hot fuel vs. cold air

[EdKiefer]

Originally Posted by t vago

I did a little Excel heat energy calculation, using a specific heat of 1 kJ/(kg K) for air, and 2 kJ/(kg K) for gasoline. The air was assumed to be at 30 C (86 F), and the gasoline was assumed to be heated up to 90 C (194 F, and presumably heated up by engine coolant). A 14.7:1 mass ratio was assumed, too.

(1 kJ/(kg K)) * (14.7 parts air) * (30 C + 273.15 C) + (2 kJ/(kg K)) * (1 part gasoline) * (90 C + 273.15 C) =

(1 kJ/(kg K)) * (14.7 parts air) * (303.15 K) + (2 kJ/(kg K)) * (1 part gasoline) * (363.15 K) =

4456.305 kJ/kg + 726.3 kJ/kg =

5182.605 kJ/kg

Now, to find the final temperature of this mixture:

5182.605 kJ/kg / (1 kJ/(kg K)) * (14.7 parts air) + (2 kJ/(kg K)) * (1 part gasoline)) =

5182.605 kJ/kg / (16.7 kJ/(kg K)) =

310.3 K

or

37.2 C (98.9 F). This is a 12.9 F difference between the initial and final temperatures.

Given that my documented HAI gain of around 5% is done with an intake air difference of about 45 F, I would have to agree that 10% improvement with fuel heating seems rather unlikely.

Also on modern FI with return lines the fuel temp is far above ambient temps , my guess somewhere around 100 -140F range . the injectors get even hotter .
I would also wonder how heating fuel to 200F or so would affect long term reliability of injectors and even fuel pump as the fuel is used as a coolant .