Sunday, January 31, 2010

The effect of temperature on natural gas

Some folks have asked about the effect of ambient temperature on CNG.

As the natural gas is stored in a fixed volume tank, the tank's pressure will vary in direct proportion to the temperature of the gas in the tank.  See the chart below - and here's how the Institute of Gas Technology (IGT) explains it in their 1993 document:

Natural gas (or any gas) when  confined in a fixed space will increase in pressure as the ambient temperature rises or decrease in pressure as the temperature falls.  This is true for natural gas in a vehicle's storage tank as well as the air in the vehicle's tires.  The magnitude of the change in pressure is a function of the size of temperature change, starting pressure, and the gas composition.  Since the term "natural gas" represents a broad range of gas compositions as distributed in the US, IGT used a mean natural gas composition.
The temperature-pressure relationship figure presented (below) can be used to determine the change in pressure corresponding to a change in temperature for natural gas.  Six reference lines have been plotted corresponding to six different starting gas pressures at 70 deg F.  As an example, point A represents natural gas in a storage container at 3,000 psig and 70 deg F.  Should the gas temperature drop to 40 deg F, one can expect the gas pressure in the tank to drop to 2,596 psig (point B)... It is important to note that the change in pressure does not represent a change in the amount of gas (energy) within the tank.  The gas simply contracted or expanded as a result of the change in temperature.

This source document and others like it can be viewed in The File Library of

Note that you can comment on this blog entry and all other entries posted here.  Please feel free to comment or ask questions. - Craig

Sunday, January 24, 2010

I don't have the heart to tell them that they got ripped off...

Unfortunately my fellow Oklahoman paid thousands more for the hybrid Civic and still pays more for fuel....- Craig

Saturday, January 23, 2010

Sunday, January 17, 2010

Update on my Honda Civic GX CNG experience

The car is working great - it was over 2,600 miles on it now.  As you can see on my mileage tracker, the longest range so far is 200 miles and the most natural gas I've refueled it with 6.1 gge.  The refueling ease has been a welcome surprise; there are less fueling locations, but the process is just as quick as fueling with gasoline.   The oil life indicator shows 70% oil life remaining so the oil change frequency is much less than a gasoline vehicle. 

This Google Map shows all the fuel stations I've used so far, and the furtherest destinations in the Honda Civic GX.  The Stroud fuel dispenser is located at the turnpike McDonald's/gas station - it's very convenient. 

It's very satisfying to be driving this car that is so cheap to operate and so environmentally friendly; while others around the US are having to wait and wait for the promises of plug-in hybrids.  We are so blessed to have the CNG infrastructure in Oklahoma!

View Craig's CNG Honda in a larger map

Here's the latest new station in Oklahoma City - just south of I-44 on Western Ave.

Right off I-44 on Western.

Saturday, January 2, 2010

Filling up in the snow at ONG's Okmulgee site

Filling up at ONG's Okmulgee site - very convenient as it is right next to Hwy 75 on the south side of town.  That's Hwy 75 on the left side of the picture - looking south.  Got almost 3,600 psig in the Civic CNG tank - this is the last Oklahoma CNG station when traveling south to Dallas on Hwy 75/69.  I'm going to see how many miles I can get on this tank to see if I can make the drive to Dallas on this route - it's 211 miles from this Okmulgee station to Clean Energy's Garland station.

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