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davisonh
#1 Posted : Thursday, June 11, 2009 2:05:32 AM
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You're about right street,but I think a gasoline engine's about 150-200 psi but a diesels' much higher,around 400-1200 psi or so.Has to be to ignite the vapor using extreme compression only as you know.You know,here's a thought.How about using a semi hermetic refrigerant motor compressor.An old one.You can find loads of old rooftop ones in the 3-25 hp range.The condensers usually go bad or someone forgets to keep up the refrigerant.No problem with explosion,they are semi  hermetically sealed.Problem with an engine  as a compressor is you don't want to add any air to your natural gas so your intake manifold'll have to be sealed up from any air getting in.That can be extremely explosive!Then you gotta cool it because pressurizing any gas creates heat.Heavier the gas the more heat generated.Natural gas is pretty heavy,it tends to sink,not as much as propane does but it still will create heat.Oh,as far as hp's concerned,I'd guess since you're not compressing massive volumes of gas I would start off with a one horse and see where that gets you.Thats the good news.If it works well street(here comes the electrician in me)ya have to wire the equipment for a Class 1 Division 1 location or terrible things may happen,lol.sorrie,dont want to scare you!Flashback arrestors @1000-1500 psi are common for oxy-acetylene torches,try that route.Go to any welding supply or gas supply house and I think they'll be able to greatly help.As far as pipe size,since high pressure low volume,max size I'd use is 1/4 inch stuff,preferably stainless because NG straight from the ground tends to be very strong acid-wise.Do you have a lot of hydrogen sulfide in it?

Pat Miketinac
#2 Posted : Saturday, June 13, 2009 3:35:12 AM
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Wow. If you had a 3" piston, I think the piston load would be over 20,000 pounds with the surface area over 6 square inches. Hard to turn.

You may be interested in a device I used to pump up air/oil struts on aircraft. It multiplied the output of the shop compressor. It had two long cylinders of different diameters attached end to end. Air applied to the large piston provided much higher output from the small one. It cycled back and forth with valving. In your case, you would need a way to recover the gas exhausted by the valves. The neat thing is that it powered itself with compressor output.

Another thought would be to refrigerate your vehicle tank to allow more to flow in, then let it warm up as you drive. Good luck!

StreetLegal
#3 Posted : Saturday, June 13, 2009 6:44:47 PM
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Davisonh: I should've been more specific - I was wondering what the psi in an engine cylinder was when the fuel/air mixture ignited.  As for the refrigeration compressors, I've never seen any refrigeration equipment that dealt with more than 350 psi or so.  If I put 1,500 psi into such a compressor and expect it to put out 3,600, it seems to me something's likely going to come apart.

 

The flashback arresters I've used are downstream from the regulators, and so only are required to deal with psi in the hundreds (or less), but I'll do more research into them.

I've not smelled any H2S, but it may be present.  Come to think of it, years ago I had an H2S safety certification.  The gas field where this well is located is one of only a few in the US that contains arsenic - yum!   Stop by and I'll grill you a burger

And no, I ain't going down the explosion-proof wiring road - I don't care what you spark-tricians say 

Last week, I installed a valve and a quick-coupler on my (50 psi) gas line - I then connected all my air hoses to it and used a weed burner torch to singe all of the cochilla weed that had sprouted in my yard - cool!  It works as well as Gramoxone and is a lot healthier for the applicator.

I am still tweeking on my gas-absorption, gas-fired chiller, but last week, it was putting out 37 degree F water. 

I have some questions about water heater/boiler burner controls - I'll make another post for that.

--------

 

 

Pat:  You are correct, it will be hard to turn.  I suppose it's just a matter of doing the math to determine the horsepower/torque required.

I am familiar with the pressure amplifiers that you mentioned.  I have two issues with those, one being the waste gas and the other being the initial cost. 

The waste gas could be captured and routed to a low pressure storage tank that would feed my house - that's probably not a big deal.  If the storage tank were full, the gas would vent to atmosphere.  I could just dump the waste to atmosphere since I have no cost in it anyway, but it's just not in my nature to be wasteful like that.

I spoke to a guy at Haskell about such an amplifier.  As I recall, the cost was going to be $12,000 or so.

I've beat this thing around for months, and I still find myself going back to a simple, one-lung gas engine converted to a compressor - all I have to do is build the intake/exhaust manifolds, deal with possible flashback, and turn the *@#^ thing!

Thanks for the input, guys - I'll keep working on it.

 


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davisonh
#4 Posted : Sunday, June 14, 2009 2:04:57 AM
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Sorry street I thought you meant intake pressure.All I can say is try the one-lunger see if the 8:1 does what you want it to do.Really I doubt you'll have trouble with flashback so long as you keep the heat down and the air out of the fuel. I'd do it!

Pat Miketinac
#5 Posted : Monday, June 15, 2009 2:13:57 PM
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O.K., here's another weird idea. Add a spacer to the cylinder head to get a compression ratio a little better than 2:1. Then, pressurize the crankcase with 1500 psi cng. I think this would reduce the compression load on the piston by half. The crank would need pressure seals like a 2-stroke, and the vent would need to be plugged or used to supply the 1500 psi cng. This would also allow using unregulated cng to the intake. Add a scattershield, and see what happens! A 2-stroke engine might even work as a compressor if it had oil injection to the bearings like my '69 Suzuki bike. Maybe seal the cylinder exhaust port up to the piston and take the output from the sparkplug hole with a check valve. The compression ratio might not matter this way, it would be pushing directly against your fuel tank pressure. I think an oil separator would be needed too.Again, just ideas. I was an aircraft mech., not an engineer. I converted my truck to propane and loved it. The oil stayed clean, no carbon buildup, ran great, equivalent to 100 octane. I sold it when they changed the law here forcing a high flat annual road tax on propane to be paid a year in advance! Sad, no? @%">*@%^ government.
StreetLegal
#6 Posted : Monday, June 15, 2009 6:12:49 PM
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hmmmm...hadn't thought of crankcase pressure.  I doubt the flat walls and square corners of a typical crankcase would stand 1500 psi. If I vent the crankcase, and with 3600 psi trying to push the oil out of the rings, I wonder how long my rings would last.  And I like the idea of scatter-shields.

A 2-stroke engine would be twice as efficient as a 4-stoke, but 2-strokes are harder to find and seldom have a "workable" output shaft.  A 4-stroke with off-the-shelf compressor valves would be best.  That way I could make pressure on each stroke.  But then I'd have to build (read: $$$machine shop$$$) a special head to hold the valves and manifolds, and I'd still have the issue of block pressure.

I have an old graco airless that has a reciprocating hydraulic cylinder that drives the paint fluid pump, and it develps pressure on both the up-stroke and down-stroke.  If I took the fluid (paint) pump off and installed a small, double-acting pneumatic cylinder with input and output check valves, it might work purty good.  I suuspect it would be mighty slow, but then I could let it work all night if necessary.  Drawing 10 amps, if it ran for 8 hours, the electricity would cost me aprx $1.73.

Maybe for now I just need to install more and/or larger tanks and only fill the tank(s) half full - and let you guys stew on it for a while

 

Thanks again for the input

 


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LaserBillA
#7 Posted : Tuesday, June 16, 2009 3:29:13 AM
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I just don't see any way of modifying a engine to handle those pressures.

I had a DOT approved NG cylinder, however it was destroyed in the fire. Now I have to try and figure out the replacement cost for the Insurance company.

My plan was to use a pressure washer or a hydrolic pump. It's not that hard to set up a pump with a cycling oiler that feeds in 10% oil and then recovers the pump oil on the other side.

tavey
#8 Posted : Tuesday, July 28, 2009 1:38:41 AM
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Hey Street,

I have seen a reciprocating compressor do some pressures close to what you want to acheive at the paintball range. The kids won, dammit. They were pumping around 3,200 psi with a 7.5 HP electric motor belt driving a smallish but heavy built 2 cylinder 2 stage pump. It had a label on that the word "Diver" in it. I'm not a scuba diver but I'm betting that's what the unit was built for. Just a thought! Next, I work around aircraft which use high pressure oxygen and nitrogen, both of which are used in the 2,500 to 3,400 psi range. Both are boosted to the needed pressure using an intensifier so that the O2 and nitrogen can be completly used up out of their cylinders. Haskell makes all the units I've seen. They use either shop air (cheap) or nitrogen (out on the flight line) to drive a large cylinder which move a small cylinder (ratio) to get the pressure up. Google intensifiers, they come in many ratios, volumes and pressure ratings to the many many thousands of pounds (and dollars). You could use an NG fed 4 stroke motor to run a home made compressor to run an intensifier to pack the fuel into the cylinder on your truck to screw Obama and Richardson out of the road tax and make us all proud. By the way, I have a brand new surplus, never used 1999 model O2 intensifier in the garage if your interested. no kiddin'.

T

StreetLegal
#9 Posted : Saturday, August 01, 2009 3:50:26 PM
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tavey, thanks for the suggestions.  I'm familiar with Haskel, and am interested in the intensifier you have.  Do you have a model # and/or the specs on it?


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StreetLegal
#10 Posted : Saturday, August 01, 2009 3:50:26 PM
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I want to turn a single cylinder gasoline engine into a compressor head.  I have in mind an 18HP or so, 4-stroke, horizontal shaft, lawn mower-type engine with about 8:1 compression ratio.  I will belt drive this compressor with an electric motor (or preferably with a natural gas-powered engine).

I will feed the suction (intake) side with up to 1,500 psi of raw natural gas.  I am looking for 3,600 psi on the pressure (exhaust) side.  This compressor will be used to refuel a cng vehicle, and a high volume out of the compressor is not necessary.  In theory, I will fill my cng fuel tanks half-full with the 1,500 psi of pressure that I already have, then pressure-up the top half with the compressor. 

Store-bought compressors for this purpose are $10 grand or so, and conventional air compressors will not handle the high pressure - so what's a redneck to do but build one? 

 

My questions:

How much psi does an internal combustion engine normally develop in the cylinder  -  do I need to worry about blowing the head off my compressor?

Any guess as to the horsepower I would need to turn such a compressor?  I know that depends on rpm, but what would you recommend and why.

If the compression ratio is 8:1, then I assume I would need an input pressure of 450 psi.  Do they make flashback arrestors with that high a pressure rating?

Any other warnings or words of wisdom?

Thanks

 

 


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