MIT researchers come up with the idea of using E85 ethanol to prevent knocking when a gasoline engine is running at high temperature. As a result, a given size engine can produce about twice the power. Instead of keeping the size, a half-size engine would have the same performance of the comparable full-size engine, but an increased efficient resulting in a 30% reduction of fuel consumption.
Since ethanol is only used at a 5 to 100 ratio to petrol, ethanol would be filled once a few months. So effectively, it is like petrol-engine.
When I was still in Hong Kong (that's over 13 years ago), my standard petrol car has an "after-production" add-on water-injection which increased the efficient of my car by about 10 to 20% depending on driving condition.
The theory then was to use the water to increase the surface area of the petrol just before it is ignited by the spark-plug. The test at Hong Kong Polytechnics at the time demonstrated marked improvement in emission. That was the original result I installed the system.
Unfortunately, the water injection system failed only after working for about 2 years - due to the blockage of the injection needle and I was no mood to get it fixed. Anyway, the modification, though not working, did not create any noticeable performace degradation - just return to the original state. Quite remarkable!
I don't know how that technology is going now. Hope it is still alive and somebody is still improving it.