Direct fuel injection engines definitely spray in liquid. Obviously it doesn't stay a liquid but I would say what it runs on is based on whatever gets fed into the piston, or any part that is directly a part of the engine. It isn't shocking though as you can run a gas engine on propane. I wouldn't do it with a modern one that has tight tolerances, but for most engine formats until its been optimized to the edge of breaking you can use propane.