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Tennessee County Municipal Advisory Service

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Propane for Tennessee Fleets

Reference Number: MTAS-1320
Tennessee Code Annotated
Reviewed Date: September 07, 2016

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Propane, also known as liquefied petroleum gas (LPG), is an odorless, non-toxic hydrocarbon gas at normal pressures and temperatures. When pressurized, it is a liquid with an energy density 270 times greater than its gaseous form. Aside from scientific terms, propane is used to power roughly 190,000 vehicles in the United States and more than 14 million vehicles worldwide. It is a smart choice for many fleet applications including school buses, shuttle buses, taxis, and light-duty trucks. Many people may ask what the differences are between propane and compressed natural gas (CNG). While natural gas occurs in nature as a mixture of methane and other gases, propane is actually a byproduct of both petroleum refining and natural gas processing. Natural gas must be cleaned before being used, and byproducts of this process include hydrocarbons such as propane in addition to butane, ethane, and pentane. The difference between propane and natural gas in domestic use comes down to their energy efficiency, cost, compression, storage, and risk factors.

Propane provides more energy per unit of volume than compressed natural gas. While propane is usually measured in gallons (or liters), natural gas is found in cubic feet (or cubic meters). Natural gas provides more than 1,000 BTUs per cubic foot (0.0283 cubic meters); the same volume of propane in gaseous form provides about 2,500 BTUs. This means that propane contains about two and a half times more usable energy content. So, less propane is needed to produce the same amount of energy as compressed natural gas. Both propane and compressed natural gas also can be used to power alternative fuel vehicles. Vehicles that run on either type require special tanks to hold the fuel; many cars are actually bi-fuel, which means they have additional tanks to hold gasoline. CNG must be kept at much higher pressure than propane, so the tanks are often larger and heavier, which can lower the vehicle’s mileage. Vehicles that run on CNG tend to be more expensive than those that use LPG. Also, propane has a narrow flammability range, and its tanks are 20 times more puncture-resistant than gasoline tanks.

Questions being asked are how a propane vehicle works and can they perform comparable to other types of vehicles? Propane vehicles operate much like gasoline vehicles with spark-ignited engines. They also are similar to their gasoline counterparts with regard to power, acceleration, and cruising speed. Two types of fuel-injection systems are available — vapor and liquid injections. In both types, the propane is stored as a liquid in a low-pressure tank. In a vapor-injected system, liquid propane is controlled by a regulator or vaporizer, which converts the liquid to a vapor. In a liquid-injected system, fuel is delivered to the combustion chamber, or intake port, in a liquid form. This publication guides you through the costs, the benefits, several examples and more to ensure a higher level of knowledge for this efficient type of energy.

Cost (Vehicles and Propane)
As far as the price for a propane vehicle, original equipment manufactured (OEM) light-duty propane vehicles can cost several thousand dollars more than comparable gasoline vehicles. However, due to federal tax credits, it may offset the increased vehicle cost. Many states have additional incentives that further support the purchase of a propane vehicle. Vehicle conversions may qualify as well for tax credits and other incentives. One of the driving forces for the popularity of this type of energy are lower maintenance costs. Propane’s high octane rating and low-carbon and oil-contamination characteristics have resulted in documented engine life of up to two times that of gasoline engines. The price of propane typically is based on the volume of fuel used. For the best success, fleet operators should develop relationships with their local propane marketers and station operators, who can provide them with the fair pricing and help them establish on site infrastructure at  little or no cost if a fuel contract is executed. If no relationship is formed, the fuel price may be equal to or higher than gasoline. Local propane marketers are present in almost every community across the United States and can provide expertise and assistance.