CNG-Compressed Natural Gas as a Fuel?

Paolo,


Propane is cheaper, safer and easier to use....
CNG = BOMB.

I am going to go with E85 in my Ferrari within 5 years..


See photo of a CNG Honda,,....!
Do you see any chance that the driver survived...?

Ciao,
Edwardo
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Not sure why propane bomb would be safer than CNG bomb? But the cool thing that could make your idea happen would be if there was an easy way to compress your home NG as it comes out of the wall to a CNG in a tank for your car. As far as running a car on it that would be an easy conversion IMO.

 

LPG = 150 psi
CNC = 3600 psi

 

You might be on to something.

Converting an older carburettor equipped engine to run on CNG would be an interesting R&D project and something I've been considering as a Winter project here when things slow down.

It appears that there isn't much in the way of ready-made systems that can be installed on older vehicles. This doesn't mean that it can't be done however.

The natural gas infrastructure for refueling isn't very extensive yet (none in Minnesota) and in the Midwest, the ethanol lobby has gobbled up all the public dollars available to fund their folly. I expect that before long E85 will be phased out as it's an inefficient fuel that without public subsidy would be more expensive than "foreign oil".

Home systems for refueling are available from FuelMaker Corporation. The system costs a few thousand$ and fills the tank overnite.

As to safety, it's true that the stored pressures for CNG are much higher (like a Scuba tank) but natural gas is lighter than air and doesn't tend to "pool" in low areas (like much heavier Propane) and seek out pilot lights. Natural gas is generally regarded as being safer.

 

Having some experience in this, I would say no. One company I used to work for was using propane to operate their bucket truck.
There were some advantages such as the following.

Cleaner burning
Cleaner OIL
Cheap to fill
Lower pollution.
Higher Octane.

Against:
Storage tank in the vehicle
How long does the tank last before replacement
How far do you want to drive to fill up
Less power, so advance the timing
Refit the carbs, you shouldn't use your existing carbs,
Higher maintenance on the control components
Valves and rubber components can leak and they do wear out.
It make great engines fires
It is harder to start the engine in colder climates.
Certification is required by qualified personel
You can smell it, but you can't see it, when it leaks

shall I go on?

 

CNG is Compressed Natural Gas

Propane is Liquified Petroleum Gas

They are quite different.

 

As others have said you want to use propane, not CNG. I had a truck that ran off propane. The prohibiting factor is the large cylindrical tank. No place to put it in a small car.

 

Perhaps you weren't paying attention.

CNG is Compressed Natural Gas = American source, lighter than air

Propane is Liquified Petroleum Gas = Foreign Oil source, heavier than air

They are quite different.

 

The immediate problem I see is the huge pressures the methane must be at in order to have enough fuel to go a reasonable distance. Here are the heats of combustion for the fuels:

n-ocatane 1303 Kcal/mole C8H18 - 114 grams
propane 526 C3H8 - 44 grams
methane 211 CH4 - 16 grams

Roughly, as far as heat of combustion is concerned, they are in the same ballpark on a per gram basis. Methane has the highest value.

Given that, one has to compress methane to very high pressures to get it anywhere near what n-octane or propane possess on an energy per volume content. The density of liquid propane is about 31 lbs/ft**3. At 5000 psi, the density of methane is about 14 lbs/ft**3.

I don't see how to contain it given how frequently cars are smashed.

 

A properly engineered pressure vessel (or several smaller ones), thoughtfully located in the vehicle shouldn't be any less safe than the 20+ gallons of gasoline that cars currently carry in thinwall metal or plastic tanks.

The point of the "Picken's Plan" isn't that CNG is the ultimate fuel, only a less expensive "bridge" to whatever is. It's available here, now and conversion of a vehicle is a feasible proposition.

Other fuels like hydrogen and coal (no idea what you would do with that) are possible but have their own engineering obstacles that prevent any short-term use.

Just to restate it, Propane (LPG) is just another distillate from crude oil like gasoline. We are buying it from countries that are screwing us on the price and we need to stop.

 

True, and this raises another advantage of CNG over Propane... CNG is lighter than air, and so dissipates readily if there's a leak. Propane is heavier than air, and so can pool in the bottom of a trunk (for instance), rather than dissipating. Our utility used many propane forklifts with the tank on top of the vehicle, so that wasn't a concern. We also tested some CNG Cavaliers, borrowed from the local nat. gas utility. I've seen film of tests of CNG tanks, and IIRC, they have even been tested to withstand pistol cartridges. At the very least, they are tested to withstand almost any conceivable car accident scenario. Leaks are another issue, though, and I'm not sure of any record of CNG tanks actually failing, if they've been properly maintained and inspected during their service life.

 

Running upwards of 3000 psi, I wonder if the tanks need to be removed and be Hydro-tested every 5 or so years like the scuba tanks? I suspect they would require that running these pressures.

Pistol round safe or not, I sure would want a stout roll tube structure around one of those tanks with the valve facing sideways. Those TV ads have me thinking about an experiment in the future as well.

Dave

 

The tanks would require periodic re-certification just like other pressure vessels. In addition, the fueling equipment from FuelMaker is expected to be remanufactured after 5 years (can be done twice). This isn't cheap, this is really just a stop-gap system until someone develops a better one.

 

Then why did the NHRA outlaw on-board compressed air tanks decades ago? (guys got the idea to inject air from scuba tanks into the carburetor for a "turboless" turbocharger effect) NHRA outlawed it because of fear that the tanks would explode during a crash.

I wouldn't want to be anywhere near some ratty car powered by a 3000PSI CNG tank.

 

NHRA rules are written by lawyers.

No "real world" knowledge required.

 

I recall a guy that ran NHRA a few years ago on natural gas..the car was called "Natural Gasser". I don't recall his name, (Jose Melendez or something like that?) but ran the car successfully for years. Not sure if he's still running it or not. NHRA didn't outlaw compressed air tanks decades ago,(maybe outlawed them injecting it into the engine) there's still cars that use air shifters, we used them on Pro Stock cars up until the mid-nineties, when they said "shifting had to be a direct mechanical function of the driver".
But I'm fairly sure air shifters are still allowed in the sportsman classes.

 

I don't have access to my old Hot Rod magazines, but somebody wrote a letter asking about the feasibility of directing compressed air into the carburetors as an alternative to supercharging. They replied that it had already been done and showed a picture of a rail dragster with compressed air tanks mounted between the front frame rails. Then they indicated that it was later outlawed for fear of crash explosions. That's just what I read in the magazine.

 

Can't answer for NHRA, and not trying to be a Gas Industry proponent. But I'm sure CNG tanks are over-designed, to hold pressure required and also withstand impacts from crashes. But I agree that I'd also want extra structure to help protect the tank.

 

Here's a Powerpoint presentation that presents design and testing of CNG tanks. Also shows a gunfire test starting at slide 29. I can't tell from this if the gunfire test is required by codes, though, as part of the test standard.

http://www.cleanvehicle.org/technology/CNGCylinderDesignandSafety.pdf

 

They're going to have to rewrite a lot of laws if anybody goes the CNG route. Propane tanks going through tunnels are regulated. http://www.travelriver.com/forum/viewtopic.php?t=1076 and other links. Imagine a propane or CNG tank exploding in a tunnel. A perfect oven.

 

Kind of like a gasoline tank truck?

 

gas and propane tankers are in fact forbidden from some routes.

 

huh? there are already many CNG vehicles.