by Jennifer Olvera
07/03/2008
What LPG Really Is
Liquid Petroleum Gas - also called LPG, autogas, or LP Gas - is more commonly known in the U.S. as propane. In reality, however, LPG is a blend of propane and other hydrocarbon gases, such as butane. LPG is a byproduct that occurs during crude oil extraction and refining or from gas streams. It has a very high octane rating and becomes liquid when compressed, but reverts to a gas at normal temperatures and atmospheric pressure. Transporting LPG in its liquid state is ideal since it's extremely dense.
Benefits and Drawbacks of LPG
When used to power internal combustion engines, LPG is non-toxic, non-corrosive, additive-free, and doesn't contain tetra-ethyl lead. It also burns cleaner than traditional liquid motor fuels, such as gasoline and diesel. However, its energy density is lower than these fuels, resulting in fewer miles per gallon. Because certain types of internal combustion engines need lubrication from diesel and gasoline, it's possible that the use of LPG, which is non-lubricating, can damage valves and reduce the life of engines.
There are Different Kinds of LPG
It's important to use the right grade of LPG in order to prevent engine damage. Of the three kinds that are commercially available - propane, engine fuel-grade propane (or HD5), and commercial-grade butane - HD5 is the only engine fuel-grade propane. Standard HD5 requires a minimum propane content of 90 percent and propylene content that's lower than 5 percent. However, it's important to note that despite attempts to provide a standard in the U.S., the standards for HD5 are not universal since the concentration of propane itself can range between 50 percent and 100 percent. Its composition therefore ranges from country to country and location to location.
LPG Results in Power Loss
The use of HD5 results in a power loss of about 4 percent and up to an additional 20 percent among engines that have been converted to burn LPG. One of the ways this can be overcome is by using a supercharger or turbocharger to increase the volume of air that's burned with fuel in the engine's combustion chambers. Ways to enrich the oxygen content of the intake air are being investigated, but the findings aren't currently being applied to commercially available vehicles.
LPG Can Reduce Maintenance
It is believed that using LPG reduces the wear and tear on spark-ignited engines. Oil does not need to be changed as frequently, plus spark plugs and engines have been found to last longer than cars powered by gasoline. Typically, LPG-fueled cars start easier in cold temperatures, too, but the opposite can be true when it's hot. Propane's properties are highly affected by the temperature at which it's stored. When it gets warm, propane's volume increases; a safety fill-stop device ensures room remains in the tank so it cannot be filled to capacity. Because propane is stored under pressure and has a low viscosity, it's more common for it to leak through cracks, gaskets, seals, and pumps.
Jennifer Olvera, a graduate of DePaul University in Chicago, has been writing professionally for over a decade. In addition to covering the "green scene" for publications such as Where Magazine and Crain's, she has become one of the preeminent dining, food, and entertainment writers in Chicago. She has regularly been published in Chicago Magazine, Chicago Sun-Times, Chicago Tribune, Zagat, Citysearch.com, and Gayot.com.
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