Fuel heater- Good or bad idea?

[EcoCivic]

I was thinking about how fuel temperature affects MPG and power. I came up with the idea of heating the fuel rail on a returnless system with engine coolant to possibly help the fuel vaporize more completely. If that would work, what would the ideal temp be? I don't really see a disadvantage to heating the fuel besides maybe making knock slightly more likely, but I do not know that it would help either. What do you think?

[Stubby79]

Dunno how much benefit it would be on a modern engine...the injectors on newish engines spray against the intake valve, which, being warm/hot, helps evaporate the fuel. (I think!)

Direct injection? Even less likely to help.

[t vago]

I guess it'd work... Maybe. Look, let's do a thought experiment:

Take some fuel and heat it up to 90 C, which would be about the temperature of your coolant on a warmed-up engine. Now, spray it into your intake manifold, which probably has air at around 35 C, on a good summer day. Keep in mind that there has to be a 14.7:1 air/fuel ratio by mass, that fuel has about a 2.22 kJ/(kg*K) heat of enthalpy, and that air has about a 1.01 kJ/(kg*K) heat of enthalpy. Do the basic heat capacity equations, and you will find that:

The resultant fuel/air mixture will have a final temperature of 42 C, and that's assuming complete and total vaporization of the fuel as it gets sprayed out of the fuel injectors.

You'd be better off heating up your air.

[cRiPpLe_rOoStEr]

I'm aware that some flexfuel cars have electrically-heated fuel rails as a cold starting aid. Including some Mexican-made ones exported to Brazil.

Originally Posted by Stubby79

Direct injection? Even less likely to help.

It could actually help, allowing to a more complete vaporising. Don't you remember the introduction of direct injection to spark-ignited engines have been pointed out to increase the formation of particulate matter on them? Then, with a more complete vaporising, this issue would become less frequent.

[oil pan 4]

I have seen people installed these fuel heaters, they noted 0 or next to 0 improvement.
Warm air intake is better.