Hi!

I was thinking is it possible if we change the opening pressure of the injectors we can control the amount of fuel injected. I.e. the opening pressure of the injectors of an om602 turbo is 135-145 bar when new and at least 120 bar used. If I lower it to lets say 100 bar, the injector will stay open longer, thus injecting more fuel. The injectors of a n/a 601/2/3 engine have a factory opening pressure of 115-125 bar when new and at least 100 bar when used, thus 100 bar should be acceptable.

Is this idea flawed or not?

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

It don't work that way...the lower pressure will inject slightly earlier...the injection pump determines how much fuel...being as fuel is nearly incompressible the i/p pushes the fuel and it don't matter if it was 170 bar the fuel quantity will be the same for that throttle position.

However, the engine will be a little quieter.

Bosch uses that 120 to 135 bar setting primarily to inject a mist of fuel rather than a squirt or large droplets that would not completly burn.


.

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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

I agree that the ip determines how much fuel is going to the injectors, but there's excess fuel otherwise there wouldn't be any need for fuel return hoses. If there's fuel returning from the injectors it means that not all the fuel is being injected. Is this correct?

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

Yes....and no. Injectors are not sealed internally like gasoline injectors are. and some leakage is designed in to lubricate the pintle. The amount NOT injected is so small as to be of no account.

The only way to inject more fuel is to move the rack further toward full load position or increase the size of the i/p delivery plunger barrels.


.

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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

If the injector opening pressure was lowered it would inject slightly sooner; it would also mean that the injector would also close sooner per the same volume of fuel. So I think that the amount of time the injector would be open would be the same regardless of the injector opening pressure.

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84 300D, 82 Volvo 244Gl Diesel

Hi,
changing the opening pressure will change the injection timing.
This must be corrected. The only method to do this is with a dynamic timing device. Due to wvo I increased the opening pressure to 175 bar (better atomisation, less smoke, better efficiency). The timing went 2-3 deg. retard.
The duration of injection, starting from the correct beginning of delivery, should be rather shorter to stay away from TDC to avoid unburned fuel delivered too late.
Increased duration can be achieved by turning the full load screw which will result in black smoke, because this additional fuel (the last part) comes too late and can not burn completely.
The one and only thing to handle this is larger elements.
Starting at the correct beginning of delivery the same quantity of fuel is injected in a shorter time and can burn completely, better efficiency! And/or a larger quantity of fuel, but injected in the same period of time (duration), burning completely, depending on sufficient air, will give extra power without black smoke.
Even with stock air supply it works well! Both efficiency and performance.

Tom

Lower pop pressures will yield more fuel, but it will increase the duration which is bad. The reason it will give more fuel (according to theories bounced around on the various chat boards) is that although the fuel is virtually incompressible, the lines flex. Thus, a higher pop-pressure will result in less fuel exiting the nozzle and a shorter duration. Lower pop pressures will yield longer duration and maybe a little more fuel, but it will have the extremely detrimental effect of altering the spray pattern and reducing atomization.

A much better and probably more effective way to get more fuel (without doing costly pump re-designing or shipping things to Europe) is to remove/reduce restrictions between the IP elements and the combustion chamber.

One of these restrictions is the delivery valve collar.

Another is the injector tip.

Removal of the delivery valve collar has resulted in massive fueling increase
Injector enlargements have proven massive power gains in other engines.

All with no pump modification.

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99 E300 Turbodiesel 100k

I like that tomnik had some evidence due to the dynamic timing device to support what he said.
To prove that lower injector opening pressure yields more fuel injected I would like to see the IP on a test stand and the fuel quantity measured at the high pressure (maybe about 10 test runs at that pressure) then have the same injector adjusted to a lower pressure and the IP run again (for another 10 test runs) and fuel quantity measured again and compared to the first measurement.
The variables could be the fuel that leaks by the injector pintel and the IP elements (plungers and barrels) which is needed for lubrication. A higher injector opening pressure might cause more "leak by" in those areas.
Is this enough to justify lowering the injector opening pressure just to get that tiny bit of fuel more and loose the benefits of the higher opening pressure?

The injector hard lines swell under pressure so some fuel is lost due to some of the fuel quantity being still in the injector hard line when the nozzle closes. So higher injector opening pressure = slight uninjected fuel loss.
I do not think so. As soon as the nozzle opens the pressure is relieved on the injector hard lines witch would return to its unexpanded size because the hard line is not a springy as the nozzle spring it will return to its shape fast. Try it with your garden hose and a nozzle with a shutoff.
When shutoff the hose is swollen; when the nozzle is opened the swelling goes away.

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84 300D, 82 Volvo 244Gl Diesel

So lets summarize:

1. Do we agree that lowering the opening pressure of the injector will lead to more fuel being injected?

Why? Because the injector starts injecting earlier when set to lower opening pressure and will keep injecting longer than an injector with a higher opening pressure. As far as I know this is how people increase the amount of fuel in common rail engines. They either increase the common rail pressure or keep the injector open longer.


2. We all know that higher pressure means better atomization, but 100 bar seems to be acceptable even by Mercedes. So by lowering the opening pressure to 100 bar we are allowing more fuel in while still being within Mercedes standards.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

You've only thought about half the event. The event goes as follows:

1) Plunger rises
2) Injector line swells
3) Injector opens
4) Injector line contracts (depending on pressure relief through nozzle)
5) Injector closes
6) Injector line swells
7) Plunger descends
8) Injector line contracts

You made it to step 4.

With higher pop-pressure (more spring tension in the injector body due to thicker shim) the injector closes sooner, thus causing the line to swell and not allow as much fuel in. Keep in mind that even with only 5psi in the line, the line DOES swell, just not very much. Therefore, if you increase the pop pressure, the line has more volume when the injector closes, therefore, because the plunger only pushes a finite volume, the line "absorbs" a greater quantity of the fuel.

Again, this is all completely theoretical and if you really want to find out anything meaningful, dyno testing is probably the best method.

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99 E300 Turbodiesel 100k

Hi,
I do not agree. I tried the hard lines out of the 60x engines without any difference.
These lines are smaller in diameter and my intention was to get better response of the pressure wave towards the nozzle. In my opinion compressibility of fuel and swelling of hard lines is there but recognisable only at extreme pressures > let’s say 500 bar. The CR stuff works with pressure ranges up to 1500 bar using huge volumes (rail) and identical hard lines, little shorter in length but same id and od.

More important for me is to start thinking at the nozzle. Even if there is more fuel at lower pop pressure this additional fuel will burn incomplete so there is no gain.

Restriction in fuel flow: The volume flowing is very small, then interrupted by closing of the nozzle. For me the accurate stop and go of the fuel column seems more important than just pumping fuel. There is a lower limit of pop pressure where the atomisation is too bad to get the car running well, never heard that turbos run better with na injectors but on the other hand that increasing pop pressure reduces smoke.

With our ip the amount of fuel is determined by the effective stroke of the plunger and the nozzle, set to a specific pop pressure, can only release the quantity coming from the ip. In theory: Run the ip without injector, just the hard line or even without delivery valve. The quantity is limited to the geometry of the element. The quantity being delivered out of the diameter of a hard line (theoretically huge nozzle) will not spray.
Garden hose with 3” id but the supply from the water pump remains the same.

The CR and gasser things work with a continuously pressurised system and the injectors determine the quantity for the injection. In this case bigger nozzles make sense but not in our system.

The delivery valves have an orifice to kill the back pressure wave when the nozzle closes and the IPs with 10mm elements have similar DVs. On top of this the C111 engine was not modified in injectors, hard lines and DV. Next thing they would have touched is the prechambers…

Just my thoughts, sorry for the long text.

Tom

Are you 100% sure? The pump they used was a custom build, nothing ever seen on a production engine.

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that's what I was told.
hard lines are the 61x ones, injector (bodies) are stock...
Up to almost 90 ccm fuel delivery on the bench I could not see any restriction in flow, this was also the estimated quantity out of the calculation, more or less.


tom

I was not describing all the steps it took to inject the fuel; I picked things that I believe would change the fuel quanity if the pop pressure/opening pressure if the injector nozzle would possibly effect.

1) Plunger rises- The pluhger rises but will not start injection fuel until the fuel feed port/hole in the side of the element is closed (causing the begin of injection/port closing). The begin of injection depends on what position the "Helix" on the plunger is in.

6) Injector line swells- The injector line dose not swell again as the delivery valves have a portion on them that produces "fuel retraction" in the fuel lines which causes an abrupt cut off of the fuel and even pulls some fuel backwards to. Partly to cut off the fuel abruptly and decrease the pressure wave. The result is that there should be no swollen hard line.

7) Plunger descends- Ounce the delivery valve closes (this happens before the plunger decends) the decending plunger has no effect on what is going on in the injector hard lines.

8) Injector line contracts- Again when the delivery valve closes the the injector hard line is already contracted due to the fuel retraction feature built into the delivery valve.

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84 300D, 82 Volvo 244Gl Diesel

just a detail:
begin of delivery is always the same. END of delivery depends on the helix.

Tom