Mechanics of Conversion
With few modifications to the engine, virtually any gasoline engine can be converted to run on propane. Vehicles can be equipped to operate solely on propane (dedicated conversion) or to switch between propane and gasoline (dual-fuel conversion). Propane tanks fit compactly into car trunks. In trucks and vans, propane tanks replace gasoline tanks and fit under the body of the vehicle.
Propane is stored as a liquid, usually in one tank, at pressures dependent upon the ambient air temperature (e.g. at 70° F, the pressure of propane would be 127 psi; at 100° F, the pressure would be 196 psi). In a propane engine, the liquid travels from the tank to a vaporizer/pressure regulator (also called a converter), which converts the liquefied propane to a gaseous form. From the converter, the vapor goes to an air/fuel mixing device where it is mixed with filtered intake air before being fed to the engine on demand. As the fuel/air mixture is completely gaseous, the cold start problems associated with liquid fuels are eliminated.
A complete conversion system includes the fuel controller, valves, actuators, electronics and software needed to convert a vehicle to propane operation. Conversion systems can be of two types:
Open loop system: This system does not contain control electronics and no feedback is provided to the controller on how well it is performing. The controller uses prior calibrations to determine what to do.
Closed loop system: This system incorporates an electronic sensor that provides continuous feedback to the fuel controller on how well it is performing, thus "closing the feedback loop." Closed-loop conversions are generally more expensive than open-loop systems.
When considering a vehicle conversion, it is important to estimate the investment payback, which depends on:
Number of miles a vehicle travels in a year
Original fuel economy of the vehicle
Initial cost of the conversion
Vehicle resale value after conversion
Part of the cost may be deducted from federal taxable income. Check with your state for information about the availability of state and local tax incentives.
Please check with your vehicle manfacturer for conversion estimates. Please click here for a list of manfacturers of After Market conversion kits.
Aftermath of Conversion
Some effects that can result from converting a vehicle to run on propane fuel are as follows:
Conversion components (fuel tank, etc.) add weight to the vehicle and therefore, may slightly increase the consumption of fuel per mile. Propane costs for fleet vehicles typically range from 5-30 percent less than conventional or reformulated gasoline, so the cost of increased fuel usage can be recovered over time. Also, many states offer fuel tax incentives to encourage the use of clean fuels, thus further reducing the operating costs of the vehicle.
Converted vehicles perform very much the same as gasoline vehicles. The most significant difference a driver may notice is a slight power loss. Propane use may result in power loss of up to 7 percent. However, power and performance can be optimized through engine adjustments of the air/fuel mixture, ignition timing, and the compression ratio. Excessive loss of power, however, may indicate improper installation or tuning of the conversion system. On conversions, it is important to follow the kit manufacturer's instructions on how and when to tune a converted vehicle.
Many conversion kit manufacturers provide warranties for their parts, and certain states have laws requiring that aftermarket kits be warranted (e.g. the California Air Resources Board requires that the manufacturers of alternative fuel retrofit systems warrant their systems to certain workmanship and materials specifications similar to a new car warranty).
Before converting any vehicle, it is important to know the kind of warranty that the conversion kit manufacturer offers. In addition, the fleet operator should seek answers to the following questions:
Would the propane conversion void an original vehicle manufacturer's warranty?
Are those failures caused by the conversion system covered under the vehicle warranty?
If the conversion kit or parts of the kit fail or cause another part of the vehicle to malfunction, would the cost of the repair and any related damage be covered by the kit manufacturer's or installer's warranty?