Fuel Preheater theory and application

[overdrivegear]

I added a fuel preheater to get the #2 diesel hot so it will atomize better through the nozzle.  I have a counterflow plate heat exchanger that get the fluid up to around 140 F.  Because of temperature-viscosity relationship, this should have a big effect on injection performance, but I can't really quantify it other than, "Yeah, it's still running".  Anyone ever done this or know a way to test results?

Oh yeah, I was looking for that awesome thread on the VE Injection Pump rebuild and couldn't find it in the search feature.  It's the one that originally started in the French section and has all of those excellent pictures of putting it back together...

[Rabbit on Roids]

if you've ever felt the temperature of the fuel coming out of the pump, its warm. way warmer than body temperature. and this was on a cold day, it was about 30* outside. so i really dont know if your fuel heater is really going to help that much, but it will help heat the fuel up faster than the injection pump. my car will heat a full tank of fuel (15 gallons) and heat it up pretty darn quick.

[jtanguay]

according to some info i found on the net, 150F-160F is the proper range for diesel atomization.

taking fuel temp readings from the return line is the best idea.  i'm not too big of a fan of a heat exchanger idea to heat the fuel, as it may heat the fuel a bit too much.

the newer TDI's sometimes see fuel temperatures in excess of 90C, in which the computer actually retards the timing, and reduces fuel quantity.  you'd want to make sure you keep the fuel below 80C if you can.  but ideally you'd want it between 65C and 70C.  the problem is that regulating fuel temp within a 5 degree window isn't an easy task... especially with variables like fuel flow, outside temp, etc.  i'm working on something that will be able to do all of that though  :wink:  another benefit of heating the fuel is less NOx emissions.  i wish i had a diesel pop tester to play around with different fuel temps.  :lol: and mess around with some veg oils as well!

engines that could really benefit from fuel cooling would be the PD and CR types.  their high injection pressures create a large amount of heat...

[clbanman]

Jtanguay, I believe the number you are quoting comes from some of the patent applications for diesel heaters, am I correct?   I spoke with our MTU tech about diesel temps, and he said ideal temperatures should be in the 90-95 degree F range in his opinion.  I know we install fuel coolers on our trucks or the fuel gets too hot.  The only units we install fuel heaters on are those going to areas like Siberia, Khazakstan, or Fort McMurray in Alberta.

Calvin

[jtanguay]

Jtanguay, I believe the number you are quoting comes from some of the patent applications for diesel heaters, am I correct?   I spoke with our MTU tech about diesel temps, and he said ideal temperatures should be in the 90-95 degree range in his opinion.  I know we install fuel coolers on our trucks or the fuel gets too hot.  The only units we install fuel heaters on are those going to areas like Siberia, Khazakstan, or Fort McMurray in Alberta.

Calvin

90-95C? woah!!! considering the TDI's really start reducing injection timing and fuel quantity at that point.  good to know though.  unless that is in deg. F.

the reason i would install a fuel heater is so that during the first 5-10 minutes of run time the injection pump and injectors could really benefit from warmer fuel.  poor emissions & running situations could be avoided.  it must take quite a while for the fuel to reach 90-95C even in places other than Siberia...

i think everyone will agree that really cold fuel makes their car run weird, and too hot fuel can also make the car run weird.  but there is a sweet spot somewhere in between, that their diesel runs at its best.  the beauty of a unit that can both heat and cool the fuel is that it is truly universal for every diesel application, regardless of climate.  VW would probably never install something like this due to the added cost, even though it would be beneficial.



so at 194F (90C) look at where the timing would sit!  and the injection quantity would also be lower as well.  i've heard that if the fuel is too thin, it can even leak past certain parts in the injection pump, possibly the plunger?  so thats not good either.

[clbanman]

Edited post to clarify I was speaking of the Fahrenheit scale.
I do agree that there has to be a sweet spot and if we could find out for sure what it was we could look at solutions to try and keep it there.   I would think this would help performance, efficiency and longevity.  We had a filtration training seminar at work, and one of the things mentioned was that oils and fuels are created by chemists.  Each product is designed for a specific function within a specific temperature range.  An oil designed for proper lubrication at an operating temperature at 175 degrees F is not going to do the same job at 30 degrees F.   For fuel as you mentioned, the viscosity changes affect the ideal timing.

Calvin

[jtanguay]

32deg C isn't too bad.  i'd like to do my own little tests to see which is best.  i bet the type of fuel matters in this case as well.  winter fuel probably doesn't need to be 150-160F.

i've heard that running a cooler thermostat can affect engine wear...  and it makes sense because the oil would be cooler as well.

[clbanman]

Yes, if your oil temp doesn't get into the range it was designed for by the manufacturer, you will greatly increase engine wear.  We had a few engines that took out main bearings in less than 2000 hours due to the fact that the engine never got over 100 degrees F (coolant temp).   If the oil is too cold, it doesn't provide the lubrication that it is designed for.

[Hey]

When my pump gets very hot.. the idle tends to decrease. I also feel I have less performance.

I think ~20°C before the pump or so is the best. So I would say leave it be in winter and put a fuel cooler in summer.

my 2 cents

[blackdogvan]

FWIW I worked with a high performance catamaran imported from Australia a while back that ran E series 3406 Cats - 14L 6cyl 800hp. 45', 40 knot cruise @1800rpm, sweet ride too.

Anyway they had fuel coolers installed down there as the ambient air and water temps caused the fuel to warm up & reduce engine performance.