The main point with Flexible Fuel Vehicles is that they can change their fuels according to fuel availability and cost. Suppose you run a fleet company, and all your big trucks run on gasoline. If gasoline is unavailable then you go bankrupt, but if you can switch to another fuel then you're okay, even if the compression ratios aren't perfectly optimized.

Presently, I think that two different engines have the edge: one that can burn either gasoline or ethanol, and the second that can burn either diesel or vegetable oil. The reason is that the storage tanks for these fuels are very lightweight. If you instead want to fuel your vehicle with hydrogen, Borax, propane, or natural gas, you are looking at fuel tanks with between 7 wt% and 11 wt% storage capacity. Such a heavy tank will increase the energy expenditure to get the vehicle up to speed, compromise acceleration & handling, and drastically reduce range. Featherweight fuel tanks are what give ethanol and biodiesel the edge.

Internal combustion engines are inexpensive, but they require mechanical systems to drive the car, including drive train, axles, transmission, steering & braking linkages. All these components add to the weight of the vehicle. In contrast fuel cells are expensive, but they facilitate electric drive. If each wheel has an electric motor, then you can do away with the mechanical drive train, transmission, axels, steering and braking components and save alot of weight. The fuel cell alone is twice as energy efficient as an internal combustion engine, but when you combine that efficiency with the extraordinary weight savings of having no mechanical components (except wheels and suspension) then the amount of fuel you need to run the car may be reduced to a thimblefull.

If someone can develop a fuel cell that can generate electricity with the same efficiency using either gasoline or ethanol, then all the benefits listed above can be realized:

- make full use of traditional refueling infrastructure
- use different fuel depending on availability and price
- smooth transition to renewable fuel
- featherweight onboard fuel tanks
- double energy efficiency of internal combustion engine
- eliminate heavy mechanical components
- lower maintenance
- longer vehicle operating life
- super-lightweight vehicle construction possible
- fewer materials used in construction
- easier recycling
- super-low rolling resistance due to lightweight chassis
- extra interior volume
- more room for safety features
- more stylish vehicle designs
- more aerodynamic vehicle design
- quieter vehicle operation

Opinions ?