Vapor lock questions for the hotter climate guys

[5thhorsemann]

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.

[doradox]

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 July 30, 2011 by doradox

[cygnusx1]

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.

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 July 31, 2011 by cygnusx1

[Captain Obvious]

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, 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.

[doradox]

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, 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.

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

Steve

[Captain Obvious]

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?

[Captain Obvious]

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.

[doradox]

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

[cygnusx1]

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.

[doradox]

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

[Captain Obvious]

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. 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?

[5thhorsemann]

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.