I have only a general understanding of engines but I think a diesel has a much larger compression ratio than a gasoline engine.

Multi-fuel engines do exist and have existed for quite some time, though I do not know much about them. The military often uses them in vehicles, but I believe the advantage lies in battlefield convenience more so than engergy efficiency. I think you get a more efficient engine with a highly refined design for a single fuel (design refined for the task, commuter vehicle vs. cargo truck), coupled with conservative driving habits, than with the ability to buy and burn whatever fuel is cheapest at the moment.

Good thinking though.

Flexible fuel engines also exist. They can be designed as gasoline/natural gas hybrids or gasoline/ethanol hybrids. Also, gasoline/electric hybrids and diesel/electric hybrids that can be plugged into the power grid effectively run on whatever is being used to produce the current marginal electricity production. In southern California, I believe this is natural gas. Biodiesel and diesel fuel can both run in a diesel engine. I believe the only modification necessary is to preheat the incoming fuel a little bit to compensate for biodiesel's cold-weather performance. Specially modified diesel vehicles can run straight vegetable oil (SVO) or waste vegetable oil (WVO), but I am not sure what the modifications are that allow this. More information is available at the biodiesel web sites. I don't think any of these engines run two fuels simultaneously, but they can be capable of switching fuels on the fly, which I think is just as useful.

Like what others have said, flexible fuel vehicles can be made. However, doing so saps efficiency. Much of your savings can be lost if, for example a gasoline only engine gets 30mpg, while the flex vehicle that can also burn diesel only gets 23mpg. Ethanol/Gasoline is close enough that only timing has to be changed between, however, a car designed solely for the ultra-high octane fuel that is ethanhol would be more efficient at burning it than one that can also burn regular.

I see what you are saying about the benefits of being able to switch fuels, and I'm all for it. But the idea of having each cylinder running a different fuel is a bit convoluted. That would definatly be a product of overengineering, and way to complex to deliver any savings on the ablity to use your choice of fuels.

I don't think it would be possible to make a diesel engine work with gasoline because the high compression would cause the gasoline to explode upon injection (which is very very very bad for an engine).

I like what your saying. The idea of having flexability in fuel is a good idea. The most efficent form of fuel would be hydrogen as all fuel is based on its content. In which case water can be used as fuel. Once broke down you could use the hydrogen from it to run your vehicle regardless the type of ICE you have. Specific inventor would be Stan Meyers who designed the Water Fuel Cell (WFC). that could be hooked up to almost any vehicle and run. Although he was assasinated he made many patents that can be found free by searching them on the web even videos on youtube.com. I am currently trying to reproduce his invention. I plan to assemble it over the summer and install it on my old beater to test it out. There are many designs based on what he has done which can be duplicated. I suggest that you check them out and see for yourself. It all is based on the idea as hydrogen as a fuel.

I didnt realise that Stan Meyers had been assassinated.Maybe his idea works and the oil companies decided to take him out. I think water vapour is also a greenhouse gas which is what is produced when you burn hydrogen in an internal combustion engine so they may have to add that in to their climate change model if people start using it in their cars. I just made my first batch of home brew biodiesel and it seems to work ok in my car though it's not cost effective to make in small quantities as they charge a lot for small bottles of the methanol that you need to make it. Cost comes way down if you buy a large drum of methanol and get some used oil from a restaurant. I read recently that they are working on a device which makes fuel by converting the CO2 in the atmosphere back into hydrocarbons.

Stan Meyers alleged that he was offered a "billion dollars" for his "water cell;" this is the true inventor's dream. That's far more money than he could ever have made had he marketed his invention. There are two possibilities:

1.) It didn't work, or

2.) there was never any "billion dollar offer."

He wasn't assassinated, he suffered a cerebral thrombosis after eating a meal at a restaurant.