Injector Extension?

[icanfixall]

If we know the cylinder offset we can time off any of the 8 cylinder hard lines using the clamp timing method known as pulse timing. As posted, the lines do ballon just enough to make a noise or move that the clamp can pick yp. Try running our engines without the hard line vibration clamps in place. The vibrations from the fuel pulsing thru the lines will crack the lines. Did that and paid big for it when I left off the clamps on the drivers side. Broke #2 line 15 miles from home. Ruff drive home after work at nite. I had no experiance on these engines way back in 97 so the dealer got the job. About $400.00 later job was done. The service writer told me they would have to remove ALL the lines to replace only one of them.... I got hosed Billy.. I got hosed big for that. After that hosing a dealer never saw my rig again in their bays. I learned a costly lesson that day.

 

[jim_22]

This is an interesting question! The pressure in the fuel line is pulsed (mechanically) and this pulse is used to regulate the injector to let fuel through. I had a neat tachometer once (called the "Tiny Tach") that consisted of a little sensor that clamped onto an injector line. The sensor picked up the fuel pulses in the line and was a perfect tach since every revolution of the engine makes exactly one pulse in each injector line. Notice the lines are not exactly the same length... but they are different in order to time the arrival of the fuel pulses, taking into account also the rotation of the pump.

 

[Agnem]

Try to think of it like a garden hose. We've all seen the hose swell when you turn on the water. If you throttle the spray handle on and off, you can watch the hose expand and contract. The whole hose does it at once. Not so much like a bubble. That's what the injection lines do. More length means more time to expand and contract. Its why our Moose Mister injectors help trucks run better. It decreases the "swell and dwell" as I like to call it. Because with stock BB injectors, the pump is done pumping before the injectors are done injecting and the line is done shrinking. The clamp on probes are actually measuring the capacitance of the injection line. In an electrical circuit, the gauge of a wire affects its capacitance. When the line expands, the metal becomes thinner, and that translates into less capacitance. This can be detected very accurately and very quickly by our timing meters.

 

[icanfixall]

Very well said Mel.

 

[laserjock]

Huh. I always thought it was a little load cell in the clamp litterally detecting the pulse. I guess I learned something.

 

[franklin2]

So the more modern injection systems that use a common high pressure pump and rail don't have this problem so much? So that means more accurate injection timing events?

 

[BR3]

so then theoretically if one were to make a line hard enough not to balloon, you could make lines whatever length you want it right? within reason of course....., I wonder what the effect on timing would be. I don't guess it matters really, just thinking out loud

 

[needlenose]

As I understand it, while liquid is considered non-compressible for all intents and purposes (for example, for braking), it still doesn't transmit pressure instantaneously enough for fuel injection purposes. Think of it like a shock wave...it may go very fast by "normal" standards, but with a diesel, pressure is being applied to each line once every other revolution...so, 28 times per second at 3400 RPM (3400 divided by 2, then divide that number by 60). To be honest, I've never tried installing a shorter or longer line myself so I can't say definitively that it's a bad idea, but if Stanadyne, Bosch, etc. felt it necessary to spend the time and money designing and mabufacturing each line at exactly the same length (even though that creates problems when dealing with lines close to the pump), I figure there has to be a reason for it

This is pretty much the same thing that Burman and DeLuca found in their research. It's about how fast the pressure wave makes it to the injector. Their book, published in 1962, can be found here:
http://babel.hathitrust.org/cgi/pt?id=mdp.39076006517911

From what I understand it is pretty much the bible for mechanical injection. I recently posted a response here indicating that, according to Pascal's principle, shortening a fuel line wouldn't affect timing. This is incorrect, but not for the reason that I was given here; which was fuel oil compressibility.

In chapter 5 "Injection Characteristics" Table 4, there is a list of factors which influence speed-delivery of fuel to the injector, or how fast the pressure wave reaches the injector(timing). They list fuel compressibility as "Slight" remarking that "Volume and pressure differential too small".

I haven't read the entire book, (there is more information there than any one human will ever want to know about mechanical injection), but my research seems to indicate that, regarding the fuel line itself, one of the greatest factors influencing the elasticity modulus within the fuel column is the material the line is made of. Changing out one fuel line with a stainless steel brake line of the *exact* same length will eventually trash the engine. This is because the metalurgical difference between the lines is great enough to effect the elasticity modulus which *will* have an impact on the speed delivery and timing.

So in reality, trimming the flare off a line to replace a stripped nut and reflaring would result in about .25" difference; probably immeasurable regarding timing. It would probably have the same effect as mixing a brand new stainless fuel line with 7 other 20+yo lines. They won't have the same age-induced properties and thus, the elasticity modulus will be effected. Again, probably an immeasurable amount.

At any rate, the book fascinating. They hit everything. How do you calculate the effect of rising cylinder pressure against the fuel column when the injector opens? It would take years to digest all the mathematics and theory in that book.

In the end, it's simpler to just leave the lines alone.

 

[jim_22]

This is pretty much the same thing that Burman and DeLuca found in their research. It's about how fast the pressure wave makes it to the injector. Their book, published in 1962, can be found here:
http://babel.hathitrust.org/cgi/pt?id=mdp.39076006517911

From what I understand it is pretty much the bible for mechanical injection. I recently posted a response here indicating that, according to Pascal's principle, shortening a fuel line wouldn't affect timing. This is incorrect, but not for the reason that I was given here; which was fuel oil compressibility.

In chapter 5 "Injection Characteristics" Table 4, there is a list of factors which influence speed-delivery of fuel to the injector, or how fast the pressure wave reaches the injector(timing). They list fuel compressibility as "Slight" remarking that "Volume and pressure differential too small".

I haven't read the entire book, (there is more information there than any one human will ever want to know about mechanical injection), but my research seems to indicate that, regarding the fuel line itself, one of the greatest factors influencing the compressibility modulus within the fuel column is the material the line is made of. Changing out one fuel line with a stainless steel brake line of the *exact* same length will eventually trash the engine. This is because the metalurgical difference between the lines is great enough to effect the compressibility modulus which *will* have an impact on the speed delivery and timing.

So in reality, trimming the flare off a line to replace a stripped nut and reflaring would result in about .25" difference; probably immeasurable regarding timing. It would probably have the same effect as mixing a brand new stainless fuel line with 7 other 20+yo lines. They won't have the same age-induced properties and thus, the compressibility modulus will be effected. Again, probably an immeasurable amount.

At any rate, the book fascinating. They hit everything. How do you calculate the effect of rising cylinder pressure against the fuel column when the injector opens? It would take years to digest all the mathematics and theory in that book.

In the end, it's simpler to just leave the lines alone.

Very cool reference. The propagating bulge exists indeed because the fluid is incompressible. There is a nice simple picture here:
http://en.wikipedia.org/wiki/Fluid–structure_interaction

 

[jim_22]

so then theoretically if one were to make a line hard enough not to balloon, you could make lines whatever length you want it right? within reason of course....., I wonder what the effect on timing would be. I don't guess it matters really, just thinking out loud

The line cannot not "balloon" because the liquid cannot be compressed. It is only a matter of how much. You want that balloon because it opens the injector nozzel.

 

[The Warden]

So the more modern injection systems that use a common high pressure pump and rail don't have this problem so much? So that means more accurate injection timing events?

As I've always understood it, that's correct, since on the more modern systems, the opening/firing time is controlled electronically directly at the injector, instead of being controlled mechanically by an injector pump. This is also why it's practical to have multiple, shorter injections for every power stroke for emissions, noise, and power purposes. That also makes for considerably more expensive "smart" injectors, compared to the "dumb" injectors (and "smart" injector pump) that our trucks have.

BTW, it's worth noting that the old 2-stroke Detroits have a primitive version of a common-rail injector setup...you have a fuel pump pressurizing a fuel line cast into the cylinder head, and an extra lobe on the camshaft drives a rocker arm that pushes the fuel injector to pop it open to fire the cylinder. Very simple (except for the fuel governor system), but this also means that a timing curve couldn't be built in, so you couldn't optimize the timing for a given RPM...I think that that's a big part of why the injector-pump driven systems superceded the older design, until electronics made a newer, higher-pressure common-rail system viable again...

 

[icanfixall]

Common rail fuel injection systems have a much higher injection pressure on the electronic injectors. The psd engines can inject fuel 6 times per cylinder when it fires. The common rail pressures must be at least 20,000 to open the injectors and it can reach as high as nearly 50,000 lbs. They are far different than our mechanical injection system. The electronic injectors are solenoid open and closed types. Our mechanical is pressure continues to increase till the spring set pressure is overcome. When our system is running we have the pop pressure on the hard lines all the time. Some of the electronic injectors have 5 ports in the tips where we have just one. I suspect if we could get 3 or 4 small holes in the tips and increase our injector pressure to say 2500 lbs we might have a killer engine. Making injector tips and running that high of a pressure will reduce the life of our injection pumps. Mel and I talked in depth about this years ago. This was when he was first designing the Moose Misters. Ever get a chance to look at a stage V1 injector you MIGHT be able to see the 5 square cut holes in the tips but probably not without a jewelers loupe. They are that small.... And very expensive.