here a physics expert? i would like to read a constructive post....

[seano14]

2 equal size gas cylinders filled with the same volume of gas are placed in an open field. The temperature of one gas cylinder is chilled to a cold 10°C (50°F) while the other gas cylinder is heated to a hot 121°C (250°F) or to just before it explodes. A spark is used to ignite the hot and cold gas cylinders and both explode with a tremendous force but the hot gas cylinder leaves a larger crater.

i think they need better tests than this backyard style sh#t! :yeees:

[RED_EL_XR8]

Hmm a flow restrictor that reduces engine temperature by 50°C, and no thermostat required, that'd be good, but not in my engine thankyou. 50°C???

[Psycho Chicken]

This gets funnier the more you read into it. Hot air induction? hahaha, ok.

[Panda]

Where to start, where to start....

Exhaust Cycle
The Negative Pressure Supercharging process begins with the exhaust cycle. As the exhaust valve opens the massive gas pressure produced after combustion it has already expended it's energy - driving down the pistonforces itself through a compact header with very small and short pipes. This causes the high pressure gas to compress in the small pipe increasing pressure, reducing flow = no net increase in gas flowand accelerate to a high velocity which is twice the speed produced by typical large pipe headersagain, increasing pressure and reducing flow = no net change in gas flow. As a result a negative pressure is produced behind the high velocity gas in the small pipe which is so strong it reduces the pressure in the cylinder during the exhaust stroke. it is the positive pressure in the cylinder which moves the gas, it does not move on it's own

However, the high pressure gas in the small pipe of the header will remain compressed for only a short distance before it builds up back pressure and restricts the gas flow. nopeTherefore, the small pipe of the header is very short and a megaphone pipe is used after the header to allow the compressed gas in the small pipe to gradually expand into the larger diameter of the megaphone pipe.this does actually work - the venturi effect This allows the exhaust gas to flow only away from the exhaust port at a very high velocity and with no back pressure to restrict the gas flow. this part however is crap

Keep in mind that negative (low) pressure is naturally produced behind all moving objects which travel at a high speedcrap, gasses do not have a mass. The faster the speed of a moving object, the lower and stronger the negative pressure is behind the fast moving object. wrong for so many reasonsThe same principle applies to the gas flow in the primary pipe of a typical headerhorse-shit. The smaller the pipe, the faster the gas speed trueand therefore the lower and stronger the negative pressure is behind the gas flow in the header. false


Overlap Period
At the end of the exhaust cycle during the overlap period, the negative (low) pressure is trapped in the combustion chamber by closing the exhaust valve early before TDC and using low exhaust valve lift. so you close in the cylinder while the piston is still compressingSoon after the exhaust valve has closed, the intake valve opens early before TDC still compressingto allow the negative pressure trapped in the combustion chamber to pull the intake charge into the engine instead of into the exhaust system. crap


Intake Cycle
The intake valve opens before TDC and after the exhaust valve has closed, to allow the negative pressure trapped in the combustion chamber to pull the intake charge into the engine and fill the cylinder very rapidly with a greater volume of air early in the intake cycle. still crapThe intake charge is also increased to a hot temperature atomised fuel is already above it's flash point. Increasing the termerature further will make it ignite, but why do you want this on the intake cycle?to produce more combustion pressure you can't produce compression on the intake cycleand burn faster. little bit true

As the piston moves down the cylinder during the intake stroke, it further reduces the pressure in the cylinder. This pulls an additional volume of hot air into the engine faster than the speed of sound. you're ****ing kidding me aren't youAt the end of the intake cycle the intake valve closes early after BDC same as normalto trap the much larger volume of hot air in the cylinder and prevent the air from being forced back into the intake manifold during the compression stroke. same as normal

Keep in mind that even though hot gas is less dense it explodes with a much greater force because it reaches its maximum pressure much faster than the more dense cold gas. because it is less dense the computer has to swing the Air / Fuel ratio - giving you less fuelTherefore, the engine is able to produce more power with a hotter intake charge because the increase in power produced by the higher combustion pressure and faster burn of hot gas is much greater than the loss produced by less dense hot air.


Combustion Stroke
During the combustion stroke the larger volume of hot air forced into the cylinder by the Negative Pressure Supercharging process produces 2 times more torque from idle to midrange than possible with naturally aspirated engines. As a result the engine produces the massive towing power of a truck and the violent acceleration of a race car using low rpm instead of high rpm.

What a total load of crap....I'd like to see some independant testing to confirm their ideas. They just don't make sense

Panda

faster than the speed of sound :

[needturbo6]

Originally Posted by Panda

The intake charge is also increased to a hot temperature to produce more combustion pressure you can't produce compression on the intake cycleand burn faster.

well a hotter gas contains more pressure, so that would mean more compression, wouldnt it?

Originally Posted by Panda

atomised fuel is already above it's flash point. Increasing the termerature further will make it ignite, but why do you want this on the intake cycle?[/COLOR]

more pressure, i assume

just a couple of many incorrect assumptions in your post.

[Psycho Chicken]

Hotter gas only has more pressure if it's enclosed. Hotter intake mixture in the case of an engine would produce lower cylinder fill. The atoms will be further apart, so it would need to have work harder to draw them all into the cylinder. The atoms in cold air are closer together, so you can get more in.

[needturbo6]

Originally Posted by Psycho Chicken

Hotter gas only has more pressure if it's enclosed. Hotter intake mixture in the case of an engine would produce lower cylinder fill. The atoms will be further apart, so it would need to have work harder to draw them all into the cylinder. The atoms in cold air are closer together, so you can get more in.

ahh yes, but maybe this totally different setup doesnt need as much air/fuel to make big power? making it more fuel efficient as the place states. possible...

and the supposed vacumn should draw in the extra atoms..... possible too i suppose.

[MITCHAY]

Hot air expands and cold air contracts. Basic science.

[needturbo6]

Originally Posted by MITCHAY

Hot air expands and cold air contracts. Basic science.

thats the thing, theres a lot more to this "invention" than basic science....

[Mike Gayner]

Originally Posted by needturbo6

ahh yes, but maybe this totally different setup doesnt need as much air/fuel to make big power? making it more fuel efficient as the place states. possible...

and the supposed vacumn should draw in the extra atoms..... possible too i suppose.

What are you drunk? Read it again, the whole point of this bogus crap is that it uses "negative pressure" to draw more air and fuel into the cylinders. Which clearly is not the case, this engine would be incredibly innefficient, especially at higher revs, and I honestly can't imagine getting any gain at all down low.

[Psycho Chicken]

I don't see how the cylinder could have any vacuum to aid cylinder fill, there's only going to be a bee's dick of extra vacuum at TDC, and the downstroke of the piston draws A/F in anyway.

[Gammaboy]

Basically their theory defies a couple of basic rules of thermodynamics.

[mcflux]

Maybe an electric fan supercharger could work with this system ot improve its process?

[Blue Oval Mopar Man]

Originally Posted by davway

well considering that they arent available for ANY ford engines, im taking a stab in the dark and assuming its all aimed at Commo drivers.

HAHAHAHAHA, its probly a ford driver that came up with it just to suck commodoore drivers into using it and getting less power and shyte fuel economy , and have them telling us its actually and advantage !

SWEEEEEETTTT!!!!!!!!!!!!

[Mike Gayner]

I don't know where you got the idea there's no Ford applications, there are Ford motors sitting right there under GM.

[Timmeh]

Originally Posted by Panda

crap, gasses do not have a mass

Incorrect. Gasses DO have a mass and thats the whole principle on why you can leave you inlet valve open past BDC - its called momentum. Basic principle there.

I can appreciate your reply being skeptical, and I can assure you building my high performance turbo engine that I won't even bother reading about this product, but this reply similarly contains false information too.

Tim

[Timmeh]

Sorry to post again but I can't let this go:

Originally Posted by Panda

Where to start, where to start....

[Font=Tahoma]Exhaust Cycle
The Negative Pressure Supercharging process begins with the exhaust cycle. As the exhaust valve opens the massive gas pressure produced after combustion it has already expended it's energy - driving down the pistonforces itself through a compact header with very small and short pipes. This causes the high pressure gas to compress in the small pipe increasing pressure, reducing flow = no net increase in gas flowand accelerate to a high velocity which is twice the speed produced by typical large pipe headersagain, increasing pressure and reducing flow = no net change in gas flow. As a result a negative pressure is produced behind the high velocity gas in the small pipe which is so strong it reduces the pressure in the cylinder during the exhaust stroke. it is the positive pressure in the cylinder which moves the gas, it does not move on it's own

There is nothing wrong with what is said here, although it is described interestingly. The burnt air initially gets pushed out of the cylinder by the piston rising after its power stroke. A set of extractors or well made exhaust manifold will have a low pressure scavenging wave arrive at the overlap from the other pistons that have previously fired, helping draw the air out.

The momentum of the air leaving the cylinder does create a low pressure in the cylinder of a normal engine, but this is where these two designs (the one in topic and a regular engine) differ. At this point in a normal engine, the inlet valve is open (yes, both the inlet and exhaust valves are open at this point, called overlap), and the escaping exhaust burnt mixture leaving creates a low pressure drawing thru the unburnt fuel air mixture of the next cycle. From what I understand with this setup, they are closing the exhaust valve before the inlet valve is opened to have the low pressure trapped inside.

The reason I think this setup is crap is that the inlet valve now has a shorter total time to be open, and may not get the full advantage of the exhaust gas drawing it in.

Originally Posted by Panda

However, the high pressure gas in the small pipe of the header will remain compressed for only a short distance before it builds up back pressure and restricts the gas flow. nopeTherefore, the small pipe of the header is very short and a megaphone pipe is used after the header to allow the compressed gas in the small pipe to gradually expand into the larger diameter of the megaphone pipe.this does actually work - the venturi effect This allows the exhaust gas to flow only away from the exhaust port at a very high velocity and with no back pressure to restrict the gas flow. this part however is crap

Here they are just talking about how to now best get rid of the exhaust gases that have left the engine. However, this part is not as important. Any exhaust gas flowing will leave a low pressure behind, its a basic fundamental of any extractors.

Originally Posted by Panda

Keep in mind that negative (low) pressure is naturally produced behind all moving objects which travel at a high speedcrap, gasses do not have a mass. The faster the speed of a moving object, the lower and stronger the negative pressure is behind the fast moving object. wrong for so many reasonsThe same principle applies to the gas flow in the primary pipe of a typical headerhorse-shit. The smaller the pipe, the faster the gas speed trueand therefore the lower and stronger the negative pressure is behind the gas flow in the header. false

Where you say wrong for so many reasons, I'd like to hear them. I work in aviation and it's what aerodynamics is all about. When a train passes thru a station, the faster it passes thru, the more disturbed the air behind it is, like when you see ads of the train blowing a girls hair as it passes. Just like the faster an aircrafts wing goes, the lower the pressure above it due to the rising airspeed is, and the wing gets sucked up (as well as creating high pressure below it and being pushed up). I don't think what is being said here is wrong, in my opinion. And I still stand that gasses DO have mass, its a basic fundamental on how an engine works, drawing air into the cylinder, as explained in my previous reply.

Originally Posted by Panda

Overlap Period
At the end of the exhaust cycle during the overlap period, the negative (low) pressure is trapped in the combustion chamber by closing the exhaust valve early before TDC and using low exhaust valve lift. so you close in the cylinder while the piston is still compressingSoon after the exhaust valve has closed, the intake valve opens early before TDC still compressingto allow the negative pressure trapped in the combustion chamber to pull the intake charge into the engine instead of into the exhaust system. crap

You seem to be very mixed up here. If the exhaust valve has just closed, you're not on the compression stroke. You're finishing the power stroke, remember that a piston travels twice for every one time it fires. It won't be compressing while either valves are open (in a normal engine, both will be open during an overlap period). Remember the sequence: exhaust (up) - intake (down) - compression (up) - power (down). Your reply there was thinking that this was happening on the compression stroke, but it is clearly describing the exhaust to intake part of the sequence. There is absolutley nothing wrong with the description here - only the theory behind the idea is not what I would use.

Originally Posted by Panda

Intake Cycle
The intake valve opens before TDC and after the exhaust valve has closed, to allow the negative pressure trapped in the combustion chamber to pull the intake charge into the engine and fill the cylinder very rapidly with a greater volume of air early in the intake cycle. still crapThe intake charge is also increased to a hot temperature atomised fuel is already above it's flash point. Increasing the termerature further will make it ignite, but why do you want this on the intake cycle?to produce more combustion pressure you can't produce compression on the intake cycleand burn faster. little bit true

Once again, you have confused the stroke the piston is currently in. No need to explain this again.

Originally Posted by Panda

As the piston moves down the cylinder during the intake stroke, it further reduces the pressure in the cylinder. This pulls an additional volume of hot air into the engine faster than the speed of sound. you're ****ing kidding me aren't youAt the end of the intake cycle the intake valve closes early after BDC same as normalto trap the much larger volume of hot air in the cylinder and prevent the air from being forced back into the intake manifold during the compression stroke. same as normal

I think you're underestimating the speed air flows into a cylinder. Well designed engines will pile air thru the intake port at over 800km/h. So, it's not far off what they quote, but I do agree that 'faster than the speed of sound' is a bit dramatic and exagerated. As you say, the rest is normal, so you've managed to catch up to the right stroke at some time in your thought process.

Originally Posted by Panda

Keep in mind that even though hot gas is less dense it explodes with a much greater force because it reaches its maximum pressure much faster than the more dense cold gas. because it is less dense the computer has to swing the Air / Fuel ratio - giving you less fuelTherefore, the engine is able to produce more power with a hotter intake charge because the increase in power produced by the higher combustion pressure and faster burn of hot gas is much greater than the loss produced by less dense hot air.

The speed at which the fuel burns is important, an uncontrolled burn with hot mixtures will cause detonation and a rapid destruction of the engine. Water injection kits are designed specifically to cool the air fuel mixture, so here is where I am pointing my finger at this idea and calling it crap, rather than trying to correct anomalies in the reply.

I hope that makes things a bit more clear for people, not trying to be a real bass, but there was alot of incorrect information there that needed to be explained.

My verdict: it's crap too.

Tim

[Panda]

Originally Posted by Timmeh

...I can't let this go

I can

Panda

[Casper]

The whole thing can be debunked very quickly. Its based on
A) a cam that creates a "low pressure" senario. Basically, thats how an NORMAL NA engine works anyhow, they are just messing with overlap...no big deal there.
B) That hot gasses explode with more force, which to a degree is correct, HOWEVER, hot gasses also carry far less oxygen...an requirement of any internal combustion engine. So any gain is lost because less oxygen means less fuel can be burnt effectivly.

Basically, if this theory was sound (which it isnt) then every turbo and SC car out there had better remove the intercooler for a free boost in power....not likely.

Its complete rubbish...oh, and the exploding cylinder "test" they did has so many faults its not funny but the real big one is it relies on the same air temp as the explosion would be using the air in the "backyard", try doing it in a vacuum and see what happens.

Don't forget there is a lot of advanced work done on the engine aside from the "supercharger", these mods on there own will improve the performance of the engine, I can't see and "before & after" graphs to indicate the performance gains, I'd be more convinced to see the difference on a dyno before I parted with any bucks.

Regards Prof. Rabbit

Originally Posted by Psycho Chicken

I don't see how the cylinder could have any vacuum to aid cylinder fill, there's only going to be a bee's dick of extra vacuum at TDC, and the downstroke of the piston draws A/F in anyway.