Need help with Injector Pump (Minimum Engine Speed)

[veggie]

Hi All,

Is anyone familiar with the internals of the Injector Pump and whether modifications can be made to the minimum flow point?

I have a project where I would like the engine to run continuous at 250 rpm.
The problem is that when the speed is set any lower than 325 rpm, it cuts out !!!
The governor linkage is quite free and I have tried several springs ranging from stiff to very soft.
Even using my hand on the rack plunger I can control the speed closely down to 325 rpm and the engine stops at any point below that.

I prepared a video to demonstrate.
You will note that as the engine speed hits the current setting (325 rpm) it cuts out, then as it slows below the set point the governor gives a small tug and the engine fires with a thump to bring it back to 325. Then the injector pump stops fuel flow and the same cycle repeats. You will hear a thump every several revolutions as the engine fires and then cuts out to coast again.
https://www.youtube.com/watch?v=n8ZdIOONaOU

I have seen many engines running at very low speeds. So I know it's possible.
Such as this one...
https://www.youtube.com/watch?v=4jTxVD5Vaas

Any ideas for modifications

[38ac]

As seen on the other video you should be able to bring it down much slower than what you are able to achieve. I have not seen that issue previously so all I can offer is guesses.
Helix cut wrong in pump element
Cam timing and lobe placement is such that the adjustment  bolt must be set extremely high thus the element isnt dropping low enough at low delivery.

And grasping at straws
Worn element is bypassing fuel at low deliveries
Injector pop off set too high to pop at low delivery
Injector pintle is stuck partially open or not seating a dibbling.

[veggie]

Thank you 38ac,
It looks like the only thing I can alter in that list is the pop pressure.
I can loosen the injector spring tension screw by 1/4 turn at a time to see if that makes any difference.

38ac: "Cam timing and lobe placement is such that the adjustment  bolt must be set extremely high thus the element isn't dropping low enough at low delivery."
Is this something I can adjust/control ? If so, how does one set this?

[mihit]

I am familiar with the internals of the IP, couldn't tell you for sure, but I'll speculate.
The main doo-dad (spindle that sits inside the collar that is acted on by the toothed governor bar) has two "holes" that are joined by a slanted slot. When at minimum fuelling only the idle hole can flow, when it's WOT both holes are lined up and fuelling along the slot.

At a guess, the options for rebuilding this would be find another collar and move the holes so that fuelling is achieved earlier on the rack, or find another spindle and modify the spacing/shape/width/length of the groove to allow greater fuelling.

But you could just call it a Hit'n'miss lister!

Other option I'm guessing is governor weights, play around with them so it doesn't throw out so easily... depending on how you want/need to load the engine.

What is actually the point in wanting to run so slow? Surely you're sacrificing half or more of the HP it would have...

[38ac]

As you likely know the injection timing is adjusted by the bolt under the pump. I have seen India engines where the cams were installed a tooth off and thus to get the injection timing right the bolt must be set very high. Seen them high enough that it pump was actually bound up and the high point. The easy way to check is to turn the engine until the lifter is down  and loosen the pump bolts. If the pump is shoved up more than a small amount,, maybe 1/8" the lifter is set high enough to bind the pump.  I'd bet on the pump element helix is cut wrong ,,, interesting problem

[veggie]

Thanks for the suggestions gents.
I will dig into the IP components and see what's going on.

cheers

[cujet]

Do you have another pump to try? Possibly the pump position that would result in 200 RPM, produces no fuel?

I'm going to go out and run my engine and see how slow I can run it. I'm pretty sure it will go down to a very low RPM. Checking now.



Update: Tried low RPM by pulling up on the shut off lever. The not warmed up engine was 100% unwilling to run at low RPM. I could hear the injector's clank, so I'm pretty sure it was working. After warming it up, I tried again. The engine would maintain low RPM, but only fired every other time. Even though the injector clanked every time. The engine was difficult to control at this speed, and would occasionally need an open rack to get enough fuel to initiate combustion. Eventually, it slowed down to the point where the injection event brought the engine to a fast stop-n-reverse. At which point I engaged the compression release and the thing rolled backwards for a bit.

That 200 RPM video you posted did not seem to have much of an audible combustion event, and the RPM seemed very even. Mine would speed up and slow down around each combustion event.

Thinking aloud here, it's entirely possible that the compression is insufficient to ignite a tiny fuel quantity, and/or the indirect chamber has insufficient oxygen in it. Hence the 8 cycle running. I really do think the injector is working, as I can hear it.

If the Indian video is real, maybe they have higher compression or adjusted the timing to be closer to TDC, so the engine won't reverse like mine did.

[veggie]

cujet,

Thanks ! That was very helpful.
You seem to have achieved the same symptoms as me.
It could be that these engines simply don't run very well below 300 rpm.

My project of running 24/7 at very low rpm may still work at 350 rpm instead of 250 rpm. At 350 my engine runs steady without missing a beat.
The idea being that during a power failure, this engine will very quietly PUT...PUT along at low speed driving an alternator at 24 Volts / 15 Amps.
At times it will surely fall behind the demand, and at other times (through the night) it will exceed the demand.
The battery bank will buffer the power usage.
I did the math and based on my demand of furnace fan, some lights, refrigerator, and freezer, it should work fine.

Thanks for testing that.

Anyone else care to join in the Lister(oid) low speed test and report back ?   

How Low Can You Go ?

[38ac]

I have had several down slower than you can achieve but never really tried to see how slow one could run. I don't have any runable singles here right now but will have a 6/1 done soon. I did go out and fire up my DES 16/2 and it will go down very slow and hit every time. I'll try to get a video one day soon 

I would be worried a bit about cylinder lubrication at 250 rpm. Maybe turn the slinger sideways? And keep the oil plenty high

[38ac]

Here ya go Veg, a short clip of my 16/2 running purdy daggone slow. Engine was stone cold, started it, grabbed the shut off lever to slow it down and grabbed my phone. I was surprised that running this slow that it was still running on both cylinders, guess the builder did a good job of syncing the fuel pumps! LOL

https://youtu.be/xtAY8_nbksU

[starfire]

my 3/1 struggling cold on vege oil
https://www.youtube.com/watch?v=Hc3dXaBPpvw
theoretically a twin should run slower having twice the firing strokes,  a heavy flywheet model would run smoother at low rpm. Vege oil i suspect is possibly more reluctant to combust than diesel or kero, so possibly skipping a few bangs here and there. Also compression pressure would play a role too.

[38ac]

Yes two firing strokes but also the same flywheel weight as a 8/1 single but carrying over two cylinders firing only 90 degrees apart.  Watch the flywheels slow down dramatically as number one comes up on compression.

Your 3/1 is firing every other stroke as it should.  Veggies issue is interesting and I am curious to hear what he finds out is causing it since Cujets engine does the same thing

[veggie]

38ac and starfire, you definitely achieved SLOW RUNNING. 

I have a theory.
My engine is a 900 rpm 8HP unit.
Is it possible that the helix cut in the rack is machined for higher speed/HP sacrificing a few hundred rpm at low speed.?
(as compared to a 650 rpm helix)
I chose not to dismantle the injection pump. Rather I will check the spill timing and play with the injector pressure.

 

[veggie]

starfire,

I looked at your other lister videos. Very nice setup in that shed. (looks like a lister/petter unit off to the side also).
Would it be possible to post a picture of how you mounted the alternators to your engine?
I have a similar plan in mind.

cheers,
veggie

[cujet]

38ac and starfire, you definitely achieved SLOW RUNNING. 

I have a theory.
My engine is a 900 rpm 8HP unit.
Is it possible that the helix cut in the rack is machined for higher speed/HP sacrificing a few hundred rpm at low speed.?

Mine is a 6/1 that has been uprated by simply speeding it up. (and smaller dia flywheels) 

If you pull the injector, I'm sure you can watch it spray at low RPM. Of course, that's not overcoming compression, but it will answer the pump question. Mine has a starter motor which seems to crank it over at an RPM the engine should be able to "idle" at. I may try the injector thing and see what happens (I have spares)

However, because my engine is clearly "8 stroking" at low RPM, I'm pretty sure the fuel is getting into the combustion chamber and simply not igniting until a "double batch" of fuel is in there. I can check this a bit by locking the fuel rack in the (8 stroke position) and using the starter motor to start it. If, when I move the compression release, I get a single large pop, followed by no running, I'll know something more.