14 replies to this topic

[mariner]

A very different way of supercharging, who needs the earth's atmosphere?

 

 

 

 

It is nice to see that eh NHRA signed this off - F1 please note!

[desmo]

Compressed air supercharging makes perfect sense for drag racing. Probably more sense than an on-board mechanical compressor. I'd think using unnaturally oxygenated "air" might make it even better.

[Greg Locock]

I knew someone who used pure oxygen to supercharge his motorbike. It did not end well apparently. He also used to drive a Model T around Los Angeles. Great guy 

[gruntguru]

Interesting that this system doesn't draw air from the atmosphere during boosted operation. Less compressed air would be required if the energy wasted during expansion to the final pressure of 32 psig, was utilised.

 

Funny that the owner referred to the discharge point as an "ejector" which is of course a device which would use compressed air to draw-in and compress atmospheric air.

[GregThomas]

Hmm, as a roadrace motorcycle builder I can't help thinking about using a spine frame main tube as an air reservoir. Button on the bars for a shot of air - and open another fuel feed...

 

Use it in short bursts like the "alleged" concealed battery assist on racing pedal cycles

[mariner]

I've mentioned it here before but way back in 1960's GM research developed an "ejector" air supercharger system using an "off the shelf" belt driven compressor to a storage tank with an output line to a pre carb. venturi..

 

On kickdown the compressed air was shot into the middle of teh ejector venturi to accelerte the incoming atmospheric air. 

  

It worked but the inabilty to get frequent boosts due to the   long compression time made it ineffective - so they got out the old boring bar instead.

 

A system with a belt drive from a free wheeling pulley on the prop shaft with a throttle closed signal could have been air pressure regen ?

[Magoo]

I've mentioned it here before but way back in 1960's GM research developed an "ejector" air supercharger system using an "off the shelf" belt driven compressor to a storage tank with an output line to a pre carb. venturi..

 

On kickdown the compressed air was shot into the middle of teh ejector venturi to accelerte the incoming atmospheric air. 

  

It worked but the inabilty to get frequent boosts due to the   long compression time made it ineffective - so they got out the old boring bar instead.

 

A system with a belt drive from a free wheeling pulley on the prop shaft with a throttle closed signal could have been air pressure regen ?

 

 

Fascinating system. I have the materials somewhere, will have to dig them up. 

 

The assumption was the engine would have a ready supply of compressed air from the airbag suspension system introduced by GM in 1958. When it proved to be a disaster, the venturi supercharger died too. 

[PJGD]

A modern, or at least scientifically updated version of this concept was covered in SAE paper 2008-01-0299 "Fluid-Dynamic Supercharger" by John Vetrovec of Aqwest, LLC.

 

A boost ratio of 1.8:1 is claimed, and functional efficiency is enhanced with deceleration energy recovery and a variable area venturi.

[mariner]

Those papers would make interesting reading. I wonder if anybody ever thought of using it on a truck as they have lots of space and already have a big air compressor for the brakes?

[Lee Nicolle]

Seems sensible for drag racing. Not much good for anything else. 

Turbos screw up the exhausts, Superchargers at best have belt issues and the weight behind the centreline of the car is better as well. And all those turbos and blowers are heavy and eat space. And power.Though again this is nothing new just a modern take on an old idea.

[ddoubledd]

Compressed air supercharging makes perfect sense for drag racing. Probably more sense than an on-board mechanical compressor. I'd think using unnaturally oxygenated "air" might make it even better.

 

Unnaturally oxygenated "air", like Nitrous Oxide?

 

 

I knew someone who used pure oxygen to supercharge his motorbike. It did not end well apparently. He also used to drive a Model T around Los Angeles. Great guy 

 

Oops, he must've overlooked that combustion heat expands the N2. And if petrol is the fuel, insufficient fuel for the O2 present will result in detonation. 

 

 

Interesting that this system doesn't draw air from the atmosphere during boosted operation. Less compressed air would be required if the energy wasted during expansion to the final pressure of 32 psig, was utilised.

 

Funny that the owner referred to the discharge point as an "ejector" which is of course a device which would use compressed air to draw-in and compress atmospheric air.

 

I can't think of a way to draw air from a lower pressure to a higher pressure. I don't think any energy was lost by the expansion of air volume from the tanks to intake manifold. I think that is an isometric conversion which always follows the conservation of energy. As the mass of gas (air) is given a much larger volume, pressure decreases so temperature also decreases. But the result must keep the total energy of the gas constant because no work was done. I first thought the work to move the air into engine cylinders should be considered, but it falls in the negligible pile. The final pressure from the system is not 32 psi but rather 46.7 psi, because the system is isolated from the atmosphere. Enthalpy is reduced in the storage tanks as heat is leaked to the atmosphere after compression. But because gas density remains constant, the loss of heat can only affect pressure and temperature. The combustion process only needs air mass with sufficient O2 to match the fuel, and N2 to expand; it does not use the total energy of the gas. A turbine, or any airfoil would, because the these devices convert air velocity to mechanical work, and static enthalpy increases how much work can be converted for a given velocity. In the ICE intake, the lower static energy should actually increase the mass of air filling cylinders, when air velocity returns to zero. Because the dynamic velocity is much lower (same mass but less volume to move), all the bends in the air path have much less drag and turbulence effects. 

 

Years ago, hmm maybe decades, I designed a similar system for street cars. A typical car may show off from a stoplight, need power for an entrance ramp, or for passing. These are all very short in time duration, and a 1000 HP street engine would definitely be impressive. That 10 seconds of fun would have required 10 minutes to refill the tanks. 

 

I can tell what works really well by going to the drag strip where they go quickest for the least possible money. 15 year ago everyone there had an LS-X engine pulled from salvage, stuffed into any car they had. You can put any number as the suffix, it doesn't really matter that much. All original parts in the block. They increased the ring gaps, but then reassembled with the old rings, old bearings, even old gaskets. Most had over 150k miles. They stacked two 150HP shot N2O injectors in the intake. They hit the first just after launch, the next at 5k RPM after the shift to 2nd. Everyone called them LSX Bombs. But everyone learned, they were not blowing up. Probably 60 cars out there every weekend, just banging them. This went on for years and years. Sure there were failures, but always for other reasons than would be assumed. 

 

You needed that history for this bit. The turbos started showing up and soon the nitrous cars were loosing. They were the $150 turbos bought from AliBaba. Makeshift airboxes, injectors, based only on whatever they saw on youtube. There was definitely a learning curve. But today, everyone has a giant turbo and E85 in the tank. The used LS engines are still holding up just fine at over 1000 HP. No blowers, no nitrous, no billet engines, no ARP fasteners, definitely OEM original parts. And get this, almost everyone drives their car home. 

 

 

Seems sensible for drag racing. Not much good for anything else. 

Turbos screw up the exhausts, Superchargers at best have belt issues and the weight behind the centreline of the car is better as well. And all those turbos and blowers are heavy and eat space. And power.Though again this is nothing new just a modern take on an old idea.

 

 

I've never met a heavy turbo, blowers weigh a bit more but one girl can carry it across the shop. Yes, blowers are engine driven, and the drive load limits net shaft power, and adds to crankshaft complications. But turbos present very little load to the engine. Exhaust gases almost entirely exit the cylinder due to a massive pressure differential. When the valve opens, cylinder pressure may be around 1500psi, about 100:1 over atmosphere. Ignoring some minor turbulence and drag, more than 90% of if leaves the cylinder before the piston can start to help push it out. This gas is hot, in a large pressure wave, moving at a high velocity. We put a turbine in its path to convert all that into mechanical power. Turbines are really a bunch of airfoils to get the most mechanical energy with the least drag, the same way wings work. It's really a beautiful thing, The engine didn't have to impart much work to move this gas, all it really did was open the valve. This energy is normally dumped, but here we have a good tool to capture. 

 

These are the reasons turbo systems dominate others. The CAS system has only the intake charge temperature advantage over turbos. To capture this advantage, you'd have to increase compression ratio a lot. 

[Greg Locock]

No, oxygen plus hot metal. Also known as a thermic lance

[gruntguru]

Oops, he must've overlooked that combustion heat expands the N2. And if petrol is the fuel, insufficient fuel for the O2 present will result in detonation. 

Not necessarily. Even if you tune the mixture correctly, the addition of significant amounts of pure oxygen results in high combustion temperature and detonation. (This was known before WW2 when Nitrous was selected for chemically supercharging aircraft)

 

I can't think of a way to draw air from a lower pressure to a higher pressure.

As I said - it's called an "ejector". Try Google. 

 

I don't think any energy was lost by the expansion of air volume from the tanks to intake manifold. I think that is an isometric conversion which always follows the conservation of energy. As the mass of gas (air) is given a much larger volume, pressure decreases so temperature also decreases. But the result must keep the total energy of the gas constant because no work was done.

OK, energy is not "lost". "Wasted" or "lost opportunity" is more correct. The process they are using is adiabatic whereas using an ejector, the compressed air does some useful work during expansion. This closer to the ideal "isentropic" process where the compressed air is expanded to the final pressure - doing some useful work during that process, and al;so resulting in a lower final temperature than adiabatic expansion. Note the temperature at the ejector discharge will not be this low because the cold expanded air is mixed with compressed atmospheric air. Colder charge may be the reason for going the non-ejector route.

 

The final pressure from the system is not 32 psi but rather 46.7 psi, because the system is isolated from the atmosphere.

The final pressure is 32 psi. 32 psig to be precise. 46.7 psia if you prefer. Isolation from the atmosphere has no bearing on whether pressure should be recorded in gauge or absolute. 

 

These are the reasons turbo systems dominate others. The CAS system has only the intake charge temperature advantage over turbos. To capture this advantage, you'd have to increase compression ratio a lot.

Or just increase charge pressure.

Edited by gruntguru, 22 August 2023 - 23:48.

[Lee Nicolle]

Unnaturally oxygenated "air", like Nitrous Oxide?

 

 

 

Oops, he must've overlooked that combustion heat expands the N2. And if petrol is the fuel, insufficient fuel for the O2 present will result in detonation. 

 

 

 

I can't think of a way to draw air from a lower pressure to a higher pressure. I don't think any energy was lost by the expansion of air volume from the tanks to intake manifold. I think that is an isometric conversion which always follows the conservation of energy. As the mass of gas (air) is given a much larger volume, pressure decreases so temperature also decreases. But the result must keep the total energy of the gas constant because no work was done. I first thought the work to move the air into engine cylinders should be considered, but it falls in the negligible pile. The final pressure from the system is not 32 psi but rather 46.7 psi, because the system is isolated from the atmosphere. Enthalpy is reduced in the storage tanks as heat is leaked to the atmosphere after compression. But because gas density remains constant, the loss of heat can only affect pressure and temperature. The combustion process only needs air mass with sufficient O2 to match the fuel, and N2 to expand; it does not use the total energy of the gas. A turbine, or any airfoil would, because the these devices convert air velocity to mechanical work, and static enthalpy increases how much work can be converted for a given velocity. In the ICE intake, the lower static energy should actually increase the mass of air filling cylinders, when air velocity returns to zero. Because the dynamic velocity is much lower (same mass but less volume to move), all the bends in the air path have much less drag and turbulence effects. 

 

Years ago, hmm maybe decades, I designed a similar system for street cars. A typical car may show off from a stoplight, need power for an entrance ramp, or for passing. These are all very short in time duration, and a 1000 HP street engine would definitely be impressive. That 10 seconds of fun would have required 10 minutes to refill the tanks. 

 

I can tell what works really well by going to the drag strip where they go quickest for the least possible money. 15 year ago everyone there had an LS-X engine pulled from salvage, stuffed into any car they had. You can put any number as the suffix, it doesn't really matter that much. All original parts in the block. They increased the ring gaps, but then reassembled with the old rings, old bearings, even old gaskets. Most had over 150k miles. They stacked two 150HP shot N2O injectors in the intake. They hit the first just after launch, the next at 5k RPM after the shift to 2nd. Everyone called them LSX Bombs. But everyone learned, they were not blowing up. Probably 60 cars out there every weekend, just banging them. This went on for years and years. Sure there were failures, but always for other reasons than would be assumed. 

 

You needed that history for this bit. The turbos started showing up and soon the nitrous cars were loosing. They were the $150 turbos bought from AliBaba. Makeshift airboxes, injectors, based only on whatever they saw on youtube. There was definitely a learning curve. But today, everyone has a giant turbo and E85 in the tank. The used LS engines are still holding up just fine at over 1000 HP. No blowers, no nitrous, no billet engines, no ARP fasteners, definitely OEM original parts. And get this, almost everyone drives their car home. 

 

 

 

 

I've never met a heavy turbo, blowers weigh a bit more but one girl can carry it across the shop. Yes, blowers are engine driven, and the drive load limits net shaft power, and adds to crankshaft complications. But turbos present very little load to the engine. Exhaust gases almost entirely exit the cylinder due to a massive pressure differential. When the valve opens, cylinder pressure may be around 1500psi, about 100:1 over atmosphere. Ignoring some minor turbulence and drag, more than 90% of if leaves the cylinder before the piston can start to help push it out. This gas is hot, in a large pressure wave, moving at a high velocity. We put a turbine in its path to convert all that into mechanical power. Turbines are really a bunch of airfoils to get the most mechanical energy with the least drag, the same way wings work. It's really a beautiful thing, The engine didn't have to impart much work to move this gas, all it really did was open the valve. This energy is normally dumped, but here we have a good tool to capture. 

 

These are the reasons turbo systems dominate others. The CAS system has only the intake charge temperature advantage over turbos. To capture this advantage, you'd have to increase compression ratio a lot. 

Turbos restrict exhausts, end of story. And the big ones are quite heavy, more so multiplied by two plus all the headers, intercoolers etc etc.

A 6/71 is decidedly heavy. I once picked one up, and all very top heavy.

ALL supercharging creates a LOT of intake heat unless on methanol, and even then a LOT hotter than n/a

[GreenMachine]

Turbos restrict exhausts, end of story. And the big ones are quite heavy, more so multiplied by two plus all the headers, intercoolers etc etc.

A 6/71 is decidedly heavy. I once picked one up, and all very top heavy.

ALL supercharging creates a LOT of intake heat unless on methanol, and even then much hotter than a turbo and a LOT hotter than n/a

 

FTFY. 

 

The fuel won't alter the basic physics, compress a gas and it creates heat.  Methanol won't help unless injected upstream of the inlet, where (some of?) the heat is absorbed vaporising the methanol and the charge entering the chamber is much cooler than leaving the blower, even without intercooling.

Edited by GreenMachine, 24 August 2023 - 08:30.