MPG fooler - Design phase

[ISX]

liquid fuel is not compressible therefor it cannot accumulate heat energy by being compressed. Gasses are compressible and therefor can accumulate the heat energy from the larger volume being compressed into a smaller volume. Just as you are putting more air in a smaller space raising the pressure you are putting the latent heat from the larger volume into that smaller space raising the temp. You point this out

"But on an engine, just 17:1 raises the temp from 0F to

967F (if there were no losses). Obviously compressing air and fuel are 2 different things".

Fuel has a flash point and an auto ignition temp. For diesel fuel in general the flash point is 62*C and the auto ignition temp is 210*C. Both are well under the 967F you calculate as a cyl temp rise from compression.

However the autoignition temperatures do change somewhat with the grade of diesel #1 is 177*C-329*C #2 is 254*C-2 and #4 is 263*C.

Source:

http://hypertextbook.com/facts/2005/EileenTang.shtml

http://en.wikipedia.org/wiki/Autoignition_temperature

http://en.wikipedia.org/wiki/Flash_point

So I believe what happens when an injector fires is:

1. The cyl compression raises the temp to above the flash point and auto ignition point of the fuel.

2. The injector fires spraying the fuel into fine droplets or mist in the cyl where the fuel absorbs heat to raise it's temp above the flash point at which time some of it becomes a gas.

3. The gas now being above the auto ignition temp begins to burn, further raising the cyl temp and flashing off and burning the remainder of the fuel being injected.

4. The injector continues to pop (chatter) injecting more fuel into the burning mass in the cyl until the injection cycle is terminated by the injection pump.

If the temp of the diesel fuel significantly raised by putting 4000 lbs of hydraulic pressure on it, it would flash inside the injector and high pressure lines and become a gas there, which would not be fun to be around. The other thing that makes me think this is the common rail injection system has fuel at a much higher pressure than 4000 lbs something on the order of 25,000 lbs I believe i have read. As far as I know there is no heat problem generated on the CR trucks by having the fuel at such high pressure.

I'm not an expert and I could be completely out in left field in my thinking, but this is what I have deducted from things I have read.

My point in thinking If the fuel were warmer going into the injection pump is it would be less viscous and atomize through the injector nozzle a little better perhaps speeding up the ignition a little. Whether or not it makes any difference in the injection and burn remains to be proven.

Jim

[SASQCH]

"As for the fuel blowing up inside the injector, I wonder if that would happen since there is no oxygen in there, kinda like water wont boil if there is a lot of pressure."

Sorry, I didn't mean to imply that the fuel would ignite inside the injectors and HP lines. Obviously it won't because as you point out there is no O2. I was thinking more that it would flash into a gas and raise the pressure in the lines to beyond their burst point. When water flashes into steam it expands 10,000 times in volume. I don't know how much diesel fuel expands when it flashes into a gas. I do know that when water boils and flashes into steam it absorbs a tremendous amount of latent heat and that's why the whole volume of water don't turn into steam instantly when it reaches 212*F at 14.7 lbs absolute pressure (sea level). The heat source has to supply the heat the gas absorbs when it flashes. So the greater the heat source the faster the water boils and flashes into steam.

You are correct that water will boil at lower or higher temps depending on the pressure on it and when it does it contains more or less energy depending on the pressure and temp. The high pressure steam driven ships the NAVY used before nuclear systems, used superheated steam from a pressure vessel (boiler) at temps and pressures exceeding 1200psi and as high as 1000*F, because the steam contained more energy and could drive the steam turbines much harder.

Just tidbits from my past.

Jim

[ISX]

"As for the fuel blowing up inside the injector, I wonder if that would happen since there is no oxygen in there, kinda like water wont boil if there is a lot of pressure."

Sorry, I didn't mean to imply that the fuel would ignite inside the injectors and HP lines. Obviously it won't because as you point out there is no O2. I was thinking more that it would flash into a gas and raise the pressure in the lines to beyond their burst point. When water flashes into steam it expands 10,000 times in volume. I don't know how much diesel fuel expands when it flashes into a gas. I do know that when water boils and flashes into steam it absorbs a tremendous amount of latent heat and that's why the whole volume of water don't turn into steam instantly when it reaches 212*F at 14.7 lbs absolute pressure (sea level). The heat source has to supply the heat the gas absorbs when it flashes. So the greater the heat source the faster the water boils and flashes into steam.

You are correct that water will boil at lower or higher temps depending on the pressure on it and when it does it contains more or less energy depending on the pressure and temp. The high pressure steam driven ships the NAVY used before nuclear systems, used superheated steam from a pressure vessel (boiler) at temps and pressures exceeding 1200psi and as high as 1000*F, because the steam contained more energy and could drive the steam turbines much harder.

Just tidbits from my past.

Jim

[SASQCH]

Ah, very interesting.

Expanding on this:

I was reading yesterday about how cold liquids have their molecules clump up and move around, whereas hotter fluids have their molecules moving around individually. That was water but maybe fuel is the same, and if it were the same then it stands to reason that hot fuel would atomize better since there are no "clumped" molecules.

So in theory we should be getting the fuel as hot as possible without having it blow up.

I don't think the fuel temp should be raised above the flash point of 62ºC (62 ºC = 143.6 ºF). If it goes above the flash point some of the fuel may flash into a gas and interfere with the injectors working properly.

Hmm, I have an idea since it is cold here. If I used a heat gun on the injectors for a while before the morning start, it would theoretically start better. I think that a heat gun isn't going to do much against that 1,000 lb heat absorbing chunk of iron called the cummins engine.

I would aim it away from the block but at the injectors and that should transfer all the heat through the fuel. Would be a neat test to do anyways.

[ISX]

That's what is holding me back from just slapping together a simple heat exchanger using engine coolant. I need some kind of adjustable temp controlled valve to regulate the coolant flow to keep the temp of the fuel below 140*F automatically once it is set. Jim

[SASQCH]

Yeah I was wondering how much of the heat would just go straight into the block. I think if I got it hot enough I could start it before all of the heat transfered.

John's 24V had a fuel temp on the edge module and if you drove it and let it sit for a long time, the temps would get to 150-160F. I wonder if being contained inside the fuel system like that would keep all of it from turning into a gas. Yes, I think so only some of the fuel would flash to gas thereby raising the pressure and raising the flash point. Just like boiling water in a closed high pressure vessel. As it flashes into steam the pressure goes up preventing more to water to flash until more heat is added to reach the new flash temp of the pressurized fluid. Interestingly if you remove the heat source from the boiler and allow it to cool back to it's starting temp the pressure also drops due to the steam condensing back into a fluid. I suspect that diesel fuel follows the same thermodynamic laws.

His fuel also didn't get hot too quickly while driving, might have got to 30 over ambient, which in the winter would mean it stayed cold, though I would like to hear from someone who has watched it in the winter. You would think the VP44 would then be more efficient since it is full of fuel, hence heating it up more. The only fuel mine sees is what it puts in the plungers.

Another thing to think about is the density of fuel changes with temp. You might have to step on it more with hot fuel than cold fuel, unless it is more efficient with the hot fuel. Yes, I think you are right here, I don't know how much the volume changes. But I do know it changes, go to a fuel station early morning after a cool night and fill your tank to the brim and wait for it to warm up with the day temps. You will have fuel running out by 5 or 6 PM.

So many factors

[steiner43511]

Once you get your fuel gauge - sell the EZ and get a COMP/JUICE/ADRENALINE more timing and power ......... 2-3+mpg generally

[Mopar1973Man]

Yes, I think you are right here, I don't know how much the volume changes. But I do know it changes, go to a fuel station early morning after a cool night and fill your tank to the brim and wait for it to warm up with the day temps. You will have fuel running out by 5 or 6 PM.

[SASQCH]

Yes that one is true I got called on a fire run for a HAZMAT spill. What had happen is exactly that the owner had filled his fuel tank totally rim top full and parked the truck on the street and it went from 55*F in the morning to over 115*F in the afternoon and the diesel fuel was perkin' right out of the fuel cap.

Needless the say the owner got slapped with a heavy fine...

[Mopar1973Man]

Oh if I want to see IAT over 130*F all I got to do is find a grade drop the exhaust brake and bam! IAT temp rocket up and stay up till I turn off the exhaust brake. But as for the rise at low boost I see the same thing but rolling into the boost pressure I typically see a fall in temps about 5-10*F typically. I think because at low velocity the air has time to pre-heat in the manifold since there is a coolant passage the runs along the bottom. But under boost your pushing air through so fast its not pre-heating as much... (My thought on it )

[ISX]

The IAT is slow to react. I noticed it when I took it out and was testing resistance values of it in water and stuff. You would put it in ice water, and it wouldn't do anything for a couple seconds then slowly start to figure out it was cold. I got more info from the physics wizards and indeed the boost and atmospheric pressure have NO effect on the temp rise you get when the piston compresses. Compression ratio and IAT are the only determining factors. Now more boost usually comes with more heat from compression in the turbo itself, so the IAT would be warmer due to that which would in turn create more heat during compression. But if the IAT was always the same, it doesn't matter what boost or atmospheric pressure is, the temp rise from the piston compressing will always reach the same point. So more compression means more heat, and higher IAT means more heat, that's it. More pressure in there from more boost means more volume and air molecules in there to burn, so the volumetric efficiency shoots up. Obviously colder air increases this efficiency further.

[Mopar1973Man]

After reading your post ISX it seem to be that if I can find the high point for MPG and just use a fixed IAT resistor that's all it matter then right? So as long as the ECM thinks in a nice warm summer day I should be good all the time right? (Trying to understand your math)

[dracozny]

Yup, I think self serve fuel stations should have signs warning of this hazard and telling people not to over fill their vehicles. ........... Jim

[ISX]

After reading your post ISX it seem to be that if I can find the high point for MPG and just use a fixed IAT resistor that's all it matter then right? So as long as the ECM thinks in a nice warm summer day I should be good all the time right? (Trying to understand your math)

[flagmanruss]

With fuel prices around here high... I don't ordinarily worry about topping up. I plead guilty however to topping right up the spout... fortunately my tank & fill are tight with no seepage... before hooking up to head out on trip. It's far enough home that I'm down close to a gallon, just getting there. I have been paying attention to the previous posts on this topic & have not topped up since... If/when I get a Draw-Straw I'd be concerned about seepage from the gromets. It would hurt to waste fuel at these prices, even if no one caught us. Russ

even in a non self serve state, the attendants automatically top off, around here anyways.

[Mopar1973Man]

Mine leaks at the grommet... But since I drilled the wrong size hole from what I found out that explains part of it. I was a unlucky person missing part of the manual explaining that part, no extra spring, no warranty card, no sticker, etc... But I'm happy with my AirDog 150 still going strong...

[Rogan]

Yup, I think self serve fuel stations should have signs warning of this hazard and

telling people not to over fill their vehicles.

Jim

[JOHNFAK]

Around here, they DO say "do not top off fuel tank" on the pumps.. On another note, I was able to get a little info on the piston differences between the 12v and 24v, and related to compression changes. The 12V has a 60cc bowl, and the 24v has a 64cc bowl, thus a touch less compression ratio. And while picking up my exhaust yesterday morning, he got a 12v and 24v piston out, so I could take a pic and show the physical differences of the bowls.. On the left, is the 24v with it's centered 64cc bowl. The right one is the 12v's offset 60cc bowl (since the injector is off to one side, rather in the middle.)

[SASQCH]

What are the 24V HO pistons like, are they the same as the SO pistons?

[stodg73]

Also, the pistons for the H.O. are different shapes than the S.O. due to the different injection pattern.