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LPG
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Liquefied Petroleum Gas (LPG) is a mixture of hydrocarbons, mostly propane, and also propylene, butane, and butylene. In the United States, it is mainly propane, and hence the terms are used interchangeably in this context.

Propane is a by-product of natural gas processing or petroleum refining. It is a gas at room temperature, but turns to liquid when compressed. As a fuel propane is stored in its liquid state in special tanks that keep it under pressure (up to 20 bar), and is returned to its gaseous form before being burned in the engine (w1). A liter of liquefied propane has about 75% of the energy of a liter of gasoline The vapor released from any leakages is heavier than air (1) implying a higher risk for explosions for LPG than for CNG.

As a fuel for spark-ignition engines, it has similar advantages as natural gas (2). These include the near-absence of sulfur (3), and a higher proportion of hydrogen than gasoline or diesel, leading to about 10% lower CO2 emissions per energy unit. Its combustion leads to virtually no particulate emissions. In contrast to CNG, it has the additional advantage of being easier to carry aboard the vehicle (2), where storage tanks have a pressure of around 200 bar, LPG tanks with up to 20 bar are easier to manage.

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The use of propane requires that fueling, maintenance, and storage facilities be upgraded to appropriate standards or that a new facility be constructed. For example, propane storage and dispensing areas must be located certain minimum distances away from buildings, adjoining property, streets, alleys, and underground tanks. Building ventilation rates must be sufficient to remove propane from ground level. Maintenance facilities should be equipped with detectors for afamable gas. These devices can detect concentrations of propane before the vapors reach flammable levels ( 4).

Small propane refueling facilities for light-duty vehicles can be placed easily and safely aboveground (skid-mounted) and are very relatively inexpensive.

Unlike natural gas, which is lighter than air, propane is heavier than air and can collect in pits or under vehicles or cabinets. According to (4) however, safety does not appear to be a major concern, as many fleets regularly service propane vehicles indoors.

The fuelling time is comparable with that of gasoline or diesel fuel. Some fleets report 2 to 3 years longer service life and extended time intervals between required maintenance. However, manufacturers and converters recommend conventional maintenance intervals. Adequate training is required to operate and maintain vehicles (w2).

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LPG supply exceeds the demand in most petroleum-refining countries, so the price is low compared to other hydrocarbons. The OECD & UNEP ( 1) state that the price "is low compared to other hydrocarbons. Wholesale prices for consumer-grade propane in the U.S. have ranged between US$ 0.25 and US$ 0.30 per gallon for several years, or about 30% less than the wholesale cost of diesel on an energy basis. Depending on the locale, however, the additional costs of storing and transporting LPG may more than offset this advantage".

The Alternative Fuels Data Center (w2) agrees that propane costs in fleets typically range from 5% to 30% less than those of gasoline, and fueling station cost is similar to, or lower than, that for a comparably sized gasoline dispensing system.

The capital costs of facility modifications necessary for the distribution of LPG vary substantially, depending on the specific circumstances and equipment. A typical estimate for a 200-bus transit fleet is US$ 300,000 for modifications to one maintenance garage and US$ 700,000 for one propane fueling facility (4).

Modifying heavy duty diesel engines to LPG will reduce the efficiency significantly since the engines will become Otto engines.


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Propane gas is the most widely used alternative fuel, with about 5.7 million vehicles worldwide using it. It is widely used as a vehicle fuel in the U.S., Canada, the Netherlands, Japan and elsewhere. In Japan, 260,000 taxis, 94 percent of the total number of taxis, use LPG as their fuel. More than 350,000 vehicles run on propane in the U.S., according to the U.S. Department of Energy's Alternative Fuels Data Center ( w2).

4,175 public propane refueling stations have been documented in the United States, with industry estimates ranging up to 10,000 and more. There is also an established network of licensed propane conversion centers throughout the country (5). More than w10,000 bus, taxi and delivery services, and other fleets are fueled by propane (5).

According to (6), LPG vehicles comprise the largest portion of alternative fuel vehicles (AFVs), but their share has declined since 1992, when they made up 88 percent of all AFVs. As with natural gas, nearly all LPG vehicles presently in operation are retrofitted gasoline vehicles.

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The main obstacles to the widespread use of LPG buses in Latin American cities are likely to be the incomplete infrastructure (gas pipelines, refueling gas stations), the demand for additional training and knowledge about handling, inspection and maintenance, higher costs compared to diesel buses and lower driving ranges. Further challenges come from competition with natural gas, as well as the development of advanced diesel buses equipped with particle filters and catalytic converters using low sulfur diesel fuel, which compete with gas buses as they, too, become cleaner (4). According to (2), propane's major disadvantage is the limited supply, which would rule out any large-scale conversion to LPG fuel.

Propane is much better suited to use in light duty vehicles, including motorcycles, scooters, and three-wheelers, than in transit buses. Using propane in these vehicles, Latin American countries could improve air quality in their cities.

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Liquified Petroleum Gas (LPG)

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