Quote:
Originally Posted by tomnik
Could you please explain how you intend to grind the cam?
You know that the plunger speed is designed for low speed during filling the element then increased speed during injection and decreased speed closed to the TDC all in relation to the fuel supply bore of the barrel.
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Yes that is correct. Because the 10mm plungers have such an incredible volume displacement per increment of plunger lift compared to the 5.5mm ones, and the comparatively minimal amount of fuel that is required, (even at full power), for my application, the actual required productive plunger lift, (after fill port closure to the point where the helical groove is uncovered ending injection), will be less than .075 inches, closer to .050 inches (aprox 1.9mm / 1.2mm).
If the start of injection, (fill port closure), is at .118 inches, (3mm), of lift, the combined total required lift, (not taking into account the deceleration ramp), would be .193 inches, (4.9mm).
I do not see any benefit in continuing to lift the plunger, pushing fuel out of the barrel, only to have to suck it right back in, creating all kinds of turbulence in the IP in the process and reducing high speed barrel VE.
One way to visualize what I am going to do is to imagine removing the portion of the acceleration lift ramp, between the end of injection, (at full power), to where the deceleration ramp starts, resulting in the deceleration ramp starting at .193 inches, (4.9mm), of accelerated lift. This will allow additional time for the fill port to be open, and, since only the quantity of delivered fuel, (plus any leakage), needs to be replaced, the high speed barrel VE should be improved and turbulence in the IP reduced.
Now because the acceleration ramp is so short, the plunger will not be going as fast as if it were lifted to the full stroke, so I may look at altering the deceleration ramp to reduce additional unnecessary plunger lift, but the 10mm plunger has more mass, so the stock 5.5mm deceleration curve might be good. I have not gotten that far yet. I have designed and developed valve train camshafts in the past, but the geometry of the IP cam is unique. Ill have to through it in the computer and see what it looks like.
Quote:
Originally Posted by tomnik
Next: grinding the plunger? Reducing effective stroke also means taking care of the location of the bore plus adapting this range to the speed/stroke range (cam profile). Are you planning to relocate the supply bore in the barrels?
Tom
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No. I am going to alter the Plunger Helix Angle, leaving the fill port alone. The new angle will reduce the max displaced stroke distance, and spread the fueling out over the entire rack travel range.
Regarding injection timing;
I think I am going to have to grind an angle on the top of the plunger to progressively delay the start of injection as the delivered fuel quantity is increased with rack travel. (I know that is not written well)
Because the injection pulse width is going to be so short, I think the injection timing will have to be adjusted to match the quantity of fuel delivered to achieve the desired pressure curves at different engine loads.
I have found that my 616NA and 617 turbo want as much advance on the bottom end as I can give them, but, as the bottom end torque increases, the top end power suffers because of the additional advance from the advance mechanism, the pressure curve is too high too soon. So I have to back off the timing on the bottom so the engine will start easily and run freely at full power.
5.5mm elements take so long to deliver the fuel at full power that the pressure curve can be relatively optimized with a lot of advance, but with the 10mm elements, 100% of the full power fuel would be injected in less than, (guestimateing here), 10 crankshaft degrees as apposed to 25+ crankshaft degrees with the 5.5mm elements.
Still have a lot of thinking to do, but I want to have the low power, (low delivered quantity), timing around 25/28 degrees BTDC, but at full power, I can see delaying the start of injection to around <15 degrees BTDC.
It should be noted that I am modifying the Prechambers as well, and that the above injection timing guestimets take into account the observed altered Prechamber affects.
The only way I can think to vary the start of injection timing proportionately with the delivered fuel quantity is to grind the top of the plunger, and have the helix angle correspond to end the injection at the desired quantity respectively.
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