Fuel Injection Fuel Cooler / Radiator

[Ian Anderson]

I have noticed that the returm line from the fuel rail gets warm (heat soak in the rail) this goes back to the swirl pot that is constantly refreshed from the tank (cross over valves yada yada yada)

Question is that - is it advisable to fit a fuel cooler / radiator in the return from the fuel rail? Presumably cold fuel is better than hot?

I have heard that a lot of standard road going cars now have these fitted as standard to stop the whole fuel system heating up. I am led to believe these are normally mounted low down with a scoop to duct air into it and said to be used also to dissapate the heat generated by the HP pump.

So if a road car with say a 60 liter tank needs a cooler (1.6 litre engine returning reasonably small flow into a big volume) what hope of a 40 with 2 small tanks of 35 litres each?

Does anyone have fuel heating problems that is running EFI? If so how do you / did you plam on rectifying the problem?

Thanks
Ian

 

[JohnC]

When I was at Caterpillar, we used to regularly see only 90% of the engines' rated power on our dyno after the diesel fuel had heated up. Fuel coolers helped our situation because we had no alternative - our diesel fuel pumps were mechanical.

On fuel injected gasoline cars, the OEM's run the electric fuel pump at reduced voltage when the engine is at low load to keep from circulating (heating) excessive amounts of fuel. On my car I run the fuel pump at about 9 volts (via a PWM controller) when I'm at idle and low manifold pressure, then I bump it to 12v for low boost (<10psi), then I bump it up to 16v for high boost (10psi and above)

Kenne Bell have some interesting reading on their site about the fuel heating problem, and some very good reasons why people should not grossly oversize their fuel delivery system:

Kenne Bell Boost-A-Pump

 

[Jim Cowden]

Ian

A few manufacturers are now using a non return on the engine.
That is the fuel rail has a supply only.
The reg is in the tank or external for that matter ,the pump supplies the reg ,it sends fuel on to the engine at the required pressure and the reg bleeds of to the tank hense the fuel never gets hot as it is not curculating to the hot engine.
Manufacturers are using it as it gives better fuel economy apparently.

I do not know what effect on the base tune settings it would have if any. (mixtures)
and would have to be checked.

I know someone who has tried this and found it worked well with no ill effects.
His surge runs at room temp.
I to am going to use it as it makes sense.

If you dont want to do that you can send the fuel from your returns back to the tanks and not the surge.
But you will have to make sure your supply pumps are capable of out running your main as often the surge tank relies on the return to keep it full.

Jim


Jim

 

[Ian Anderson]

Jim

This type of system was discussed on this forum in the middle of last year if memory serves me right.

On a 40 it would still mean a swirl pot as the HP pump would run dry in a standard tank under braking.

I also have been led to believe the fuel going through a HP pump also increases in temperature considerably due to the effect of the vanes etc. - Eventually you would be sitting next to a tank of hot fuel!

Also I could not figure out how any air would get out the system without any "dying" of the engine as the bubble goes through the injector..

Cheers
Ian

 

[Pete]

I believe when fuel is warmed up it atomizes easier staying suspened in air thus being burned more completely. That is why you saw radiator water preheating carbs before fuel injection. I don't know if or how much of a difference it would make when running fuel injection though.

Pete

 

[Jim Cowden]

Ian
I did not say remove the swirl pot.
You would still run a lift and a main pump.

Fuel is still going through the hp pump regardless so an amount of heat will be generated in either system.
The non return system still runs the same pressure as a return system and is still returning via a reg so it will not generate anymore heat via the pump itself.
The difference being that if it returns from the fuel rail it has time to heat the fuel due to engine heat soak.
The fuel will have to get hotter due to this reason.
On the dyno I have experianced surge tanks that you can not touch as they are to hot.

I would say this is why the manufacturers are moving towards the non return system.
As the density of the fuel is lower and allows for more space in the combustion chamber for air thus making more power with less throttle.

As far as air bubbles they get bleed out by the injectors on inital start up from fueling up.
When the engine is turned off the injectors and the check valve in the pump will hold line pressure keeping the fuel under pressure and raising the boiling point to not allow fuel to boil off as per a normal fuel inj system.

When I do my system I am more than happy to post on the outcome
Im more than happy to be the guinea pig

Economan
I agree with you on the heating of the fuel on a carby as the fuel has further to travel heating it will make it lighter I would think allowing it to get to its destination without falling out of suspension as it is relying on air speed only to move it not pressure.
Also I think they are trying to avoid icing of the throttle due to the low pressure at the throttle area.

 

[CliffBeer]

I believe when fuel is warmed up it atomizes easier staying suspened in air thus being burned more completely. That is why you saw radiator water preheating carbs before fuel injection. I don't know if or how much of a difference it would make when running fuel injection though.

Pete

Pete,

Yes, that's true, atomization is improved (to a point) with higher temperatures, however, a more dense charge of fuel and oxigen can be packed into a cooler intake charge (producing greater hp), hence, intercoolers for turbochargers which notoriously elevate intake temperatures.

There are other problems associated with fuel temps which are too high such as vapor lock. This is a big problem for some cars in some countries where under-hood temps get so high that the fuel actually vaporizes in the carb body or fuel lines.

 

[Sandy]

Another area for improvement is to controll the flow of fuel to the rails. At idle your 1000hp efi pump is just pumping up the return line with the bulk of it's fuel. The idea is to better control the fuel pump more in line with the engines needs so less fuel ends up being circulated. In a non return system it likely would be just the pump heat, in a return system it would be a good amount of heat from the rails and pump. Right size the pump will also help.

Some of the simple fuel pump controllers can do this to some extent, they control the fuel pumps speed related to some engine rpm point. The few that I looked at seem very simple, i.e., they have a set point rpm, and below that they operate the pump at a slower speed, and above that they roll the pump at 100%.

I'm working on a simple AVR based (microprocessor) that allow a fuel pump curve based on engine RPM with a couple of break points for different rpm settings. It's still pretty dumb as it based on RPM and Battery voltage only but will do better then one breakpoint like the others I have seen support. I'll post some info after I get a proto working (Also use as a shift light, fan control etc). Aeromotive has a new one that has more control now, but I have only seen a couple of pics of it. Some just have a control that lets the user just set the pump at the max flow that will be needed and all done (Weldon's dial-a-flow pump controller). I'm sure some of the EFI boxes can also do justice to setting the pump flow since they have all the parameters needed already instrumented.

All that being said I would be very interested to see how the non-return sytem works out. Would make life much easier as for the dual tank issues that arise when using EFI (or carbs with bypass regs) in the GT40s.

Sandy