Green Ways 2Go from time to time publishes articles of common interest to its Customers, wanting to investigate Alternative Fuel solutions. This article serves to provide the basic information when investigating Propane Autogas for transportation potential use. Call Green Ways 2Go for more details on fuel storage, dispensers and conversion solutions for your fleet. We deliver solutions!
When propane based fuels are used as alternative transportation fuel in the US, the fuel is commercially available as a specified quality, and the term “Propane Autogas” or simply “Autogas” is used to define this quality. Autogas is a mixture of propane with smaller amounts of other gases. According to the Gas Processors Association’s HD-5 specification for propane, and per the US Department of Energy’s Alternative Fuel Data Center, this grade of fuel used must consist of at least 90% propane, no more than 5% propylene, and 5% other gases, primarily butane and butylene. Much of the available autogas is at least 95% propane.
Propane Autogas is in the family of Liquefied Petroleum Gases (LPG), also called Liquid Propane Gases or LP Gases. In the US, propane autogas is produced from processing of natural gas and in the refining of petroleum, in approximately equal portions. The composition of propane autogas varies, primarily based on a range of proportions of propane and butane, depending on the source. The term “liquefied” comes from the fact that the gases are in liquid form before extraction (i.e. underground and under pressure in the well) and turn to gas, or partly gas, under lower pressure surface conditions. For simplicity, technical comparisons for autogas are often based on propane. Outside of the US varying compositions of LPG may be used to fuel transportation.
Like gasoline or diesel, propane storage tanks require regular filling. There are many available regionally propane autogas companies that arrange scheduled filling of stationary storage for fleets and retail fuelers. Centralized propane storage facilities are used to fill up the refueling trucks. Some trucks are large volume transports, carrying 7,000 up to 12,000 gallons of propane autogas. Smaller local delivery trucks, sometimes called “tank wagons” or “bobtails” carry 1,000 to 5,000 gallons of liquid propane. Typically, the greater the volume that is purchased over time, the lower the resulting per gallon price that is offered by the fuel retailer. Retail fuelers /marketers purchase large volumes of fuel from propane production companies. Propane is trucked or piped from the production facilities to above ground and below ground storage areas. Like LNG, there are centralized storage facilities that may be tied via pipeline and/or truck lines to move propane from points of production to intermediate storage. From the intermediate storage, trucks are commonly used to refill storage tanks at vehicle filling points.
Propane autogas is volatile and easily vaporized. For converted existing gasoline spark ignited engines, propane is typically injected into the engine as a vapor, but is kept as a liquid up until it is near the engine. In newer propane engines, the propane is injected into the engine as a liquid, improving its combustibility.
Propane fueling systems consist of a tank, transfer system, controls and dispenser. The fueling system is all liquid based, and like LNG, the liquid propane will gasify under lower pressures and higher temperatures. The tanks are typically pressurized from 50 to 265 psig. At atmospheric pressure, propane’s boiling point is -44°F (-42°C). In order to keep the fuel as a liquid in storage tank, the tank is pressurized, which raises the boiling point. For example, at 130 psig, propane boils at about 70°F (21°C) and at 200 psig, it boils at 100 °F (38 °C). In the engine or just upstream of the engine, as soon as the liquid pressure is reduced, the liquid changes to a gas.
 Air Liquide Gas Encyclopedia, “Propane” http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=53 , retrieved July 2, 2014