Re: [MV] Compressed natural gas

James Shanks (n1vbn@bit-net.com)
Tue, 17 Aug 1999 21:56:53 -0400

-----Original Message-----
From: jonathon <jemery@execpc.com>
To: mil-veh@skylee.com <mil-veh@skylee.com>
Date: Monday, August 16, 1999 11:13 PM
Subject: Re: [MV] Compressed natural gas

>
>>By compressed natural gas I think you mean propane and under several
>hundreds of
>>psi this actually liquefies at ambient temperature.
>
>I think he means compressed natural gas (methane). Liquid methane is
>alittle out of the realm of practicality. You cannot get liquid methane
>unless the temp is under -116 degF and then it's like 620 psi (strange but
>true: if you continue to compress methane and keep it above -116degF it
will
>never liquify, yet it's density will be higher than that of the liquid). I
>think the pressures for commercial CNG systems are running around 2500psi.
>This is becoming more common now a days. The big advantage for the home
>handyman convertion is that if you tap into your house gas system,
>(requiring a suitable compressor) you can fill up road tax free, that is
>until enough people do it then the gov will figure a way to take care of
the
>new menace.
>
>LP at 70 deg F is around 110 psi, or like 170 psi at 100 deg F.
>
>
>> Propane is normally used
>>since other acceptable gasses, butane for instance, will self freeze when
>>required to evaporate at an engine demand rate.
>
>This is only true if your drawing vapor off of the tank. The bigger
problem
>is that if your operating in cold climate the vapor pressure of n-Butane
>or iso-Butane could go to zero (gage) and you'd never get anything out of
>the tank. Butane boils at around +30 deg F. This would necessitate a tank
>heater or a pump to get it out of the tank if below +30 F. LP's boiling
>temp is like -44 deg F.
>
>
>>The systems usually require a special cylinder or vehicle tank with a dip
tube
>>into the liquefied gas and have a preheating device to ensure the engine
>>breathes no liquid.
>
>True, but the vaportizer/regulator job is to proved a very small negative
>pressure of LP vapor to the carb. It isn't so much a preheat as it is
>simply to keep the vaporizer from freezing up. Two types, either run
engine
>coolant thru it or the other type has a large set of fins and you place it
>in the cooling air outlet, if an air cooled engine. I believe that on a
CNG
>system the regulator unit must provide a very small posative pressure to
the
>carb. For safety reasons, this necessitates a more complex system.
>
>
>
>>They are far less polluting and wearing on the engine but can tolerate
>>compression ratios well above that even obtainable on aviation gasoline,
the
>>fork lift trucks invariably use propane because they run in enclosed
buildings.
>
>True, not to mention that you can change the oil on an LP engine and it
>looks new. I reuse it in one of my old beater trucks.
>
>
>>Power is slightly down on gasoline but its well under 10%.
>
>Fuel consumption/cost, in $'s per mile, is a little higher than with
>gasoline. ( or whatever your local currency & distance units are!)
>
>Try it, you'll like it!

Just for general knowledge Propane is rated at octane rating of 115 which
puts the ole gas engine in a new category if you want improved performance.
I use to haul it (propane) in an 18 wheel tanker delivering here there and
wherever.

James Shanks
The Line Below is my Ham Radio Callsign
n1vbn@bit-net.com
The line below is my Ham Radio Packet Address
n1vbn@N1VBN @ WB1DSW.NH.USA.NOAM

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