88%__vs__90% methane

[peni007]

Is it me or does anyone notice a decrease in gas mileage when filling up at a station with a sign that states minimum 88% methane?

I have regularly used the Placentia station where the minimum methane is 90% and consistently getting 40MPG in my commute.

In my "test" to see if there is a difference, I have been filling up at the Trillium station for the last five tanks and mileage has decrease to 38MPG with all other factors being relatively the same.

Would anyone care to comment.

BTW I get great fills at Trillium with 4200 PSI.

[Jennifer]

Re: 88%__vs__90%

As a general rule, stations don't have any control over the methane content that is contained in the gas that goes through their station. (The exception would be LCNG stations, for example.)

Someone from SoCal Gas could answer this question better, but if our station and the Placentia station are fed from the same line, the methane content will be very similar. If the stations are not on the same main line, there could be some differences. Methane content in the gas will definitely change with the seasons and the sources that SoCal uses.

[Adrian]

Re: 88%__vs__90%

That's interesting, better fuel mileage on higher purity natural gas (90% CH4). I always thought the other 10-12% were ethane, propane and trace amounts of longer chain hydrocarbons which should have a higher Btu content and hence give you better fuel mileage for the same dispensed weight (5.66 lbs). Anyone else have any thought on this?

[jetboatjohnny]

Re: 88%__vs__90%

I dont really think it makes a significant difference. Maybe if we get some of that "HOT GAS" then maybe. Curtis, you have that map that Steve (So Cal Gas guy) drew up, are there any stations in that area? Santa Clarita maybe?
BTW..Hemet (RTA) station says 90% and is still 2.19! Gotta love CNG

[Idarusskie]

Re: 88%__vs__90%

who is to say that the other 10% or 12% is not co2.
or water vapor.

[Curtis]

Re: 88%__vs__90%

I dont really think it makes a significant difference. Maybe if we get some of that "HOT GAS" then maybe. Curtis, you have that map that Steve (So Cal Gas guy) drew up, are there any stations in that area? Santa Clarita maybe?
BTW..Hemet (RTA) station says 90% and is still 2.19! Gotta love CNG

I believe Santa Clarita is one of the stations pumping well gas. I'd have to dig up the map, or ask Steve at the Expo this weekend. Probably the Oxnard station too.

And Idarusky... with the Co2 and water vapor again???

[cngmike]

Re: 88%__vs__90%

If you want the highest grade of CNG go to barstow. LCNG.

[chromevader]

Re: 88%__vs__90%

I noticed that pumping at LB the other day, one pump said 88% while the other stated 90%.

Have we come to a conclusion on this? Is 90% better?

[Ben Cubbedge]

Re: 88%__vs__90% methane

88% Methane likely implies that the rest is atmospheric gas. I've been told that some stations, and even utilities, dilute the gas, and thus the BTU's so that they could sell more gas.

So, if you're experiencing poorer mileage, you'll also experience poorer performance, because the gas has fewer BTU's, and is less potent. However, if the remaining portion of the gas is Ethane and Propane, that would mean that the gas is far more potent then 100% Methane. It would be somewhere in the neighborhood of 1110 BTU's/SCF. Or, approximately 10% "hotter" then 100% Methane, which weighs in at 1010 BTUs/SCF. Basically, selling it by the "%" content Methane is a way to rip people off. It should be sold by the BTU, as is all gas on the wholesale market.

Gas from the wellhead has to be of "pipeline" quality, before we can transport it on Chesapeake's or Dominion's gathering system. Pipeline quality is around 1250 BTU's. Before it gets to the utility, the people from whom you buy your gas, its "stripped", a process wherein all the other gasses are removed, leaving 99.9% methane. This methane is shipped through the pipeline to whomever retails it, which is likely your utility company. So, when they get it, its 100% methane. When you get it, who the hell knows what's in it. However, it would stand to reason that, if your state standard is only 85% methane, then they'll introduce 15% Nitrogen, CO2, water vapor, or some combination thereof, thus increasing the profits.

So, they should sell it by the BTU, because that's how they buy it.