A true flex fuel idea/question

Would it be possible to make an engine moderately efficient, and allowing it to use all the fuels that are available, gas, e85, diesel, etc, if you controlled how much air was sucked in to be compressed?

So, take a diesel and have a variable valve set up to open, or close at the right times to account for volume in a cyl.

Not that I am right, but I think it could work because if you only allow a certain amount in it would only be able to compress so much or little to essentially have the right compression.

Coupled with electronic injectors(or electrically controlled) you could supply the right amount of fuel for the proper air charge too.

The things I do know and have read are diesels use glow plugs, direct injection, and have high compression. Gasoline is low compression, have either direct, or port injection, and use spark plugs. So it would have to be a dual plug setup if it were to have a chance.


This is just a complete theoretical thing. I'm not concerned with money or how complex it may be to make, just an open discussion. So any and all constructive criticism is good and allowed.

And if I put this is the wrong forum and someone is able to move it to more appropriate forum, thanks. And sorry.

You would have to change the piston height each time you switched over to diesel plus have it somehow upgradable so the compression could be bumped up from 160 to a couple hundred psi. It won't happen. With diesels they use no spark plugs. The air and fuel is compressed until it explodes. It's a controlled explosion. Gas gets lit off with a spark. Mixing the two on a motor will blow it up. You could set a car up to run pump, E85, pump + meth, race gas, etc.

I do mean a separate fuel at a time. Just it would need two types of plugs for the difference in ignition.

While they are only small engines, some diesel tractors have a decompression lever to allow the motor to speed up because lack of compression. That's why I was wondering if you could control compression with valve timing.

I'm sorry but I don't see how valve timing or anything can make a 9:1 motor turn into a 20:1 compression ratio an average diesel uses. That is such a huge change. Maybe there's already something out there like it. I see no point to doing it. That's a huge engineering nightmare to figure out. If the main draw is mostly to be more efficient it would be better off figuring out how to design an engine to lose less heat to its surroundings from the combustion events. That's the key ticket to better mpg. An engine right now is only using about 25% of the energy from the fuel because the rest is lost as heat. I bet many have already figured it out but the EPA, government, or oil companies have kept them quiet because the petrol industry is such a huge business.