Propane convert to CNG to power a tractor?

I don't know if this is possible but in PA we have a booming natural
gas industry. They are opening CNG filling stations around us.
Could you, in theory, run a propane tractor on CNG(compressed
natural gas). Would it require a different regulator? Carburetor? I
know the furnace in my cousins house had a new burner nozzle
put in to convert from CNG to propane. Could it be done? This
doesn't include the thought of how to fill it remotely, with out
driving it to the station every time. I'm just curious.


If no one thought of this I call dibs on the patent.

I know they make generators to run on ether propane or natural gas. So I would think it is just a mater of adjusting the carb some how ie bigger/smaller jets.
Ypop

Sorry, but you're not the first to think of this (and neither am I ). You would need to have LIQUIFIED Natural Gas instead of just COMPRESSED Natural Gas in order to have any significant amount of gas to perform a significant amount of work. I would believe that the gas metering equipment would be the same and that the only thing that you would need to change would be the diameter of the metering orifice. Now whether the LNG would provide as much energy as the LPG - that I don't know; but in my humble opinion I would believe that it is possible. But would it be COST EFFECTIVE in the long run ? ? ?


:>)

Ok I was thinking the whole time it would have to be liquified NG. So I'm not to far off. Is that even sold in portable container? Like propane tanks? I am not going to do this nor do i ever have any plans but I am just a thinking outside the box.

Liquified natural gas has to be kept at -260° F to remain liquid. That could be a problem, out there in the hayfield. . .

These guys are right up the road from me. The technology has been out there for some time. Probably too expensive for the average Joe but very doable for someone running a fleet or something to save big bucks over time.
Alternative Fuels

Propane is stored in your tank at a little over 100 PSI. CNG needs a tank that has to be rated for a PSI rating way over 1000. Can you live with that?

Why would it have to be liquified for tractors? Apparently compressed is adequate for road vehicles.

(quoted from post at 00:42:29 11/05/14) I don't know if this is possible but in PA we have a booming natural
gas industry. They are opening CNG filling stations around us.
Could you, in theory, run a propane tractor on CNG(compressed
natural gas). Would it require a different regulator? Carburetor? I
know the furnace in my cousins house had a new burner nozzle
put in to convert from CNG to propane. Could it be done? This
doesn't include the thought of how to fill it remotely, with out
driving it to the station every time. I'm just curious.


If no one thought of this I call dibs on the patent.

Click to expand...

A Goggle search reveals that:

Substituting LPG for CNG

Because LPG produces more energy than CNG, it cannot simply be substituted for natural gas. Only gases that have the same Wobbe index are interchangeable. For LPG to have the same Wobbe index as CNG, it has to be mixed with air. A 60:40 ratio for LPG:air mixing is common but it depends upon the composition of LPG because LPG itself is a mixture of propane and butane. This mixture of LPG and air to substitute natural gas is called synthetic natural gas (SNG). Use of SNG is common before the CNG distribution network is fully operational.

Definitely doable but I don't think it would make economic sense unless you run your tractor from sun up to past sunset.
It would have to be compressed natural gas as storing liquefied natural gas requires a storage tank that will keep it really really cold.

LNG isn't practical due to storage as others have mentioned. CNG could be used, but you would need some pretty big high pressure saddle tanks. For high load use you would be better to run a diesel/CNG dual fuel system. Do some searching for Cat or Deere generator info. They have also used this setup on city busses.

The carburetor changes shouldn't be too big a problem, lots of engines running on CNG. the tanks might be a bit of a problem, expensive and very heavy. I don't know if it would be feasible to have a fueling station at home, but if you have one nearby.

One other thing to consider is the SIZE of the tank you would need. I have 2 LP tractors that I use regularly. One is about 60 hp and the other is about 75. The 75 hp one will hold 33 gallons of LP with 80% in the tank and I can run that tank dry in about 10 hours just running the square baler with it. That tractor on a full load will use about 6 gallons of LP an hour and will eat a tank of fuel about every 5 hours. Just how big of a tank would you have to find space for on a tractor to even run a half day of moderate work with it?

It would work just fine, the distance from the filling station, and cost of course, would be the biggest hassle. The fuel regulator will need some tweaking. I have changed 454 Chevies back and forth between CNG to LP, the only change is the diaphragm in the regulator side of the carb. As far as I know NG and LPG carbs are not like a clothes dryer, not simply an orifice that vapor squirts through, you need a little more sophisticated means of metering the fuel for varying loads. There are literally thousands of engines around me burning CNG and having no problem making significant hp.

LNG needs to be converted to CNG in order to run in an engine whether it's metered and spark ignited or fogged into intake of an electronically controlled diesel as substitution (the electronics will throttle back the diesel injection amount if intake is fogged with natural gas, you can substitute up to about 50% with CNG without making any software changes to the engine, to get higher substitution ratios you need to have some new software development. You can run CNG in a spark ignition engine if you have a way to accurately throttle gas delivery but it can be done. You're just limited to how much fuel you can carry.

LNG is held at cryogenic temperatures at relatively low pressures (<50 psig IIRC). It has to run through a heat exchanger to vaporize the liquid so it can be utilized. It's much more energy dense than CNG.

CNG:
1.1-1.6 lb/gal
23000-34000 BTU/gal
2500-3600 psig tank pressure
Ambient temperature in tank

LNG:
3.5 lb/gal
75000 BTU/gal
10-50 psig tank pressure
-259 deg F tank temperature


In an application where a fuel tank is completely used up in a shift and runs day in and day out year round like mining equipment, locomotives, and marine applications LNG is very attractive to use as a fuel. Farm equipment is not a very attractive application of LNG. You also need very expensive and complication filling tankers and a liquefaction plant to liquefy natural gas.

I know more but am not at liberty to say anything everything I recited here can be found online.

Get ready to purchase large heavy 4500psi tanks and pressure test them as per your state's regs.
Consider the price of a compressor and electricity.
Cryogenic storage is not even a consideration.

I think that storage of a compressed gas versus a liquified gas is the issue. It takes a LOT more storage for non liquids. Once it is a vapor, you are down to BTU differences in the two gasses.

Can you do it yes, will it be cheap, no. Buickanddeere hit the high points already regarding the pressure and tank inspections.

There are home fill stations available, but not exactly cheap either, assuming you have NG at your house.

If you have a stationary application like a generator set, then gaseous natural gas would work well and could be very economical. Mobile applications would require CGN. Other liquid fuels would be better suited for mobile equipment.

"Why would it have to be liquified for tractors?"

To provide enough capacity in a relatively smaller
tank so that when it is converted back into CNG
that you would have enough volume to do a days
work, without having to have a monster sized tank
to hold enough CNG to do the days work. But
because LNG is extremely COLD, it would need to be
in TRIPLE walled, high pressure "Dewar Flask"
tanks - (think of a large, steel, triple walled
"Thermos" bottle).


:>)

Our local natural gas company run all their trucks on it. They have a filling station at their business location that customers can use also. Whether anybody else uses it I don't know.

It might work, but I doubt that it would ever be practical. And it would be expensive.

Natural gas carries less energy per unit of volume than Propane, so you would need to use a bunch more to get the same level of power production. Another disadvantage of natural gas as compared to propane is that natural gas will not liquify at nearly normal temperatures and pressures like propane will, so the storage tank would need to be changed to something a LOT stronger to handle the extreme pressures needed to carry enough natural gas to get anything done.

Years ago the agency I worked for tried an experiment with compressed natural gas powering an early 80"s Chevy Caprice. The car also retained the normal gasoline tank and carb, but was supposed to be run on the CNG as much as possible. The 3 heavy tanks nearly filled the trunk of the Caprice sedan and were heavy enough that the car sat down a bit in the back. There was almost no room to store other things in the trunk.

The car ran OK, although it was much more powerful using the gasoline system. Maybe it could have been tuned, or the engine built to run better on the CNG, but the engine was a standard 350 only slightly modified to add the CNG system. The worst problem the guys who had to use the car found, was that even with the 3 CNG tanks that filled the entire trunk, it was not possible to go through an 8 hour shift using CNG without filling up. And the process of filling up took about a half hour, which was deemed a huge waste of time. And the tanks could only be filled at one place that was set up with the high pressure CNG system.

So although the CNG fuel cost was much less than the cost of gasoline to go a given distance, the experiment was considered to be a failure. Eventually the car was converted back to a gasoline only system. I wasn"t involved in getting the car set up for CNG, but I believe that the cost of the conversion had been paid for by the local natural gas company. I assume they got the components back when they were removed from the car. I never heard what the conversion would have cost otherwise, but my guess is that it would have been at least several thousand dollars. Those tanks were really hefty.

CNG is something to think about, but in my opinion, it would not be a bit practical to try to run an old tractor on CNG unless you want to do extensive and expensive modifications to the tractor. Could a person get an old propane tractor to run using natural gas and only a slightly modified system? Probably, but it would have no range at all with the existing tank at a safe pressure level. I would not waste my time on it.

Might there be tractors in the future that are set up to use CNG? I think it is very possible, as it appears that our country has a vast amount of natural gas that can be recovered. But I think such a tractor would need to have huge tanks to store enough CNG to get anything done. Good luck!