With nearly 200,000 propane autogas vehicles on U.S. roads today, the propane autogas technicians required to service these vehicles are already in high demand. With a significant projected growth in propane autogas vehicles by 2020, this need will grow exponentially in the coming years.

Converting a vehicle to propane autogas will add systems to, and in some cases remove systems and parts from, the original vehicle’s fueling system. It is critical for automotive technicians performing vehicle conversions to fully understand the conversion process, as well as the applicable safety codes and standards to assure the converted vehicle is reliable and safe for those who operate it.

Fuel System Types

Current propane autogas fuel systems are available in either bi-fuel, dedicated, or dual fuel configuration, where the vehicle’s original fueling system has been modified or replaced with specialized components to allow for the use of propane autogas as a fuel source.

A bi-fuel propane autogas vehicle refers to a gasoline vehicle that has been converted to run on propane autogas or gasoline (one or the other). The switching between fuels can take place automatically based on fuel tank levels or through a manual switch operated by the driver. By using the two fuels on board, a vehicle’s driving range can be extended into areas where propane autogas refueling facilities are not readily available.

A dedicated propane autogas vehicle refers to a vehicle that operates solely on propane autogas through the replacement of the vehicle’s gasoline components with a fully integrated propane autogas fueling system.

Dual fuel autogas systems are currently offered primarily for heavy-duty vehicle applications. This system mixes a percentage of propane autogas into the diesel fuel on a conventional compression-ignited diesel engine.

Differences in Propane Autogas Fuel-Injection Systems

Propane autogas vehicles operate much like conventional gasoline and diesel vehicles, as both use spark-ignited (gasoline) or compression-ignited (diesel) engines. The three most frequently used types of propane autogas fuel-injection systems available are (1) vapor fuel-injection, (2) liquid fuel-injection, and (3) direct fuel-injection. In all three types, propane autogas is stored as a liquid in a relatively low-pressure tank (about 300 psi). However, since the different fueling system components for each of these three different delivery methods are designed and optimized for one purpose, the components are seldom interchangeable. The following will provide a brief overview discussing the differences between these three fuel delivery methods.

Vapor Fuel-Injection System

Propane autogas travels from the fuel tank through the fuel line in a liquid state to the fuel regulator, where the regulator reduces the propane autogas from a liquid to a high-pressure vapor. The vapor pressure is precisely controlled by the regulator for optimal combustion. Moving out of the regulator, the fuel vapor travels to the fuel injectors and into the intake manifold and combustion chamber for ignition.


Liquid Fuel-Injection System

A liquid fuel-injected system works in much the same way as a vapor fuel-injection system, except that the liquid propane autogas is not converted to a gaseous state in a regulator. Instead, the fuel is delivered into the combustion chamber in a liquid form through a specialized fuel injector. This way, the fuel combusts more fully and provides optimal power and throttle response. When injected in a liquid state, the fuel displaces significantly less air in the engine and lowers the temperature of the air charge, increasing its density. Because propane autogas does not occupy a significant amount of volume within the intake, the performance of the engine will not be reduced. Furthermore, the fuel will vaporize as it mixes with the air, absorbing energy, lowering the air’s temperature, and ultimately increasing its density, again increasing performance.

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Direct Fuel-Injection System

A patented fuel delivery system for propane autogas vehicles is the propane autogas direct-injection system. This technology injects propane autogas directly into the combustion chamber of the engine at a very high-pressure. Developed and patented by ICOM, this system uses the vehicle’s original gasoline high-pressure pump and fuel injectors to deliver liquid propane autogas directly to the combustion chamber, eliminating the need for modifying the fuel rail through the addition or substitution of propane autogas-specific injectors.

NAFTC Propane Autogas Vehicle Technician Training

In support of the growing propane autogas vehicle market, the National Alternative Fuels Training Consortium (NAFTC) has launched a new _Propane Autogas Vehicle Technician Training _course funded by the Propane Education & Research Council (PERC).

Participants in the Propane Autogas Vehicle Technician Training will learn how to convert vehicles to run on propane autogas and how to service these vehicles safely, understand the theory of operation and ability to diagnose and repair vapor, liquid, and direct injected LPG systems.

The 3-day Propane Autogas Vehicle Technician Training class is available at the NAFTC headquarters in Morgantown, West Virginia, as well as other nationwide locations. Currently scheduled for April 12-14 at the NAFTC headquarters, this new technician training is available as a “train-the-trainer” offering as well as an end-user technician session. More information, including where and when the training will be conducted, can be obtained by calling 304-293-7882 or visiting or

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