Fuel System 59 Alternative Fuels Alternative fuels can be of several different types. There are vegetable based fuels, aviation fuel and recycled petroleum based fuels that are used in combustion engines. These are in general not compatible with modern heavy duty over-the-road diesel engines. The use of unauthorized fuels may compromise the levels of pollutants in the exhaust to the point where the engine does not meet the emission requirements. This would make the vehicle illegal to drive on public roads. DO NOT use any kind of alternative fuel unless specifically authorized by Volvo Trucks North America, Inc.