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Originally Posted by OM616
Same test,
The report that I found was for that series of tests on that engine, but the results were used to evaluate a prechamber engines ability to produce enough power for an aircraft.
As I said in my evaluation of those tests, the engine being tested had a swirl chamber, which is different from the MB Prechamber. Apples to oranges.
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Its not apples to oranges. Its more like comparing a macintosh to a golden delicious. A swirl chamber is a prechamber combustion engine. Its just a more efficient form of one.
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I also had the thought about the configuration of the MB prehcamber. There is the chamber, then the tube, then the holes. The air has to go in the holes first which creates turbulence at the bottom of the tube but not in the chamber, then the air flows up the tube at a velocity that is regulated by the hole dia and the TUBE dia. The air enters the chamber at X velocity and is directed by the bottom of the ball into a swirl rotation.
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In the stock OM617 prechamber, the
stock impingment pin splits the air stream and creates two swirls of equal magnitude spining in opposite directions. (see attached picture) This doesn't mix as much fresh air past the combustion zone as a swirl in one direction but it is faily good.
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I now think that the inside diameter of the MB tube would be comparable to the dia of the SC hole that was tested. If that is right, then if the burn holes were opened up, the velocity of the tube air would go up and create a stronger swirl as well as allow a higher PC air content. Picture if you cut off the tip of the MB PC removing the holes, what you have left is a SC with a ball at the chamber end of the tube (hole). Apples to apples in that case.
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Enlarging the holes will only reduce the velocity of the jets blowing into the main combustion chamber, thus reducing mixing and combustion there. This will reduce your low end torque.
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As I get the impression that you are not a fan of increasing the MB hole dia, I am very interested in your thoughts. Apposing arguments are vital in this discussion of theory.
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The restriction is an essential part of the operation of a prechamber engine. It keeps the pressure in the prechamber higher for longer at higher rpms where in a conventional diesel the falling piston drops the pressure quickly and thus reduces burning efficiency. The prolonged higher pressure also keeps the burn rate high.
You are new to the concepts of this design and many are counter intuitive. Keep digging through the NACA archives and read everything you can find on diesels. Then get a copy of "The High Speed Internal Combustion Engine" by Harry Ricardo.
You will soon learn the quirks of this design.