Aviation fuel is essentially paraffin, you can't add very much of that to diesel without also adding some lubricant, certainly not on modern engines anyway or mechanical damage is likely.

The thermal efficiency of diesel engines is considerably better than petrol, that is one reason for there improved economy, related to that is the fact that they will run on a very weak mixture, the fuel input only being controlled by the throttle position with a full charge of air on every stroke, EGR systems aside, most petrol engines require a constant fuel air ratio. Diesels will reward you much more for using a light throttle.

Edited by Peter.N. on 28/10/2011 at 14:02

"The only reason that diesel is more efficient than petrol is to do with the mass of the product not the density or volume.Diesel has considerable more mass than petrol and so contains more energy."

I think what you are trying to say here is that diesel has a higher relative density than gasoline!

What is often overlooked when comparing diesel engine efficiency with that of gasoline engines, apart from the advantage of the greater calorific value of diesel fuel is that pumping losses (moving the gases around above and below the piston) and engine internal friction increase as the square of engine RPM- deliver the power at a lower RPM and you waste less fuel just keeping the engine turning, hence the modern diesel is at present more economical.