Fuel Injectors Rating

[buddy]

the injectors set injection pressure in it's entirety, no if's, and's, or but's about it

- the system will have 1850psi press if the injector springs are calibrated to 1850psi

- the system will have 2275psi press if the injector springs are calibrated to 2275psi

- the system will have 2700psi press if the injector springs are calibrated to 2700psi

So I asked the Stanadyne Engineering department about this, because this pop pressure is the line pressure goes against my understandings. The man said the line pressure will vary based on fuel volume flow. So at idle it may only just have a line pressure just above injector pop pressure, but at higher volume demand it will increase the pressure to the higher limits of the pump.

How do you increase flow out of a fixed orifice in a shorter period of time (higher RPM)? You increase the pressure.

Perhaps he didnt know what he was talking about either, but I wouldnt want to have people thinking marine injectors or 2700psi pop pressure will kill their IPs if it isnt that big of deal.

I couldnt get any documentation from them, everything is "proprietary".

One thing I would really like to know about marine injectors, is if the flow rating actually increases. Is the nozzle larger? Is there a flow rating for the stock injectors lb/hr or CC/min type, and is there any different rating with the high ouput injectors.

The pump may only put in so much volume per injection event, but with what I have read some amount left over gets recycled in the pump, and perhaps you could just have less recycled fuel if you get a larger nozzle.

Any injector builders out there?

 

[gmctd]

Good questions, Buddy - what he said is basically true - but, he did not imply that if you set 1850psi at low-volume idle, you would get 2750psi at 5000rpm - with 2750psi injectors, you also get 2750 psi at idle - that higher pressure across the low to high rpm band will destroy the rollers\camring, and is why S and GM settled for 1850psi as being sufficient for good injection spray pattern while meeting pump and injector longevity and warranty requirements

Remember: Diesel fuel is the sole lubricant and coolant in these IP's - other similar pumping plunger types use engine oil at engine oil pressure to lube the cam and followers - the low-viscosity low-lube fuel is merely pumped

At idle, the crank and IP shaft are turning relatively slowly, the rollers are riding up the ramps slowly, so the pumped pressure increases slowly - the injectors will pop at ~1850psi - idle flowrate is ~10.5mm3

At 5000rpm, the IP shaft is turning rapidly, the rollers are riding up the ramps quickly, pumped pressure is comparatively immediate, the injectors pop much more quickly, injection timing is advanced slightly - 5000rpm fwot fuelrate is ~66mm3

Remembering the constant-beginning variable-ending, fill-pump-spill concept, as you can see, the "spilled" excess fuel volume is way more at low rpm than at high rpm - same difference at low-rpm no load and low rpm, high load - the max flowrate outta this IP is somewhere between 75~90mm3, so there's even more excess that would need to be spilled, depending on the tuning - PCM controls all excess spill according to the load - flowrate limits, within design parameters of the camring\plunger dia, are set by the tuning

(And that's the difference in Diesel engines and those other engines: we can dump in 66mm at 1000rpm and the BTU's\power increase drastically because the fuel does not come in with the throttle-plate\lowrpm limited air intake charge- try that with those other engines, and they just flood out, big smoke no power)

"Hi-pop" injectors are recalibrated for higher pressure and retard timing slightly - marine injectors may get higher pop, but also get larger nozzles, which advance timing slightly

The limiting factor is PCM tuning - marine injectors won't give any more flowrate than 66mm with factory tune - they just dump it slightly quicker - they will give 75mm flowrate with 75mm performance tune, or 95 with 95 - the difference is the duration: they do advance timing slightly because flow-thru rate is less restricted than the oem stock injectors - they are also used more for constant-throttle service, where the Cap'n loads up the bevy of beauties in N'Awlins, points the 'cruiser towards Miami, setting the throttles for max (or min, depending on what the beauties promised him) cruising speed across the Gulf - the load never varies, so the throttles are never varied till the craft approaches the marina - usually also with those injectors comes a marine tune with different advance and fuel curves than for street vehicles, with their constantly varying loading and throttle input.

Marine injectors are calibrated to be used with higher output than stock output pumps

 

[gmctd]

Also remember that all pumps are designed with specific flowrate and pressure limits - fe, the oem lift pump is designed to pump 4.5psi at 15gph - that means it will pump 4.5psi at 1gph, or 10gph, or 15gph - it will pump 1psi at 17gph, and 0psi at 20gph - doesn't mean it's bad, just that spec'ed ratings have been exceeded

Somewhere in a pumping system is a regulator that sets max system pressure, and may also, due to design, limit system flowrate

In the DS4 6.5 case, there are 8 regulated pressure systems, one for each cylinder, each regulated by the injector for that cylinder - if 7 injectors are calibrated for 1850psi and one is calibrated for 2250psi, the other 7 cylinder pressures do not jump up to 2250psi, nor does the higher pressure fall to the lower pressure of the other cylinders

If 7 are oem injectors and one is a hi-flow marine injector, the other 7 do not become hi-flow systems, nor will the marine become a low-flow version

The injector is the system regulator for it's cylinder, independent (within specs) of the others

In the above cases, engine may tend to run ruff, and PCM may stentoriously object by setting a Cylinder Imbalance DTC at idle

 

[THEFERMANATOR]

I remember one of the pump gurus posting on this before, and basically pressure does go up with RPM's due to the weight of the fuel you are pushing through the lines and through the small orifice. The pop pressure is there to maintain a minumum pressure in the lines, but flow and resistance will dictate actuall pressure in the HP lines at the pump. You can see as high as 13.200(11,800 is the max sustaineable he said) I believe he said at the rotor head where the plunger is compressing the diesel out through into the line, but you won't neccesarily get that at the injector. I also remember it being posted that a DS-4 pump will almost certainly seize the rotor head or shear the drive off at 13,600 PSI, and this is why he warned against running marine high pops with a DS pump. Even though it is only a small increase at the the injector for pop pressure, by the time you couple that with the weight of the diesel and resistance through the line that extra 500 PSI can push you over the 13,600 thresh hold. I cannot verify this for certain, just what I remember discussing with him.

 

[gmctd]

I agree with your opening statement - always takes more pressure to overcome valve-spring pressure than to keep the valve open - as far as the rest, and other than identical injection timing, that's a more plausible reason for the hi-pressure thick-walled injector pipes in an 1800psi system - I remember using nylon tubing in 1800psi hydraulic systems, and thick-walled steel tubing like that for over 10000psi systems

The diameter and number of plungers and horsepower on the driveshaft are way enuff to produce those numbers - if you can get it verified, I'll modify some of my text to suit - fyi, I was never able to get anyone to offer information like that, not even via PM

I always hoped that if my input was wrong, someone in the know would have a conniption fit and post correct data just to prove me wrong - prollem being, that didn't happen, and it didn't take much to prove the retorters were almost always wronger than I was supposed to be

 

[Matt Bachand]

So the added fuel passing through the marine IP helps to cool it, and we are to assume S beefed up the marine pumps to handle the additional fuel flow and pressure.

Whats the reason we can't bolt a marine IP up to our 6.5's?

 

[buddy]

This is to get some thought process rolling and what my thoughts of how this injection works, and looking for some feedback.

So I had regular injectors, and now I have marine injectors. The PCM requests the same amount of fuel, about 8mm3.

If the marine or custom injectors have larger nozzles I would expect them to actually dump a little more fuel than a stock injector for the same PCM requested fuel rate.

This is how I think it works. The PCM requests a fuel rate, that is just what it wants, and it receives some feedback on the actual from the PMD, telling it the pulse width, but otherwise the PCM doesnt really know how much fuel went through. As long as the pulse width and timing was within tolerance the PCM doesnt bother you.

So if in that pulse width, if the nozzle is larger, allowing higher flow then more fuel would get squirted compared to a smaller nozzle, and the PCM would be none the wiser. And the real impact to the DS4 would be that less fuel gets recycled for the next injection event.

It may not work exactly that way, but that is my way of posing this and if anyone know for a fact it won't work that way.

Now the pop pressure changes the timing slightly, as gmctd said, increasing pressue delays injection slightly. So the nozzle would have to be larger to get the same amount of fuel out in the same time as an injector that popped earlier. This is because I believe the DS4 to work off of timing to a large extent, and higher pressure off of higher RPM of the crank.

So because the RPMs of your crank are still the same (regardless of the injectors used), I dont understand that the injection pressure would shift up because of higher injector pop pressures, just delay the start, and peak remains the same, based on the RPMs you are at (because faster spinning shaft is how it can inject faster/more flow??).

So does a higher pop pressure lead you to a higher max injection pressure, I wouldnt think so, because where does the pressure come from? And with a larger nozzle, if it has one then pressure would drop a little I would expect.

 

[ak diesel driver]

So the added fuel passing through the marine IP helps to cool it, and we are to assume S beefed up the marine pumps to handle the additional fuel flow and pressure.

Whats the reason we can't bolt a marine IP up to our 6.5's?

We can. $1400 and mechanical only. At least thats what I've read.

 

[buddy]

And with what I have observed from the PMD, I would like to understand more what it "drives" on the fuel solenoid.

To increase fuel it increases the amplitude of the signal it sends, higher voltage. And it can increase the period, longer time, pulse width. In park I have observed that the pulse width remains the same, but voltage increases with the fuel pedal and RPMs (1.5-6VAC). Does the voltage drive the fuel solenoid to open a specific amount, higher voltage opens the solenoid more so more fuel can flow into the chamber. That is what I have been thinking anyway.

I havent had the opportunity to tear one apart though, and cannot find any documentation on how they work. Again, "proprietary", which I hate that.

 

[buddy]

I also asked about what the pop pressures are recommended by Stanadyne, and he said the stock injectors for turbo'd 6.5s should pop around 2100psi, and that Marines were about the same. But the N/A 6.5s had lower pop pressure of 1850psi

 

[gmctd]

DS4 is constant-beginning variable ending injection system - FS valve open allows fuel from the plungers to spill back into the housing accumulator - valve closure intiates pumping event, valve reopening ends injection event

Marine hi-flow injectors were calibrated for a mechanical DB2 IP which had the fuel rate turned up, allowing more fuel flow thruput

A: the FS functions on current, not voltage - that's why you can use a 6" FS harness or a 72" harness without any degradation of function - if it were voltage-driven the 72" harness would be a dud and we'd all be eating PMD's off of intake-mounted heatsinks - injection is by valve closure - closure duration is variable, gated orifice size is not

B: the FS drives a small valve-plate, moving only 0.005" - that dimension is critical, which is why it is near-impossible to R&R a worn or failed FS in the field - the adjustment is done on the flow-bench - the valve is always open until commanded to close - fuel flows when the valve is closed - fuel is allowed to spill when open

So why is the FS so physically huge, to move such a small plate such a minute distance? Takes a lot of force on a large mass to control ^1800psi, takes a lot of current to get the valve moving within the time allotted at hi-rpm - rpm/60 = rps x #cyl/rotation = # injection events/sec = min # valve operations/sec

PCM operates FS based on viscosity of Diesel fuel at measured temperature, via the Fuel Temp sensor in the Optic Sensor - Closure Time in ms informs PCM of duration between power applied to FS and FS valve fully seated, which is affected by fuel viscosity and pressure - at that point, fuel pressure begins increasing, climbing toward injection pressure - PCM holds the FS closed for a matrix-calculated duration, Injection Pulse Width, which should allow the pressure to build and the indicated volume to flow after the injector pops

tbc.........

 

[bison]

lots of hi tech info,it fries my simple mind.

on the pop pressure,
there is plenty of rotary IP,s pumping fuel to injectors set at up to 3800 psi pop,on tractors and industrial engines. CAV is one of them,wich i believe is now stanadine as well.And these are aluminum pumps as well.
I cannot see why the DS4 could't handle higher pop pressure, I got my 95 inj set at 2200 when i rebuild them 40.000 km ago,and the IP has in excess of 200.000 km on it. It runs as strong as ever.

Injection duration is IMO more critical at idle than at 2000 rpm and up.

I was told by Pensicola,the Marine inj flow more fuel cause the return orifice is smaller than stock.
dont know what to believe.

What i do know is upping the press on stock injectors makes for a crispy running engine.I did this on three diff 6.5's and all show improvement,regardless of milage.

 

[Rhinopkc]

How about not raising pop pressure, but installing the high flow nozzles? Would that flow even more? Your injection event would start sooner and be flowing through the bigger nozzle.

 

[schiker]

I suspect lower pop pressure and big orifice would be poor initial spray pattern. I believe the affect would be poor idle low rpm/low fuel rates smoothness issues with less impact at higher rpm and higher fuel rates.

The pop pressure determines the minimum flow rate that starts the injection or more really where the rollers are at on the cam and kind of takes all the "slack" out of the injection event (for the nozzle size). The flowrate and nozzle together make up for a good spray pattern (atomization) and thus good clean crisp combustion.

 

[buddy]

The IP only receives the one PMD signal for injecting fuel, so how does it vary fuel flow at a constant pulse width if the FS is only open or closed?

 

[OregonHorseTug]

The IP only receives the one PMD signal for injecting fuel, so how does it vary fuel flow at a constant pulse width if the FS is only open or closed?

The pulse width IS the variable. Pulse duration determines fuel rate.

 

[buddy]

The pulse width IS the variable. Pulse duration determines fuel rate.

That cannot be the only determination, because it is not always variable, the width will stay the same with change in amplitude to increase fuel input.

And in limp mode it sets a constant 1.95ms pulse width.

 

[Goldsburg]

DS4 is constant-beginning variable ending injection system

If this is true, then how does the timing ever advance?

Regards,

 

[Goldsburg]

Also remember that all pumps are designed with specific flowrate and pressure limits - fe, the oem lift pump is designed to pump 4.5psi at 15gph - that means it will pump 4.5psi at 1gph, or 10gph, or 15gph - it will pump 1psi at 17gph, and 0psi at 20gph - doesn't mean it's bad, just that spec'ed ratings have been exceeded

Somewhere in a pumping system is a regulator that sets max system pressure, and may also, due to design, limit system flowrate

In the DS4 6.5 case, there are 8 regulated pressure systems, one for each cylinder, each regulated by the injector for that cylinder - if 7 injectors are calibrated for 1850psi and one is calibrated for 2250psi, the other 7 cylinder pressures do not jump up to 2250psi, nor does the higher pressure fall to the lower pressure of the other cylinders

If 7 are oem injectors and one is a hi-flow marine injector, the other 7 do not become hi-flow systems, nor will the marine become a low-flow version

The injector is the system regulator for it's cylinder, independent (within specs) of the others

In the above cases, engine may tend to run ruff, and PCM may stentoriously object by setting a Cylinder Imbalance DTC at idle

The injector does not regulate system pressure for the entire system. The pop pressure (and pressure just after the delivery valve) at idle may indeed both be the pop off pressure, but as soon as you raise the RPM, the pressure required to move that same amount of fuel in the decreased amount of time REQUIRES that the pressure at the pump increase. The lines are factory sized such that the peak injection pressure for the pump is never exceeded under normal operating circumstances. Start pushing more fuel or exceeding rated engine RPM and all bets are off.

I have seen several twisted pump shafts in the tractor pulling world. These are ALL due to undersized lines and/or injectors for the given flow rate and RPM combination.

To demonstrate that peak injection pressures regularly exceed pop-off pressure, I refer to EXHIBIT A.

Regards,

 

[schiker]

But the clock time of the injection is also variable.
And I believe limp mode also sets a base time.

I THINK the pulse width referred to in that syntex is a measure of solenoid "pulse width" ramp hold and release in total. Not necessarily a solenoid close time duration time only ??? Must be because fuel rate can vary some in limp mode right? Limp mode just sets a base idle, cam time, and restricted max fuel delivery more or less.

In other words I think how fast the FSD closes and reacts is different than the time duration of the solenoid closure event. Again or the speed of the solenoid mechanism.