I've discovered that most of my air tools don't necessarily need high pressure, but instead, high airflow (CFM).

So I was thinking, looking around the garage, and came up with what is probably a ridiculous idea, but I was curious what you guys might think. Obviously, this is not well thought out and merely just a basic idea.

Removing the exhaust rockers, and tying the spark plug holes together, feeding a large air tank, with that engine driven by a large electric motor with a small pulley on the motor, and a larger pulley on the crankshaft.

A typical starter might have 1.5 HP, with 15 teeth, and a flywheel might have about 150 teeth, for a 10:1 ratio. Use a 5hp single phase motor and I could change that ratio to 3.3:1 or thereabouts. That's a 4" pulley on the motor, and a 10" pulley on the crank.

The math should be something like this, using a 2L import engine of some kind:
CFM = ((CID * RPM) / 1728 ) * (drive pulley diameter / comp pulley diameter)
CFM = ((122cid * 3540rpm) / 1728) * (4" / 10")
CFM = 250ish * 0.4
CFM = 100cfm

Considering cylinder pressures of an engine in reasonable shape would be in the 120-150psi range...

Acquiring and modifying pulley's is easy. Mounting an electric motor is also easy.

Hmmmmm. What do you guys think? Imagine having four friends over, all using air tools, and never running out of air. This appealed to me because I have a 4 cyl 2.0L honda engine sitting in the corner I'll never use, and I'm sure I could find or dig up a nearly free 5HP single phase Baldor...

 

I think its been done, and I believe it took a lot more than a 5hp motor. Good idea though.


Stryder

 

A high efficiency electrically powered commercial air compressor delivers about 3.6 CFM per "true" horsepower.

If you want to get 100 CFM out of your arrangement it is going to take at least 27 horsepower to do it. Your 5 horsepower motor is not going to be enough to spin the engine at that speed against that kind of load. You're asing to repeal the laws of physics.

The underlying idea is OK. A common implementation is to use half the engine's cylinders to develop power (on gasoline) and the other half to compress air. It used to be possible to buy kits to convert your Ford flathead V8 to portable air compressor duty in this manner. It works, and a large volume of air is generated, but the resulting air is hot and contaminated with oil and crankcase blowby. It is also woefully inefficient, considering the amount of gasoline it uses for the amount of air produced.

 

Most of the gasoline powered construction compressors use a Ford 302, one side running normal, the other with a special head to compress air. Most of those are 100cfm.
I'm doing something similar with a Subaru engine to run about 25cfm.

 

I've been thinking about this as well. From years of reading about on-board air compressors converted from AC pumps in 4 wheel mags. I thought, why not plumb the compressed air back into the engine to make it run, thus perpetuating the engine to power the pump again and again. I thought "what a crazy idea", until I discovered it on the internet. Right now a French car is doing just that....runs on air, no gasoline. Anyhow, considering that the AC pump is a tried and true way of making compressed air, what if you mounted (with custom brackets) 4 AC pumps to the same motor? only the water pump and alternator need to stay on. With 4 pumps, you're getting 4 times the air. Either plumb it into 4 seperate tanks/outlets for 4 different users, or plumb all 4 into one big outlet for 4 times the air output. I know it's my Norwegian thinking, but don't it make sense?

 

Great feedback guys, thank you. Lots of neat ideas here. I was trying to stay away from gasoline because gas is always getting more expensive, and since it's mounting in a closet in my garage, gasoline obviously is a bad idea. That's why I thought maybe I could turn a small gasoline engine with an electric motor, since I have both lying around.

I have a two cylinder lawnmower engine with a cracked head... maybe I'll try that first since it's smaller, replace the head with a plate of aluminum or steel, and use two check valves. One for air in, one for air out.

 

every "invention" starts with a little R and D.

 

and a few fires!

 

If that's the case, I must be on track to pass up Edison

 

"A car that runs on air, no gasoline".

Come on guys, that's perpetual motion. It violates the first law of thermodynamics (conservation of energy). No such animal.

It is possible to create engines which charge up an air tank through a compressor, then use the air tank to start the engine later instead of a battery and starter. (Some experimental aviation diesels do this). But this isn't going to work without energy input from an outside source (fuel).

"Hook 4 air pumps to one motor and get 4 times the air?"

Sure. This works. But you place 4 times the load on the motor. No free lunch here;
the ratio of CFM to horsepower doesn't change.

"Invention starts with R&D?"

Sure. But we might as well read some books, and stand on the shoulders of Newcomen and Watt and Newton and Maxwell rather than re-discover what people learned 300 years ago.

 

Well said fefarms! I might add that many industrial diesel engines and some over the road trucks start with air starters. Very common inthe oilfields.

 

Grimmer Schmidt made compressors like that. Neat idea, portability with a lot of cfm.

 

make note everything I was saying was tongue-in-cheek, but here's a link to the air car from France. http://www.theaircar.com/howitworks.html And the 4 pumps, vs. 1 is minimally 5-10 hp difference. 1 pump is the normal ac pump, 1 pump would be the power steering pump, 1 pump would be the thermactor air pump, and 1 pump would be the extra 5-10 hp drain. so an engine normally runs 4 pumps( 4th being the water pump) and an alternator. So with an engine running stationary, and not typically needing power steering, therm., and Ac, yet these are converted, there's no significant difference between running 4 AC converted pumps, compared to what's in a truck or car. Just 1 added on pump....or just run 3, but he wanted 4, so... Anyway, that was my Norwegian thinking. Have fun.

PS: with a "little" R and D...you know, a little engine to start with? My bad there, I put the quotations around the wrong word.
PSS: on a serious note, nothing will beat a 2 stage electric compressor dollar-for-dollar.

 

If I wanted to run this on gasoline, I'd simply make an adaptor to attach the back of the honda engine to the snout of the rover v8 engine and use the rover as an air compressor

Since gasoline in a closet is a bad idea (I have a tendency to catch on fire just thinking about such things) I was thinking of using "things lying around" to form a combination of "stuff" that provides a lot of CFM without much, if any, cost. I already have a 60 gallon air tank which has multiple size fittings, including two fittings that are 2" in diameter. Great for an intake, and exhaust of something that produces crazy CFM.

Air conditioning compressors are used by off-road guys to run air tools as well as inflate tires after a day in the mud/dirt/brush, but I ruled them out right away only because I don't have a shelf of them.

Might any of you know of suitable math formulas for calculating what HP is required to turn a crank, piston, rings within a bore, based on measurements? That might offer me some clues as to calculating what might work with what. Dispite my broken foot, I dug out of the attic a 5HP 220V baldor motor I can use for this, so I don't think that will turn a rover V8. At least not while compressing air. Maybe with the heads off it would spin it just fine.

Maybe when my foot heels, I'll try that just to see what happens. It's not like I have anything to put the rover v8 into at the moment.

 

Go here frederic. http://www.aircompeq.com/formulas.html
It may have what you are looking for. FYI, a 5HP electric motor would struggle turning a V8 engine of appx. 5 Litre displacement at anything over 100 RPM. The parasitic losses are just too great.
Also, the usual York automotive refrig. compressor converted to pump air will only produce about 10 SCFM @100 PSIG or equivelent to a 2.5HP air compressor. It will operate air tools for only a brief period of time, which for off road vehicles is sufficient. But for a shop it would be woefully inadequate.

I don't have any hard facts to back up these statements only 40 years of working with air compressors.

Have fun working with these ideas though.