Posted by Joe Leydon [108.162.237.151] on Friday, February 17, 2017 at 10:03:06 :
In Reply to: what is CNG ??? posted by The Dodge Boys [172.68.65.183] on Friday, February 17, 2017 at 06:55:58 :
I read the posts concerning CNG and LPG and decided to pull some background info and post it for those who want a little more information (I can't offer a lot on how to fix or restore PW's but chemical engineering is in my toolbox :-))
LPG
LPG (liquefied petroleum gas)—a really convenient, super-pressurized gas stored in liquid form in a tank, canister, or bottle.
What is LPG
The basic idea of LPG is simple. If you're far from a gas main (the ordinary system of natural gas supplied to buildings through a network of pipes), simply get your gas from a large fixed tank or a portable canister or bottle. As its name suggests, LPG is a fossil fuel closely linked to oil. About two thirds of the LPG people use is extracted directly from the Earth in the same way as ordinary natural gas. The rest is manufactured indirectly from petroleum (crude oil) drilled from the Earth in wells in the usual way.
Propane and butane
Chemically, LPG is a mixture of two flammable but nontoxic gases called propane and butane. Both of these are hydrocarbons (their molecules are made from different combinations of hydrogen and carbon atoms): propane molecules (C3H8) have eight hydrogen atoms attached to three carbon atoms, while butane molecules (C4H10) have ten hydrogen atoms bonded to four carbon atoms. LPG sometimes contains a variation of butane called isobutane, which has the same component atoms (four carbons and ten hydrogens) connected together in a slightly different way.
Exactly which of the gases is present in LPG depends on where it comes from, how it is supplied, and what it is being used for. LPG typically contains a mixture of butane and propane gases, and tiny quantities of other gases are also naturally present. Since LPG is normally odorless, small amounts of a pungent gas such as ethanethiol (also known as ethyl mercaptan) are added to help people smell potentially dangerous gas leaks, which might otherwise go undetected. Pure butane tends to be used more for small, portable LPG supplies in such things as boats and gas-powered barbecue stoves. Since butane doesn't burn well at low temperatures, portable canisters often contain a blend of 20 percent propane and 80 percent butane; propane has a much lower boiling point so it's less affected by freezing temperatures and generally better for year-round outdoor use in cold climates. Larger household tanks are more likely to contain a majority of propane (typically 90 percent propane in North America).
As far as propane burning hotter it is really negligible:
Heat of combustion propane - 21,600 BTU/lb
Heat of combustion butane - 21,400 BTU/lb
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