freedomCAR & vehicle technologies program U.S. Department of Energy • Office of Energy Efficiency and Renewable Energy Just the Basics Liquefied Petroleum Gas

Although it is a fossil fuel, What Are the Emissions liquefied petroleum gas can help enhance the energy Benefits of LPG? security of the United States Propane vehicles emit about one-third and other significant emis- fewer reactive organic gases than sions benefits. Commonly gasoline-fueled vehicles. Nitrogen called propane, it is the most oxide and carbon monoxide emissions popular alternative fuel in are also 20% and 60% less, respec- the world. tively. Unlike gasoline-fueled vehicles, there are no evaporative emissions Less dependence on foreign What Is Liquefied while LPG vehicles are running or Petroleum Gas? parked, because LPG fuel systems oil, and eventual transition are tightly sealed. Small amounts of More than 350,000 light-and medium- LPG may escape into the atmosphere to an emissions-free, duty vehicles travel the nation’s high- during refueling, but these vapors are ways using liquefied petroleum gas 50% less reactive than gasoline vapors, petroleum-free vehicle (LPG or LP gas), while over 4 million so they have less of a tendency to vehicles use it worldwide. LPG is a generate smog-forming ozone. LPG’s mixture of several gases that is gener- extremely low sulfur content means ally called “propane,” in reference that the fuel does not contribute to the mixture’s chief ingredient. significantly to acid rain. LPG changes to the liquid state at the moderately high pressures found LPG Is a in an LPG vehicle’s fuel tank. Propane Vehicle Emissions Good Fuel Production LPG is formed naturally, interspersed for Fleet 100% with deposits of petroleum and natural Propane-fueled Vehicles gas. Natural gas contains LPG, water Service 80% Gasoline- fueled vapor, and other impurities that 20% Many propane 60% Vehicles must be removed before it can be Less NOx vehicles are transported in pipelines as a salable converted gaso- 40% product. About 55% of the LPG line vehicles. The 60% processed in the U.S. is from natural 55% from 45% from 20% Less CO relatively inex- gas purification. The other 45% comes Natural Gas Crude Oil pensive conver- Purification Refining 0% from crude oil refining. Since a sizable sion kits include amount of U.S. LPG is derived from a regulator/vapor- petroleum, LPG does less to relieve izer that changes liquid propane to a the country’s dependency on foreign gaseous form and an air/fuel mixer oil than some other alternative fuels. that meters and mixes the fuel with However, because over 90% of the filtered intake air before the mixture is LPG used here is produced here, LPG drawn into the engine’s combustion does help address the national security chambers. Also included in conversion component of the nation’s overall kits is closed-loop feedback circuitry petroleum dependency problem. that continually monitors the oxygen

Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable Just the Basics: Liquefied Petroleum Gas

content of the exhaust and adjusts the Fleet owners find that propane costs air/fuel ratio as necessary. This device are typically 5% to 30% less than communicates with the vehicle’s those of gasoline. The cost of onboard computer to keep the engine constructing an LPG fueling station running at optimum efficiency. LPG is also similar to that of a comparably vehicles additionally require a special sized gasoline dispensing system. fuel tank that is strong enough to Fleet owners not wishing to establish withstand the LPG storage pressure of fueling stations of their own may avail about 130 pounds per square inch. themselves of over 3,000 publicly The gaseous nature of the fuel/air accessible fueling stations nationwide. mixture in an LPG vehicle’s combus- tion chambers eliminates the cold-start How Safe Is LPG? problems associated with liquid fuels. In contrast to gasoline engines, which Propane is an odorless, nonpoisonous produce high emission levels while gas that has the lowest flammability running cold, LPG engine emissions range of all alternative fuels. High remain similar whether the engine concentrations of propane can is cold or hot. Also, because LPG enters displace oxygen in the air, though, A Strong Energy Portfolio an engine’s combustion chambers as causing the potential for asphyxiation. a vapor, it does not strip oil from This problem is mitigated by the for a Strong America cylinder walls or dilute the oil when presence of ethyl mercaptan, which the engine is cold. This helps LPG- is an odorant that is added to warn Energy efficiency and clean, of the presence of gas. While LPG itself powered engines to have a longer renewable energy will mean service life and reduced maintenance does not irritate the skin, the liquefied costs. Also helping in this regard is gas becomes very cold upon escaping a stronger economy, a cleaner the fuel’s high hydrogen-to-carbon from a high-pressure tank, and may ratio (C3H8), which enables propane- therefore cause frostbite, should it environment, and greater energy powered vehicles to have less carbon contact unprotected skin. build-up than gasoline- and diesel- independence for America. Working As with gasoline, LPG can form powered vehicles. explosive mixtures with air. Since with a wide array of state, community, LPG delivers roughly the same power, the gas is slightly heavier than air, acceleration, and cruising speed char- it may form a continuous stream that industry, and university partners, stretches a considerable distance from acteristics as gasoline. It does yield the U.S. Department of Energy's a somewhat reduced driving range, a leak or open container, which may however, because it contains only lead to a flashback explosion upon Office of Energy Efficiency and about 70-75% of the energy content contacting a source of ignition. of gasoline. Its high octane rating Renewable Energy invests in a diverse (around 105) means, though, that an LPG engine’s power output portfolio of energy technologies. and fuel efficiency can be increased beyond what would be possible with a gasoline engine without causing destructive “knocking.” Such fine-tuning can help compensate for the fuel’s lower energy density.

August 2003

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For more information, visit www.eere.energy.gov/vehiclesandfuels or call 1-800-DOE-3732