HOW MUCH HEAT TRANSFERS TO FUEL?

[Ian Anderson]

Following on from another thread discussing swirl pots and fuel systems it is apparant that fuel tends to heat up in an EFi fuel rail and this in turn can heat up the fuel in the swirl pot or even the main thank.

How much heat is transferred?
What is the difference in inlet vs outlet fuel temp?

Lastly should a radiotor system be fitted to cool the return fuel (between the rail and theswirl pot / main tank)?

Reason I ask is that on the GT40 I have 2 35 litre tanks and have found they do get warm (from 1/2 tank down) and also we have a person about to go racing and surely cold fuel will make a better power

Any thoughts

Ian

[ian.stewart]

Cold fuel is allways better to cool the air/fuel charge, and so is cool air for the same reason, The heat not only comes from the fuel circulating thru the fuel rails but also from the pump which is fuel cooled, and heat is generated when anything is pressurised, I have never seen a rad fitted in a fuel line before, It may work, I know Smokey Yunnik used to cool his fuel in the 60s to get more fuel into the tank as the fuel contracts when cooled and may well of had an advantage in being cool in other places, Drag racers and LSR cars often use Cool cans, cans packed with dry ice to cool the fuel and air intake temps, that may help your mate but check the regs first before he tries this, the Blue Book is normally quite specific about this sort of thing.
Air conditioning is often overlooked as a charge cooler, I dont think there is any gain from doing this constantly, [Free HP dosent exist] but Ford use a similar system for their big supercharged truck, circulating cold air over an intercooler that is controled by a switch, hit the button and you get 55hp?? more for about 30 secs before the cooling runs out, I think it takes another 10 mins for the cooler to recharge its self before it can be used again.
Ian

[Coops]

one of the vehicles i work on at work (Citroen Dispatch 2.0i turbo diesel) has a fuel cooler mounted under the body, it looks like a small alloy radiator (about the size of a standard size oil cooler) this has an air scoop mounted to it to direct air through the radiator, i think this is on the return fuel line to the tank,

[GreenV8S]

I understand that TVR used the air conditioning cooler to cool the fuel return on some vehicles. I've seen oil coolers used for that too. You'd probably need to insulate the fuel lines and tank from exhaust heat to get any great benefit. My fuel rail is lagged to reduce heat soak and prevent hot starting problems, but the fuel still gets very hot when it's running because the air down the tunnel dumps loads of heat from the exhaust and transmission straight onto the fuel tank.

[stevieturbo]

A radiator is a radiator.

I have an oil cooler mounted in my return line to cool the fuel. I just got it with -6 fittings.

Its not mounted in an ideal position though, under the car with a little duct/fins, but every little helps. I did this after Retro in July, as when driving down the motorway in the hot weather etc, my fuel tank was getting very warm, and the pumps didnt sound too nice either !!!
Havent really used the car much in such warm weather since though, but so far, the pumps havent sounded as bad with the cooler in place.

Ive seen a few cars running fuel coolers.

[stevieturbo]

one of the vehicles i work on at work (Citroen Dispatch 2.0i turbo diesel) has a fuel cooler mounted under the body, it looks like a small alloy radiator (about the size of a standard size oil cooler) this has an air scoop mounted to it to direct air through the radiator, i think this is on the return fuel line to the tank,

Seems quite common on modern diesels.

Ive seen a nice 8mm hosetail style cooler on a BMW 4cyl diesel, VW's with a cooler mounted under the floor. Strange looking thing, not really in any airflow either.

[Coops]

i may enquire how much this cooler is and the duct, and use it on my car on the return line then

[ihatesissycars]

Alot of Vauxhalls are fitted with a fuel cooler now. Corsa have had them the longest i believe.

[racer]

How much heat is transferred?
Any thoughts
Ian

The heat does rise.. On the EFI models it is constantly circulating from rail to tank and back. When there is no movement/air to cool the rail, this can become a problem for the earlier EFI models as it leads to fuel vaporization.

It is NOT a factor on your fueling system (hotwire) as you have a fuel temperature sensor that, when is working, provides that data to the ECU which adjusts for the fuel heat.

On the nother hand, when that fuel temperature sensor goes (and they do), you will have a hard time running the car at idle when hot. It will stall when you go into slow traffic.

racer

[Ian Anderson]

Racer

That is good to know but I am sitting between 2 fuel tank in the 40 and would rather the fuel was not heating thus causing mor vapourisation and potential for a fire.

On another forum someone suggested moving the fuel regulator close to the HP pump and blocking off the end of the fuel rail. The fuel regulator is to be fitted in a T in the fuel line from the HP pump. On that basis the whole fuel line remains pressurised to Fuel rail to regulated pressure, but only the fuel that is being burnt moves through the rail. Again the overflow from the regulator is put back to swirl / tank.

Has anyone used that on a Rover setup?

Thanks
Ian

[GreenV8S]

That sounds like a bad step backwards. Without the flow through the fuel rail this will run a lot hotter and you're likely to suffer far more evaporation problems. It may mean the tank itself runs hotter (although it may not, because the fuel rail isn't the only source of heat) but I think it would cause more problems than it solves. The fuel rail is easy enough to insulate, if heat input here is a problem.

[stevieturbo]

Dead end systems are stupid IMO.

[ian.stewart]

As Stevie says not a good idea IMO, If the pump picks up some air, the only place for it to go is to the injectors, enough air at high revs could cause the demise of your pistons., I know there is a swirl pot in the system, but even swirl pots are fallable.

[GreenV8S]

Dead end systems are stupid IMO.

They seem to be getting more common on modern production petrol engines, is that just to reduce cost?

[stevieturbo]

Dead end systems are stupid IMO.

They seem to be getting more common on modern production petrol engines, is that just to reduce cost?

I would guess so. I cant see any performance reasons for doing so.