Quote:
Originally Posted by Christ
Bone: Heating fuel also reduces it's density, thus requiring more volume to obtain the same BTU output. This does greatly affect the scenario.
Ideally, you would change the viscosity of the fluid without changing it's density. (Adding water doesn't work for this reason, among others.)
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Its easy to compensate for a change in fuel density. Just add more fuel. Diesels do this when they switch from summer diesel to winter diesel since winter diesel has a lower btu content per volume.
Actually in a diesel engine changing the fuel temperature causes a big change in the compressibility of the fuel. This affects timing which has a bigger effect than volume of fuel.
A good reference on this type of experiment can be found in NACA-TN-565 on NASA's NTRS server.
They did find an improvement in efficiency but it wasn't 20%. The biggest change was when the temperature exceeded the boiling point of the fuel at TDC. Thus the fuel instantly vaporized upon entering the cylinder.