Air Tank Boosting for Dire Traffic Situations

[BretCahill]

I can usually find my "new" ideas in minutes and they are often decades old. This might be an exception:

Eliminate turbo lag and shaft driven superchargers with something much more useful to most commuters: a two to 5 second burst of air from a pressure vessel that would help scoot any under powered vehicle across a busy intersection and into traffic.

For, say, a 2 l engine an 8 gallon air tank would hold 8 cubic feet STP at 120 psi or 13 ft^3 at 200 psi. This should be more than enough boost air for drivers waiting at intersections running at low initial rpm. Since this system wouldn't be used to burn rubber at every stop light a small compressor would recharge between "situations." You stomp the gas, solenoids open and you have power the once or twice a day -- or month -- you need it.

The advantages over turbo and super charging are many obvious:

No power is sapped from the crank shaft and no back pressure -- assuming the tank system wasn't combined with turbo charging to over come turbo lag.

The intercooler effect would be enormous, delivering sub ambient temperature air. The air might even require some warming.

A venturi [jet pump] or some other means could use the energy from the expanging air to suck in outside air for a smaller tank or lower pressure or longer boost time or all three.

The boost pressure could be higher without damaging the engine because it would only last a few seconds.

The boost pressure could be easily adjusted any time with the air regulator.

The system is cheap, simple and off the shelf.

Unlike a supercharger, the tank could be located anywhere space isn't critical.


Bret Cahill

 

[swall]

If you are going to all the trouble of mounting a compressed gas tank, hoses, solenoids and a regulator,you might as well go directly to nitrous.

 

[firefrog]

Hey
Good ideas. Been thinking about this myself. Safer, easier and cheaper than nitrous. Don't need special hardware. My concern is whether a regular MAP sensor has the range from vacuum to boost to control fuel delivery. I'm wondering if a regular propane setup could handle this. I think you'd still need timing retard when the air kicks in. You could hook up a vacuum motor to control a flapper to prevent the air from spitting out the front. I was wondering about a light fibreglass air tank (how dangerous would an 'air pack tank' be?). What kind of pressure does a smog air pump put out? Could that be used to refill the tank? Can you unload the air pump when not needed? So many questions. Are you really gonna try to build this? I'd like to try too.

 

[SBBlue]

It's not hard to do the math folks. You're brainstorm pencils out like this:

Assuming a 5 liter engine @ 3600 rpm:

Volume of intake air per second, throttle wide open: 150 liters, or 39.6 gallons.

Vol of air @ atmospheric pressure in a 5 gal tank @ 200 psi: 68 gallons.

Time to use up all the air with the throttle wide open: 1.7 seconds

 

[sprintcar]

Add to SBBlue's math - the fact that the fuel system has to react properly in an already lean burn engine condition, as well as upsetting the moving column of intake air - could put you in the middle of the intersection when it chokes....

If it's an automatic, just 'brake torque' so you're further into the power band. Stick shift ...well, you get the picture -



Keep the wheels on the ground
Bob
showshine@aol.com

 

[magnograil]

SSB - They are talking underpowered vehicles. Unless, of course, your 5L is a dodge. Still, at half or quarter the displacement the same holds true. Enough to get you into the intersection before the power dies. People already have problems figuring out which is the throttle and which is the brake pedal. Imagine a throttle pedal that reacted differently each time. I would only agree to it if they took out the airbag and seat belts and put a spike in the steering wheel so people that end up rear-ending others would be taken out of the gene pool.

 

[ruggedscot]

How would you stop the air getting out of the intake ?

If you try to put air into the engine it may escape through the main intake as there would be no real stop to prevent that from happening ?

Reed valves or the like ?

Still think that we would be struggling to have enough air on tap to do any good.

Rugged

 

[BretCahill]

A turbo charger manfacturer said air tank boosting would be the same as nitrous -- the original idea was to be used along with turbochargers to eliminate turbo lag.

Then I considered that the only time I really need to move fast is scooting across a busy intersection which takes two - 5 seconds. By the time the turbo spools you don't really need it. Why not forget the turbo altogether and keep the tanks.

Before the Chinese started dumping other cheap consumer and industrial products on the market, it might be reasonable to use nitrous.

But now it would be more convenient and probably cheaper to just buy a solenoid, a swing check valve, a regulator, a tank and some 1/2" to 5/8" tubing. And a compressor.

A fuel injection system designed for a supercharger could be tricked into thinking a supercharger was delivering the air.


Bret Cahill

 

[richdubbya]

Depending on the length of the tubing, it would seem to me that a larger diameter would be needed to move that much air in 5 sec., especially as the pressure drops. It seems to me that the fuel regulation would be difficult, at low rpm the pressure leaving the system would be 200psi with few intake cycles, approx 2.5 sec later it would be 100psi at a much higher rpm. I believe that all the issues could be worked out, but it will be a fairly complicated system. How about a short intake tube welded to the manifold, a small side draft carb that will work with a blow thru supercharger, the idle circuits blocked, the compressed air delivered to a small plenum before the carb? the carburetor should adjust for the actual airflow. you would have to be sure gas fumes could not enter the air tank. One advantage to this system over a blower/turbo is that the air will be cooled by the decrese in pressure rather than be heated by compressing.

 

[BretCahill]

These ballpark calculations are for a 2 l engine. This will work for larger engines but the air pressure or the tank size and tubing size will need to be increased accordingly.

The 1/2" tubing would run from the 8 gallon 100 psi tank -- 8 cu ft of air at STP -- to the regulator under the hood. Since air has little mass little expansion pressure drop energy would be required to get the velocity of the air up to even sonic speeds and we can assume the pressure in the tubing is close to 100 psi and the tubing only needs to move about 1 cu ft of volume.

The cross sectional area of a 1/2" tube is ~ 0.2 sq in. = 0.0014 sq ft.

Assuming turbulent plug flow with a uniform velocity profile, the velocity in the tube for a 4 second discharge would, therefore, be:

(1 cu ft/4 seconds)/ 0.0014 sq ft = 180 ft/sec.

This seems reasonable considering air escaping a bicycle tire or shop nozzle reaches sonic speeds. Fanning friction pressure drop can be determined if anyone still thinks that would be significant but the regulator is going to expand the air all the way down to 10 - 15 psi anyway. A large pressure drop in the tubing might even be desirable in sourcing a cheaper regulator.

A venturi spliced in the line could operate like a jet pump and suck in even more air for a smaller tank or longer boost times or a larger engine.

For fuel injected vehicles, it would be trivial to trick the injection control system into thinking it was a supercharger.

The most important advantage, other than it's simplicity, is that this system doesn't suck any power from the crankshaft like a supercharger and it doesn't take several seconds to get going like a turbo and you don't have to deal with bottled gas like nitrous. Either after market or stock it would always be good to go.

And if you had a flat tire, you could always pump it up in seconds.


Bret Cahill

 

[GregLocock]

I think the idea has merit. I would be very interested in an accurate predicition of the temperature of the air as it comes out of the expansion nozzle. A short term booster like this may have enough thermal inertia to get around that problem, unlike the infamous air car.





Cheers

Greg Locock

 

[GregLocock]

Also bear in mind that Mach choking of the nozzle will limit your expansion ratio

Cheers

Greg Locock

 

[1Bluegrass]

I just saw a mag advertisement on just such a bottle compressed unit supplying a turbo.

 

[BretCahill]

Fluid mechanics calculators are fun to play around with to get some numbers. Google "Reynolds Numbers" for something like:

http://www.efunda.com/formulae/smc_fluids/calc_pipe_friction.cfm#calc

and check my numbers:

0.018 cP viscosity for air @ 70 degrees F
114.7 psi abs pressure at tank
velocity = 180 ft/sec
tubing dia. = 0.5"
length = 20 feet
density = 9.4 kg/m^3 @ 114.7 psi.

As you try out lower and lower tank pressures / densities you'll see the output pressure from a 1/2 or 5/8" line does indeed drop but it isn't prohibitive.


Bret Cahill

 

[BretCahill]

United States Patent 4,162,281
Ingraham July 24, 1979

--------------------------------------------------------------------------------
Carburetor fuel atomization apparatus


Abstract
Apparatus for feeding compressed air to an automobile carburetor including a compressor, a compressed air holding tank, an electric air regulator control switch, a manually operated air regulator valve, a solenoid controlled flow valve, tee connections to idler jets, a cylinder and an air line connecting all of the aforesaid devices in sequence. The cylinder has a piston therein connected to a lever plate mounted on the throttle valve shaft in the cylinder of the automobile. The lever plate is connected by linkage to the accelerator pedal of the automobile.

~~~~~~~~~~~~~~~~~~~

They have dozens of hits on

http://www.uspto.gov.

The question is why didn't the boost tank idea catch on?

Maybe less traffic made scooting across intersections less of a problem than today, and now that the patents have expired, there isn't much economic incentive to push for it?

Maybe when fuel costs weren't considered a factor performance vehicle owners were thinking all power all the time?

Maybe it was considered gauche to stick a compressor or tank into a vehicle with wings?


Bret Cahill

 

[magnograil]

Without some sort of one way valve, as soon as the air supplied by the tank increases manifold pressure above ambient, the flow will be out the air duct. Most fuel injection systems can handle the rise in pressure (or lack of pressure drop) in the intake since they measure the manifold pressure (except, of course, dodge). At wide open throttle (without a check valve) all you can do is eliminate the pressure drop which is only a couple PSI. Plus, you have to drag all that extra weight around for occasional use. Try turning off the air conditioner instead.
Regardless, according to your calculations you have 180 FPS air through a 0.5" diameter line which gives a dynamic pressure of 0.002378*V^2/2 = 38.5 PSF. Sea level air pressure is 2116 PSF. So you managed to increase the pressure by 1.8%. Even a small supercharger can put out 8 PSI (1152 PSF). Maybe you should just put in a valve to bypass the air filter?
You will find lots of wild ideas "patented". Most do not work. The patent office does not have a clue what works and what does not. For instance, "curved connecting rods that will stretch at high RPM to increase compression ratio and power". Completely disregarding the fact that the same rods will bend under combustion loads allowing the gas to expand without doing work on the crank (that is if they do not break first).

 

[Rob45]

How about using that compressed air to boost the speed of, reduce the time required to spool up a turbocharger?

 

[GregLocock]

I think that's probably where this idea started out in the past. You get much more bang for your very limited buck by heating the air before it hits the turbine, so injection before the combustion chamber seems sensible.

After all, the additional delay is only of the order of one cycle of the engine, the difference in energy available from the injected air is a factor of three or so.




Cheers

Greg Locock

 

[ivymike]

For instance, "curved connecting rods that will stretch at high RPM to increase compression ratio and power".

hahaha... that's a good one... there's a better one out there though - I once stumbled upon curved connecting rods that "redirect the force application to the crankshaft to increase torque" - apparently the guy thought that if you bent the rods, the (kinematic) force would be applied at a different angle, resulting in torque at TDC, etc.

 

[Lou Scannon]

I have heard of cases where engines have engaged in the self-preservation tactic of bending their connecting rods due to the extreme forces of detonation, thereby lowering their compression ratio and abating the detonation!