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Vapor lock questions for the hotter climate guys

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I well know what superheated means. Water at standard pressure that is at 213 deg F and not boiling, is superheated. The reason I bring superheated into my theory is that once the pressure is dropped, or the vibration of the pintle is started, THAT alone could bring the fuel to change phase, from a superheated state, or even just skipping the superheated state. Yes, it could all happen without ever being superheated. There is also hysteresis between the phases. So maybe there is some instantaneous point in time when the fuel is superheated, maybe it just vaporizes without ever becoming superheated. I don't know for sure. Fastwoman is right in the cooking pasta observation. Microwaving pure water, which boils the instant you drop something into it, is another example of superheated water gone wild. Superheated states, are highly unstable, which would make a liquid in this state much more likely to vaporize by a seemingly insignificant catalyst.

Edited by cygnusx1

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Please forgive me for not knowing the intricate details of the Z's FI system, but...

You made mention earlier of the batch type injection concept where that all the injectors open at the same time for the same duration. Is that what the 280Z uses?

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So maybe there is some instantaneous point in time when the fuel is superheated, maybe it just vaporizes without ever becoming superheated. I don't know for sure.

Also, but not evidence, superheating, is relevant to this theory. In fact it's a critical point.

So is superheating critical to your theory or is it something that maybe sort of might be happening? Can cogently explain why superheating is a critical point?

Steve

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I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too. Superheating may or may not be critical to the theory. But I now think it is. I just figured that a single injection happens pretty quickly (2-5ms), so the if the fuel is phase changing, it's happening pretty quickly. A liquid in a superheated state would be the first, and fastest to flash. So if you have a column of liquid with a pressure gradient, "above boiling pressure" at one end, and "below boiling pressure" at the other end. Naturally, somewhere in that column there is a segment of critical pressure. There is also a place in that segment where a smaller segment of superheated liquid lives. That small segment may be the "seed" for the instant flash, so to speak. This is really getting microscopic, but it's all perfectly feasible and I think it happens. It happens when the conditions, and fuel quality, fit the mold.

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I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too. Superheating may or may not be critical to the theory. But I now think it is. I just figured that a single injection happens pretty quickly (2-5ms), so the if the fuel is phase changing, it's happening pretty quickly. A liquid in a superheated state would be the first, and fastest to flash. So if you have a column of liquid with a pressure gradient, "above boiling pressure" at one end, and "below boiling pressure" at the other end. Naturally, somewhere in that column there is a segment of critical pressure. There is also a place in that segment where a smaller segment of superheated liquid lives. That small segment may be the "seed" for the instant flash, so to speak. This is really getting microscopic, but it's all perfectly feasible and I think it happens. It happens when the conditions, and fuel quality, fit the mold.

Isn't it also possible that ALL the contents of the injector are already vapor before the injector opens? I think it would be more likely than your scenario where the exact conditions for the existence for some, however small, amount superheated liquid have to be present to cause the fuel to experience the phase change at exactly the moment required for it to cause a problem. So to my thinking, superheating isn't critical to explain vapor induced drivability problems in EFI cars.

I think your tortured hypothesis may be possible but not one that Occam's razor wouldn't slice the heck out of when speaking , in general, about drivability problems suspected to be caused by fuel, heat, and pressure not playing well together in an EFI system.

Steve

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Yup that is possible. But according to the manual, it's not. Then again, the earth was flat once.

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Thanks for digging up that tidbit, Dave! I think that MIGHT be another mystery solved. Now I won't fret so much when my hot engine re-starts roughly. Maybe the solution lies in a different design of injector. :)

BTW, I forget who mentioned Datsun's tidbit about goosing the throttle for a hot start, but I don't think that will help much. I've tried goosing the throttle AFTER starting, and the engine still runs roughly. It doesn't even out until I pull out of the driveway and head down the road.

Edited by FastWoman

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There is not much you can do to clear the vapor, other than drive it a bit after it starts. Sometimes it barely idles, so you can rev it, but the best thing is to place a moderate load on the engine which will open the injectors fairly "wide". Leaving the hood open is usually enough to prevent it in the first place. I wonder if any additives can raise the vapor pressure of the fuel, for experimentation.

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Yup that is possible. But according to the manual, it's not. Then again, the earth was flat once.

That, I think, stems from the definition of "vapor lock" which seems to have now evolved to mean any vapor related drivability problem. In the 70s maybe not so much.

Steve

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Wow, I broke a few ribs falling down a flight of steps Tuesday night and have been laid up for a few days. I assure you it is painful, but not as painful as this thread has become.

SUPERHEATING

The state of pretty much any matter depends on two things, temperature and pressure. Molten rock, for instance, in a liquid state can be subjected to enough pressure as to freeze back into a solid state, regardless of temperature. Likewise, under the proper circumstances, solid rock can be subjected to a sufficient bombardment of thermal energy as to cause it to go directly from a solid state to a vapor state, as demonstrated in volcanic eruptions. Superheating is a term which describes the amount of thermal energy that a given form of matter needs to absorb in order to change from a solid state directly to a vapor state, thereby skipping its liquid state altogether. Super heating has no place in a vapor locking discussion.

EFI

As for the FI discussion, when the injector opens, the orifice opens into a VACUUM, thereby radically altering the boiling point of the pressurized fuel, which would be aggravated by, fuel that is many degrees above the boiling point (at atmospheric pressure), along with the hot environment of the combustion chamber. This causes a lean condition (which at some point will become too lean to burn), detonation and other problems associated with the IC engine. The delta T of the specific fuel blend, the amount of mass the liquid fuel comes into contact with (once the pressure is removed from the fuel), the thermal coefficient and temperature of that mass being encountered by the fuel (the ability of the various metals to transfer heat) all play a roll in these conditions (there are many other factors which also have effects on combustion). The fact of the matter is, that as long as your fuel pump has access to liquid fuel and is able pressurize a closed system with that liquid fuel, any vapor will be sufficiently compressed as to return to its liquid state in short order. SO NO, AN EFI CAR CAN NOT SUFFER FROM VAPOR LOCK.

CARBURATION

Carbureted engines are completely different in so much as the fuel must exist in within the bowl, in a liquid state, at atmospheric pressure, in sufficient quantities, as to feed the jets with enough liquid fuel, that can be atomized again in sufficient quantities as to sustain combustion. The inability of the delivery system to supply an adequate amount of fuel to the carburetor bowl, is defined as VAPOR LOCK.

THE QUESTION IS (WAS)

What crafty little tricks have you desert dwellers come up with to minimize the vapor locking issues inherent to early Z’s?

Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem, so the car runs well in hot weather, the engine compartment stays as uncluttered as possible, and I don’t drain my bank account. I did enjoy the thread though.

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Wow, I broke a few ribs falling down a flight of steps Tuesday night and have been laid up for a few days. I assure you it is painful, but not as painful as this thread has become.

SUPERHEATING

The state of pretty much any matter depends on two things, temperature and pressure. Molten rock, for instance, in a liquid state can be subjected to enough pressure as to freeze back into a solid state, regardless of temperature. Likewise, under the proper circumstances, solid rock can be subjected to a sufficient bombardment of thermal energy as to cause it to go directly from a solid state to a vapor state, as demonstrated in volcanic eruptions. Superheating is a term which describes the amount of thermal energy that a given form of matter needs to absorb in order to change from a solid state directly to a vapor state, thereby skipping its liquid state altogether. Super heating has no place in a vapor locking discussion.

EFI

As for the FI discussion, when the injector opens, the orifice opens into a VACUUM, thereby radically altering the boiling point of the pressurized fuel, which would be aggravated by, fuel that is many degrees above the boiling point (at atmospheric pressure), along with the hot environment of the combustion chamber. This causes a lean condition (which at some point will become too lean to burn), detonation and other problems associated with the IC engine. The delta T of the specific fuel blend, the amount of mass the liquid fuel comes into contact with (once the pressure is removed from the fuel), the thermal coefficient and temperature of that mass being encountered by the fuel (the ability of the various metals to transfer heat) all play a roll in these conditions (there are many other factors which also have effects on combustion). The fact of the matter is, that as long as your fuel pump has access to liquid fuel and is able pressurize a closed system with that liquid fuel, any vapor will be sufficiently compressed as to return to its liquid state in short order. SO NO, AN EFI CAR CAN NOT SUFFER FROM VAPOR LOCK.

CARBURATION

Carbureted engines are completely different in so much as the fuel must exist in within the bowl, in a liquid state, at atmospheric pressure, in sufficient quantities, as to feed the jets with enough liquid fuel, that can be atomized again in sufficient quantities as to sustain combustion. The inability of the delivery system to supply an adequate amount of fuel to the carburetor bowl, is defined as VAPOR LOCK.

THE QUESTION IS (WAS)

What crafty little tricks have you desert dwellers come up with to minimize the vapor locking issues inherent to early Z’s?

Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem, so the car runs well in hot weather, the engine compartment stays as uncluttered as possible, and I don’t drain my bank account. I did enjoy the thread though.

Superheating. Not commonly defined as you have but I agree that it's not relevent.

http://www.answers.com/topic/superheating

http://www.wordiq.com/definition/Superheating

http://en.wiktionary.org/wiki/superheating

Any vapor "can" be compressed enough so it won't turn to vapor at any temperature. But the fuel pump in an EFI system is regulated to a max pressure therefore if the fuel temp is high enough it most certainly can vaporize. Whether or not this is called vapor lock is another thing altogether. I'm with you on the definition though as vapor lock has been around since the dawn of carbureted IC engines.

Pop your hood when you park for short periods on hot days. Cheap.

Move the fuel filter to the pressure side of the pump. A restricted filter lowers the pressure on the inlet side of the pump.

Marginal if any benefit.

Get an electric pump and mount it low in the engine compartment or move it completely out. The high mounted manual pump means lower fuel pressure on the inlet side of the pump and exposure to some of the hottest air in the engine compartment.

Electric radiator fans with a thermostatic or timed cut off and wired to run with the ignition off will create air flow and help reduce heat soak. Make sure your battery is up to the task though.

Steve

Edited by doradox

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Ouch sorry to hear about the ribs. That's one of the most painful things, and I can't image our discussion has been that painful. Sorry you had to read it all.

I am not sure where you get your definition of superheating. It seems like you are talking about sublimation, perhaps? Whatever, really. I think we have figured out that an EFI system can get vapor in it, but it's not as critical as with a carbureted system because it should never effect the pumping of the fuel.

Depending on what problem the vapor causes, it may be called vapor lock, or not. Maybe we can just say, "my Z has the vapors", when it's not causing pumping issues. LOL

Question though. Isn't vapor lock really just pump cavitation anyhow?

Tricks? A long time ago, I added 1/8" thick teflon washers between the fuel rail mount tabs and the intake manifold. I also had wrapped the fuel lines with a glass backed foil at one point. By far the best result has come from leaving the hood popped at least 10".

Edited by cygnusx1

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Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem. I did enjoy the thread though.

I'm guilty as charged, and I apologize. I would like to be the first to admit that I've offered nothing to help with your original question. I found the topic interesting and got sucked in with the intent of defending the laws of physics. And just when I thought I would be able to resist, :tapemouth: something like this happens...

Any vapor "can" be compressed enough so it won't turn to vapor at any temperature.

Uhhh... No.

There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)

I'm really trying to give up the physics. Really!! As a matter of fact, thermo was my worst class ever. I absolutely hated it.:D

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I'm guilty as charged, and I apologize. I would like to be the first to admit that I've offered nothing to help with your original question. I found the topic interesting and got sucked in with the intent of defending the laws of physics. And just when I thought I would be able to resist, :tapemouth: something like this happens...

Uhhh... No.

There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)

I'm really trying to give up the physics. Really!! As a matter of fact, thermo was my worst class ever. I absolutely hated it.:D

Yeah, your right, it was a little hyperbole more than anything.

Steve

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I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too.

So is the damper intended to reduce changes in pressure in the positive, or negative direction, or both? In other words, suppose your fuel rail is supposed to be at 30 psi... Is the damper supposed to provide some temporary volume to swamp out pulses above 30 psi, or supply a transient supply of fuel in the event that the fuel pressure drops below 30 psi? Or both?

I've never thought about it that intently before. You got any idea?

I mean, who knows what's happening at speed. You got the injectors are opening and closing. They open and fuel goes out, so physics dictates that the pressure must drop. And then they snap shut, probably momentum hammering the fuel rail and sending a very high spike back through the line. And then you have the fact that the pump output is probably not be a perfectly steady pressure either.

So what's your take on the damper?

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Yeah, your right, it was a little hyperbole more than anything.

The really unfortunate thing for me is that the main reason I hated thermo so much was that I (at the time) saw absolutely no practical application for it in my future. I barely squeaked through!! Little did I know...

If I had known then how much of it was easily applicable to automotive applications, I would have paid attention. There is so much more that I could have gotten out of it if I simply would have given a crap.:stupid: The stupid things you do that don't seem stupid until later.

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The really unfortunate thing for me is that the main reason I hated thermo so much was that I (at the time) saw absolutely no practical application for it in my future. I barely squeaked through!! Little did I know...

If I had known then how much of it was easily applicable to automotive applications, I would have paid attention. There is so much more that I could have gotten out of it if I simply would have given a crap.:stupid: The stupid things you do that don't seem stupid until later.

I entered engineering after 20 years of wrenching as an ASE Master tech and really loved learning the math and physics behind all the things I had learned from experience. It made even thermodynamics kinda fun.

Steve

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Common we can get this thread to 100 posts!

I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.

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Common we can get this thread to 100 posts!

I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.

Would you say the damper is for the benefit of NVH or?

Steve

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I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.

So there's nothing up in the engine compartment to mitigate high frequency pulses? You've got the FPR up there for low freq stuff, but nothing for high frequency effects like the injectors opening and closing?

I'm wondering if there was a device close to the injectors capable of dealing with high frequency effects and regulating the fuel pressure better than the FPR, it might help with the very hot restart issues we were discussing. The thinking being that it might do a better job of regulating the pressure locally and preventing any vapor from forming in the system, even if that vapor is a recurring transient.

I entered engineering after 20 years of wrenching as an ASE Master tech and really loved learning the math and physics behind all the things I had learned from experience. It made even thermodynamics kinda fun.

Yeah, I went the other way. :geek: Engineering first. I would have gotten more out of it if I'd done it the way you did. Heck... Maybe even fluid dynamics and strengths of materials would have been ummm.... dare I say tolerable?

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Do you really think a high frequency damper would do anything to improve fuel delivery at RPMS over 1000 to 1500? On a 6 cyl your lines see 3000 PPM or 50 pps at 1000 RPM. The gasoline is light enough alone, adding the ethanol makes it even lighter, I wonder where the pressure pulse would flatline, RPM wise. If you look at how a hydraulic system behaves (using hyd. fluid, or brake fluid, which are heavy and dense compared to gasoline) at low (pump) rpms the systems are slugish and you can feel the vibrations through the controlls, like peddal feedback on brakes. But if you rev the whole thing up it gets smooth as silk. I would think the gasoline would act as its own shock absorber at a very low rpm. Anyone running a mechanical fuel pressure gauge that can speak to that?

Back to the VL. I'm using pheonalic washers on my fuel line at the head, same stuff the carb heat isolators are made of. The hard lines are wrapped in fiberglass and have a 3 mil. reflective aluminum shield tape (one layer thick) over the FG. The fuel filter is before the pump, and mounted at about the same height, thats how I came to the VL conclusion so quickly. I could see that the filter was empty, and when it did begin to fill the fuel was boiling within the filter itself. I think the pusher pump is going to be my savior on this one, and I also think I am just going to stick the Faucet pump back at the tank because the existing mounts and wiring will fit rite up, after all, it's cheep enough and they are very dependable from what I've heard and read.

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Uhhh... No.

There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)

I was thinking about this and something didn't seem quite right. If a liquid held at a constant volume is heated past the critical point how would the "gas" that now exists be any different than the liquid. Apparently it isn't.

http://en.wikipedia.org/wiki/Phase_%28matter%29

"At the critical point, the liquid and gas become indistinguishable. Above the critical point, there are no longer separate liquid and gas phases: there is only a generic fluid phase referred to as a supercritical fluid. "

So a gas can be compressed to at least a state which is not a gas anymore.

Steve

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I was thinking about this and something didn't seem quite right. If a liquid held at a constant volume is heated past the critical point how would the "gas" that now exists be any different than the liquid.

So a gas can be compressed to at least a state which is not a gas anymore.

Haha! Did you look at the list of references for that page and the ones similar? It looks like someone is bucking for a good thesis grade. A lot of the references cited are less than five years old and lots of them are clearly research!

This is my favorite... Number 25:

Ye, Xiang-Rong; Lin, YH and Wai, CM (2003). "Supercritical fluid fabrication of metal nanowires and nanorods templated by multiwalled carbon nanotubes". Advanced Materials 15 (4): 316–319. doi:10.1002/adma.200390077.

Now there's a citation I can trust!

As a matter of fact, I was just messing with some metal nanowires and nanorods templated by multiwalled carbon nanotubes yesterday in the shop.

Seriously though, good catch. :beer: Research continues and concepts are refined. Haha! Back when I was in school, we got by just fine with only three phases. Seems they weren't teaching this at your school either, huh?

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Do you really think a high frequency damper would do anything to improve fuel delivery at RPMS over 1000 to 1500? On a 6 cyl your lines see 3000 PPM or 50 pps at 1000 RPM.

It really doesn't matter, but I don't get your math...

I do this:

Assuming batch fired injectors on a four stroke engine...

At 1000 rev/min there are 500 injections/min

500 injections/min = 8.3 injections/sec

Do I think a high frequency damper might be able to do something to quiet 8.3 pulses per second?

Yes.

Back to the VL.

On your VL issues, it sounds to me (the non-expert on such matters) that you're doing everything right except for the removal of the pusher pump.

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