Compressed air "supercharger"? (weird idea)

[Swordsmith]

I was chatting with someone about turbochargers and superchargers this morning (subjects neither of us know much about) and we got to wondering about a weird idea.

What if we added a tank of compressed air somewhere in the intake system, allowing temporary added boost, until the tank ran dry?

I already run around with a tiny compressor (instead of a big heavy spare), and could hook it up to gradually refill the tank using battery power.

I rarely need full boost levels, this would be more of a drag strip thing, where 20 seconds is longer than I'd ever need, so the fact that the tank would only have limited duration, and take some minutes to recharge wouldn't be a problem.


I'm sure there are problems with the idea, maybe even cost prohibitive or even insurmountable ones... but on the surface it sounds like it would be cheap and effective, and oddly similar to installing a nitrous rig, only without the pain of having to keep getting nitrous refills.

 

[River_Rat]

Off the top of my head, even 20 seconds of boost would require a tremendous amount of compressed air. A scuba tank, for example, typically holds around 60 cf of air and it has to be compressed at 3000psi in order to fit it into a tank that size (not small). Your tire compressor simply couldn't be used to store the kind of air we are talking about.

 

[ChrisJ]

You would need to calculate how much volume you could get from the tank above a certain pressure and for how long.

Something tells me even a 50 gallon tank filled to 140PSI couldn't sustain an engine for very long through a 10-20PSI regulator @ 400-500 CFM.

 

[vento]

Why not just use a smaller shot of nitrous? You wouldn't need to use as much and as long as you don't shock the drive train it shouldn't hurt it.

 

[Italianjoe1]

Compressed air won't do anything at all, as it won't pressurize the manifold. A gradual injection into the manifold will just reduce the amount of air coming in via the MAF. A burst of pressure will just explode the plastic manifold.

Adding air alone will not increase any power, you need additional fuel to burn to make power, you add boost to provide extra air to burn the fuel, not the other way around.

 

[Natesriv]

yeah, it won't work...

the impeller blades on the turbo are compressors...they ram more air into the cylinder ALONG with an increase in fuel at the same time (as the gang stated above) to work together to make more power...

Have you guys seen the new engine from some car maker (can't think of the brand) which is both supercharged AND turbo charged!?

 

[cndctrdj]

Boost Films SFL - Add 8 more horsepower to your SOHC with a leaf blower lol [HD] - YouTube

this is a leaf blower.... way more cfm than your air compressor, and it did nothing haha. 8hp was probably because the car was trying to adjust itself and had not yet

 

[ChrisJ]

I'm assuming he realizes you would need more fuel along with the extra air........

 

[severous01]

compressed air will flow backwards out the air filter. it's like electricity, it flows in the easiest direction. all you're going to do is screw up the maf readings

 

[Preloader]

Pipe it to the exhaust manifold...... You could spool up at 700RPM.

 

[ChrisJ]

compressed air will flow backwards out the air filter. it's like electricity, it flows in the easiest direction. all you're going to do is screw up the maf readings

Electricity doesn't flow like air or water.


Sorry, I know, off topic and pointless post but I had to.

 

[SouthFLSonic]

yeah, it won't work...

the impeller blades on the turbo are compressors...they ram more air into the cylinder ALONG with an increase in fuel at the same time (as the gang stated above) to work together to make more power...

Have you guys seen the new engine from some car maker (can't think of the brand) which is both supercharged AND turbo charged!?

Couldn't find anyone new doing twincharging but here is the best example of it.

The car's 1,759.3 cc four-cylinder engine combined supercharging and turbocharging to reduce turbo lag at low engine speeds.[1] Officially, the car produced 480 horsepower (350 kW), but some sources claim that Delta S4 produced about 560 horsepower (417 kW). In 1985, Lancia engineers tested a S4 engine under extreme conditions, reaching 5 bars boost, developing around 1000 horsepower. An engine capacity multiple of 1.4 was applied to forced induction engines by the FIA and the choice of 1,759 cc put the S4 in the under 2,500 cc class, which allowed for a minimum weight of 890 kg (1,962 lb). The combined super/turbocharger system (often referred to as twincharging) was a development of the 037 engine that produced 350 hp (261 kW) with a supercharger only.


VW also used a twincharge until about 3 years ago.

 

[ChrisJ]

I thought either Volkswagen or Volvo had tried to do a combination setup with a turbocharger and a belt driven supercharger.

Who eever it was, realized it wasn't worth the cost and problems.

 

[firstorbit84]

VW had a 1.4 twin charged. I didn't realize they discontinued it.

I saw somewhere a novel engine design where a V8 ran as a 4 cyl and had the other bank of cylinders compress air and act as a supercharger.

 

[ChrisJ]

VW had a 1.4 twin charged. I didn't realize they discontinued it.

I saw somewhere a novel engine design where a V8 ran as a 4 cyl and had the other bank of cylinders compress air and act as a supercharger.

Doesn't seem like it would work? They would be transferring the same exact amount of air the cylinders would N/A, no?

 

[Swordsmith]

Naturally you'd have to add the air somewhere where it would increase the pressure. And of course the entire point would be to allow more fuel to be burned, so figuring out how to synchronize increasing fuel along with increasing air would be necessary.

But Turbochargers and Superchargers do exactly this, they add air pressure and add fuel, allowing more powerful combustion events. So it seems reasonable to expect that the same could be done by adding compressed air.

The key to this idea is that instead of coming up with a way to generate more boost exactly when you need it, and have to carry that equipment around constantly, you instead slowly save up the extra air over a period of time, and then use it rapidly but briefly. Sort of a Christmas Club approach.

A key question though is indeed how much air could really be saved up in a reasonably sized tank, and how long would that air really last in a boost situation.

How long it would take to recharge is a less interesting one; generally speaking, whether you're boosting on onramps or at the drag strip, there's substantial down time between full power runs. I admit that this idea wouldn't really be meaningful in long distance full speed runs, or probably even in tracks where you slow down for turns and want to get back up to full speed for straightaways

Preloader's thought is one that hadn't occurred to me; instead of turning existing 22psi boost into 26 or 30 psi, maybe this would be more useful in eliminating spool up time, so you're at 22psi right away and only have to have enough air saved up to get and keep you there until the turbo takes over.

For the sake of some "back of envelope" calculations, I went to this website and took their consumption figures: operating a 0.8 liter car at 3000 rpm for 60 minutes consumes 72,000 liters of air. Now assuming we have a 1.4 liter car running at 1 atmosphere of boost, or the equivalent of a 2.8 liter car, at an average of 4750 rpm (shifting at 6500 to a higher gear which is at 3000 rpm, and accelerating again each time) for 15 seconds (for a not spectacular Sonic 1/4th mile) that means we're looking at 1662.5 liters of air consumed in a run. A ten liter tank pressurized at 150 psi would contain 1500 liters of air. So we aren't in "out of the question" land here.

Here's a 5 gallon tank from Harbor Freight for $20, so this isn't an inherently expensive idea...

I get that it's all still a pie in the sky crazy idea I'll probably never even attempt... but thus far it doesn't seem impossible.

 

[River_Rat]

You need to check your maths. Ain't no way that you're fitting 1500 liters of air in a 10 liter tank at 150 psi.

 

[ChrisJ]

Naturally you'd have to add the air somewhere where it would increase the pressure. And of course the entire point would be to allow more fuel to be burned, so figuring out how to synchronize increasing fuel along with increasing air would be necessary.

But Turbochargers and Superchargers do exactly this, they add air pressure and add fuel, allowing more powerful combustion events. So it seems reasonable to expect that the same could be done by adding compressed air.

The key to this idea is that instead of coming up with a way to generate more boost exactly when you need it, and have to carry that equipment around constantly, you instead slowly save up the extra air over a period of time, and then use it rapidly but briefly. Sort of a Christmas Club approach.

A key question though is indeed how much air could really be saved up in a reasonably sized tank, and how long would that air really last in a boost situation.

How long it would take to recharge is a less interesting one; generally speaking, whether you're boosting on onramps or at the drag strip, there's substantial down time between full power runs. I admit that this idea wouldn't really be meaningful in long distance full speed runs, or probably even in tracks where you slow down for turns and want to get back up to full speed for straightaways

Preloader's thought is one that hadn't occurred to me; instead of turning existing 22psi boost into 26 or 30 psi, maybe this would be more useful in eliminating spool up time, so you're at 22psi right away and only have to have enough air saved up to get and keep you there until the turbo takes over.

For the sake of some "back of envelope" calculations, I went to this website and took their consumption figures: operating a 0.8 liter car at 3000 rpm for 60 minutes consumes 72,000 liters of air. Now assuming we have a 1.4 liter car running at 1 atmosphere of boost, or the equivalent of a 2.8 liter car, at an average of 4750 rpm (shifting at 6500 to a higher gear which is at 3000 rpm, and accelerating again each time) for 15 seconds (for a not spectacular Sonic 1/4th mile) that means we're looking at 1662.5 liters of air consumed in a run. A ten liter tank pressurized at 150 psi would contain 1500 liters of air. So we aren't in "out of the question" land here.

Here's a 5 gallon tank from Harbor Freight for $20, so this isn't an inherently expensive idea...

I get that it's all still a pie in the sky crazy idea I'll probably never even attempt... but thus far it doesn't seem impossible.

Google how much volume is in a size 80 scuba tank @ 3000PSI and its size and then look at what you said.

 

[Swordsmith]

Very likely the math is wrong. I just saw 150 times 10 and got 1500... but PSI and liters don't actually match up. Lets get out of metric, to start with, 1662 liters is 58 cubic feet. So I need to store lets say 60 cubic feet, fitting that into a five cubic foot tank would mean I'd need to be at 12 atmospheres, or 176psi. That still doesn't seem improbably large or improbably high pressure, I've got a 200 PSI tank out in my workshop.

How about the delivery, though, to deliver all 58 cubic feet in 14 seconds I'd have to be doing so at a rate of 4.14 cubic feet per second or 248 CFM. That looks like a lot bigger problem. Typical compressor output is 4CFM... on the other hand that's coming down a 1/4inch hose. How about a 1 inch ID pipe, or even larger... let that air out of the pressurized tank fast?

Also, this is assuming we need to add one extra atmosphere for a full 14 seconds, while I think there would be advantages to adding even part of that, and for even shorter spans of time.

 

[River_Rat]

Again, 5 cf is 37 gallons. You could potentially lug that around, and it might hold enough air, but that is teetering on the edge of impractical.

Putting that aside for the moment, I'm trying to work this out. I imagine you are thinking of piping the air in to the intake before the turbo (because if you were to do it after, you would likely stall your compressor, no?). Your system is going to have to be contained in some way so that your charge of compressed air does not find its way out the intake. Some type of check-valve might do the trick. Even then, I'm afraid that 250 cfm is going to be less flow than your engine already needs. According to this calculator, even 350 cfm is only going to yield about 225 crank hp. So you're gonna need an even bigger tank if you want to increase flow (and power) above conventionally achievable levels.

It's a neat idea, but I really think that storage capacity is a serious limitation (and just think of the weight of the tank and compressor).

Seems to me that a much more prudent alternative would be to get an oversized turbo and feed it with a small bottle of N20 for spooling purposes only.