Hot Fuel in trucks for more power... what about US?

[shortysclimbin]

Well with all the recent talk about the KFC mod and other fuel mods I I would throw this my ideas for people to discuss.

In trucks the Diesel guys are pumping hotter fuel and seeing better numbers so why cant we? It makes since if you can fool the ecu not to retard the timing because of it. Also, in heating the fuel after the pump you can effectively raise the pressure in the lines.

I would say this should help atomization of fuel and may allow us to get better MPG, power, and lower egts... But I do not know how much.

So I open this idea for discussion... IF its worth someones time It wouldn't be that bad to machine some parts to do this.

 

[Gothmolly]

Hotter fuel is less dense right? This = bad, I thought, else why would the AT cars have fuel coolers?

 

[darkscout]

Hotter fuel is less dense right? This = bad, I thought, else why would the AT cars have fuel coolers?

Pre pump is bad, because the pump injects a certain volumetric quantity, so less dense.

Post-pump the amount of fuel is already chosen, heating it now will just increase the pressures (not sure by how much). Anyone know the thermal expansion coefficients of diesel? I can't imagine this doing anything significant.

 

[Azonic]

I am not sure your coolant would be warm enough..
I have never measured it..

But I can only imagine that with the PSI after the injector pump..
That STP laws would say that fuel is HOT..
And maybe hotter than your coolant, thus your idea may actually cool it down?

What is the temp of the fuel post pump? (I may be wrong so I want to learn!)

 

[GoFaster]

On a P-D, the fuel distribution leading to the injectors is in passages drilled into the cylinder head, and that operates at coolant temperature ...

 

[KERMA]

Yes, hotter fuel would help make more power IF the ECU didn't pull timing as the fuel got hotter. However, the injection pump is also lubricated by the fuel, adn hotter less dense fuel may not lubricate as well, so too hot is not good for the injection pump, and in fact may sieze the rotor in the head if it's too hot.

 

[darkscout]

Yes, hotter fuel would help make more power IF the ECU didn't pull timing as the fuel got hotter. However, the injection pump is also lubricated by the fuel, adn hotter less dense fuel may not lubricate as well, so too hot is not good for the injection pump, and in fact may sieze the rotor in the head if it's too hot.

However there's no temp gauge (that I saw) after the pump before the injectors. The injection pump is getting cold fuel, the suggested fuel heating comes after the pump gets it.

 

[DPM]

Not sure about PDs, but Peugeot HDIs measure fuel temperature using a probe in the return fuel flow, but attached to the common rail. Definitely sensing the fuel at it's hottest...

 

[alloutdoorsboy]

I was thinking of running a piece of diesel equipement on veggy oil and bought a set of injector line heaters that are electric. The guy selling them on ebay says they help atomize the veggy and you get more power with less smoke......I had wondered how it would work for diesel.

 

[Slave2school]

Wouldn't the energy needed from the alternator not offset the gains if you use an electric heater?

 

[EddyKilowatt]

On a P-D, the fuel distribution leading to the injectors is in passages drilled into the cylinder head, and that operates at coolant temperature ...

Even on the distributor-pump engines, my gut feel is that the fuel spends long enough going thru the injector (look at a cross-sectional diagram of one) to get pretty close to cylinder-head temp. Separately heating to coolant temp going into the injector probably wouldn't make much difference to the temp of the fuel spraying out of the injector... IMHO.

What's the boiling point for D2 at 20 bar pressure, anyway?

Eddy

p.s. Don't the WVO/SVO folks know a lot about fuel heating? They have to heat that grease a bit to get it to pump, and A LOT to get it to spray...

 

[BKmetz]

.

My opinion is that heating a thin fuel as D2 will have no noticeable real effect, a perceived positive HP effect, and a theoretical negative mileage effect.

If one takes the time to see what heating the fuel does to its viscosity, BTUs, and specific gravity, you should get lower fuel mileage. Here are some fuel oil tables I just happen to have.

.

 

[abctdi]

Hot fuel just seems so.o.o.o wrong...

 

[mojogoes]

Its the only way to go if you going to use bio with a high esta/fatty acid content , other wise it will still be solidified.

 

[shortysclimbin]

Ok so as stated above if the PDs do indeed cool/ warm the fuel with the head neither fully heating or cooling would be the answer... This would be one reason behind the PDs not running veg well at all.

Kerma, on the V6 TDI that comes in the passat the stock fuel filter has a fuel cooler/warmer on the top of it. It actually water cools the fuel before the pump. This may be a good alternative for those of us that need a little bit extra cooling. This unit also will fit in the stock fuel filter ring and only requires reworking the fuel lines and coolant lines a bit.

 

[KERMA]

Actually, I/we started working on something to try. Got a few ideas.
I didn't catch the "after the pump" part of this before. Might be something to it.

 

[Fix_Until_Broke]

.
My opinion is that heating a thin fuel as D2 will have no noticeable real effect, a perceived positive HP effect, and a theoretical negative mileage effect.

If one takes the time to see what heating the fuel does to its viscosity, BTUs, and specific gravity, you should get lower fuel mileage. Here are some fuel oil tables I just happen to have.....

It's about mass flow of the fuel, not volume (just like on the air side, more boost does not mean more air flow, just more restriction).

With hotter fuel you will have lower density, so more "volume" will have to go in to get the same mass in. This would create a theoretically longer injection duration. Mileage would theoretically increase (assuming the system is rejecting excess energy to the atmosphere via the coolant and radiator) because you would have to put less enegry in the fuel to get it up to self ignition temperature (beacuse you have heated it with some of that excess enegry that was going to the radiator).

The thermal expansion coefficient for diesel fuel is ~0.006 volume/volume*degree F.

The bulk modulus decreases as temeperature increases so it will take longer (more pump piston displacement) for the pump to build pressure in the injector line, so injection timing would change, but the system will automatically compensate for that (on the VE's anyway)

The temperature coming out of the injecton pump (to the injectors) won't be much higher than what's coming in because you have only done compressible work to the fuel from the injection pump(~0.5% volume per 1000 psi), however the injector return lines will be hottest since all the potential energy in the fuel has been turned into heat from injector leakage (~1 degree F per 145 psi) since no work has been done.

I would think that you definately do not want to increase the volume of the lines between the injection pump and the injectors (and if you do make sure it is symmetrical)

I'm not sure I understand the theoretical advantage of hot fuel - faster combustion is all I can think of. How much can we increase the temperature 100F max - will that be enough to make a difference?

 

[JLL]

Hot fuel bad

Hot fuel at the injectors is bad, it will cost you 1% power for every 10F increase in fuel temp. Its all about mass of fuel through the injector.
Maybe there is a way to make the ECU think the fuel is hot so it will compensate the injection by adding more fuel. You really do not want to make your fuel hot before the injectors.

And yes if you are fuel starved (no smoke at full power) chill the fuel for more mass flow. Cold fuel will also increase injection pressure and slightly advance timing.

 

[jackbombay]

Hot fuel is less dense so injection duration has to be increased to deliver the same mass of fuel, but that is also easily remidied with R520s which have such a short injection duration that the "start of injection timing" actually has to be retarded slightly in the software for them to run in their "happy zone".

So, the gains here are soley attributed to a decrease in ignition delay? Is there any other way hot fuel could add HP? Theoretically a quintupple dose of DFS would provide similar results, or would they?

 

[ToledoTDi]

Is it possible to increase the pump pressure? Would this not also have the effect of increasing temperature?

 

[darkscout]

Hot fuel is less dense so injection duration has to be increased to deliver the same mass of fuel, but that is also easily remidied with R520s which have such a short injection duration that the "start of injection timing" actually has to be retarded slightly in the software for them to run in their "happy zone".

So, the gains here are soley attributed to a decrease in ignition delay? Is there any other way hot fuel could add HP? Theoretically a quintupple dose of DFS would provide similar results, or would they?

True... But the pressure increases. The question is, does the pressure increase offset the reduced density?

(Completely random numbers)
15,000 psi at 1 g/L for .1 seconds of injection
or
20,000 psi at .9g/L for .1 seconds of injection.

Which one gets more fuel? Maybe it'll be more atomized, It's warmer AND at a higher pressure.

 

[Fix_Until_Broke]

True... But the pressure increases. The question is, does the pressure increase offset the reduced density?

(Completely random numbers)
15,000 psi at 1 g/L for .1 seconds of injection
or
20,000 psi at .9g/L for .1 seconds of injection.

Which one gets more fuel? Maybe it'll be more atomized, It's warmer AND at a higher pressure.

The short answer is yes

Density will go up with increased pressure/density will go down with increased temperature, but as I stated in my previous post, there will not be much temperature increase out of the injection pump. At 0.0005 volume/volume/degreeF you would need a 100F increase in fluid temp to equal the difference in density due each 1000 psi increase pressure.

Flow = Cd * Area * sqrt(dP * roh/2) for turbulent flow

Flow = volume/time

volume/time = Cd * Area * sqrt(dP * roh/2)

Density of Diesel Fuel is ~850 g/L and assuming an approximate 1/2% per 1000 psi compressibility and that it's linear (it generally is - this is bar napkin engineering here) that's a 913.75 g/L @ 15Ksi to 935 g/L @ 20Ksi or a ~2.3% increase in density. This gives you ~17% more volume in the same time period assuming that area and Cd stay constant (area is a good assumption, Cd - probably not, but lets say it is for discussion) with a corresponding 33% increase in input power to the injection pump (and accounting for efficiencies, more like 40-45%) due to the higher pressure.

So a 17% volume increase, 2.3% density increase and 40% input power to the injection pump for the above scenerio. I think the pressures are more like 4000 psi on the rotary pumps, but the idea is the same.

Any theories on why hot fuel is better?

 

[JLL]

work

If the fuel temp does not increase much from the pump then where does the heat go? raising the fuel pressure a couple thousand PSI is a lot of work. The fuel is HOT. This is the reason extra fuel is pumped through the pump and returned to the tank. The tank actuall gets warm on longer drives.

 

[rob61194]

warm is good but not too hot.

Iam a truck driver. With the newer electronic diesel engines they are returning so much hot fuel that fuel coolers are becoming popular. If the fuel gets too hot it can cause almost as much problems as fuel gelling in the winter, also if the fuel is too hot it will lower fuel mileage also.

 

[Fix_Until_Broke]

If the fuel temp does not increase much from the pump then where does the heat go? raising the fuel pressure a couple thousand PSI is a lot of work. The fuel is HOT. This is the reason extra fuel is pumped through the pump and returned to the tank. The tank actuall gets warm on longer drives.

Energy has various forms, potential, kenetic, thermal, pressure, chemical etc.
In the pump you are adding energy to the fluid (fuel) by increasing it's pressure, it now has more potential energy than it did before. When the pressurized fluid leaks out the clearances in the pump/injector, all of that potential energy that was added by the pump gets turned into heat due to friction in the fluid - there was no work done (applying a force over a distance for example). The temperature of the fuel does rise some due to the fact that it is compressible (same reason that the cylinder temp increases on the compression stroke - air is MUCH more compressible than fuel), but it's only a few degrees.

So in summary, we took fuel with a certian ammount of energy from the fuel tank, added energy to it in the injection pump in the form of pressure, used a percentage (most) of that energy added by the injection pump to accelerate the fuel through the nozzles in the injectors (trading pressure energy for kenetic energy here) atomizing it into a fine mist which self combusts (releasing it's chemical energy) due to the increased temeprature in the cylinder (the energy to raise the temperature in the cylinder came from an earlier combustion cycle either in expansion work from another cylinders combustion event or kenetic energy stored in the rotating assembly in the case of a single cylinder engine) which creates heat which causes the combustion gasses to expand and drive the piston down (finally doing some work by applying a force over a distance) which is translated into rotational work via the connecting rod and crank shaft which rotates with a given ammount of torque that is used to turn the driveline and accessories (such as the injection pump for example ). Whew...now, how fast all of this happens is power (work/time), and how long you do it is energy (power*time). Back to the energy added to the fuel in the injection pump...what didn't go into accelerating the fuel through the nozzles is leakage in the pump and injectors (and mechanical friction in the injection pump, which also ends up as "heat"). This fuel that leaked had energy added to it to bring it up to pressure, but it didn't do any work. This energy was converted into "heat" due to the friction in the fluid (viscosity) as it goes to a lower pressure through the clearances in the pump and injector. This is what makes the fuel in the fuel tank warm up. 1 degree F per ~140 psi, so a 3000 psi injection system should raise the temp by ~21.4F, a 30,000 psi injection system would raise the temperature by ~214F. The extra fuel circulated by the transfer pump in the injection pump is used to dilute this hot fuel with cooler fuel from the tank (which acts as a heat exchanger of sorts).

Sorry this got long - does this help?

 

[Fix_Until_Broke]

Talked to a fellow diesel enthusast about this - the only thing we could come up with was that on the maximum effort applications (sled pulling, drag racing, etc) where they are dumping in copious ammounts of fuel (ie: running a 12 cylinder injection pump on a 6 cylinder engine to get enough fuel in) that they need to put some extra heat in the fuel to get it to burn well. A lot of these engines are also running compression ratio's in the low teens and need a can of ether in each hand both spraying into the turbo just to get them to run on an 80 degree night.

Any theories as to why hotter fuel might be better?

 

[weasel]

I still think that it is thinner and atomizes easier and you get a better, more complete burn. Its almost like we need a fuel heater before the injector pump and move the fuel temp sensor somewhere else, like before the filter.

 

[Slave2school]

Why not have a modified thermostatic T made up and apply the KFC mod to counter the hot temps to your satisfaction (or what the ecu sees anyway).

 

[weasel]

Well I don't have the OEM filter anymore so a modified tee I won't need to do. I thought about the KFC mod, but I think it would be hard to calibrate it so that the ECU would see what the fuel temperature should be, not what it would be. I suppose you could take fuel temp readings when the car is cold, then readings again when things are warm and then you'd have a good idea of where to start. Relocating the temp sensor would be the ideal thing though ...

 

[JLL]

Hot Pump

Fixtuntillbroke, nice write up in responce to my questions. I actuall have a very good understanding of thermodynamics and diesel fuel injection. I agree with your statements but think you might be missing one point. The heat generated in the pump from friction and pumping losses are also absorbed by the fuel sent to the injectors. Yes, most heat is removed by the pass through fuel. The get a idea of the amount of heat in the fuel look up the horse power required to drive the pump minus the amount of work to compress the fuel minus the cooling through the body to ambient minus the temp increase and mass of the return fuel. Simple energy balance but the left over energy is in the form of heat in the injected fuel.
I actually worked with a very sucessful pulling truck, as a engineer, and we cooled our fuel, packed the pump with bags of ice some nights.