Differences between Dual Fuel Systems and Bi Fuel Systems
Bi-fueled vehicles, by definition have two entirely independent fuel systems that can switched between each other. The almost universal Bi-fuel system is a gas and CNG (compressed Natural Gas) system, with kits for conversion from a gasoline fueled to a gas and CNG car are becoming popular in Europe. Adding CNG as a fuel is a relatively low cost upgrade. Essentially the upgrade is the added tank, the line from the tank and a variable valve to regulate how much gas is released, the valve can either be regulated by electronic means or even a simple mechanical hook up to the accelerator.
Duel Fuel Vehicles are a more broad group, they include Flex fuel where there is just one tank that you can add either in any proportion and the car figures it out and other technologies like Diesel enhanced CNG, where up to 10% diesel fuel is injected along with the propane into a diesel engine.
Diesel is first the name of a technology, not a fuel. In fact, Dr. Rudolf Diesel invented the engine, way back around 1892 to run on a wide array of fuels, including rapeseed and hemp oils, straight, not even converted to a "bio diesel". This is important to note, because over a hundred years ago, flexible fueling was considered, a viable technology was developed , but the fuel supply was monopolized by petroleum companies, diesel developed into a singular "fuel" instead of the concept of escaping the single fuel source.
