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  #61  
Old 12-03-2008, 02:36 PM
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Originally Posted by GREASY_BEAST View Post
Some people rev the Cummins to ~7000RPM.
Perhaps, but how much fuel that gets dumped in actually burns before it exits the exhaust valve... Very little smoke in PC engines at 5K rpm. How much in a cummins at 7K?
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  #62  
Old 12-03-2008, 04:56 PM
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Originally Posted by OM616 View Post
I think the injector was angled to put the ball back in the spray pattern after the ball was offset from the tube centerline. The ball was off set, per patent doc, to increase the swirl in the chamber.

I think if the angled injector holder is put on a centered ball then the ball will not act as an atomizer. The result could be like an injector with a bad spray pattern.
The drawings refer to the 60x engines. Those PC are different.
The angled 616 PC definitely has a centred ball with the flat turned compared to the "old" version where the flat of the ball points towards the burn hole.
The ball (with its axis) seems to be the same as used in the old version, but the axis is turned, no offset.

Tom
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  #63  
Old 12-03-2008, 06:50 PM
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Quote:
Originally Posted by tomnik View Post
this can be done, but without angling the injector you don't get the defined swirl.
Tom
Actually in patent 4,347,814 the ball is centered and the injector points straight into the prechamber. You will get swirl but it won't be as good as the offset ball and the angled injector.

Edit: (Also note if you look at the patents on google patents you don't have to pay to see the drawings)


Also to all of those that are still eyeballing enlarging the prechamber jets its probably not a good idea. There are papers from NACA that do experiments with prechamber IDI engines. From what I gleaned from them last night changing the restriction will change both peak torque and the peak torques RPM. Enlarging the opening past the optimal size shifted the peak torque to a lower rpm, however it also reduced it.
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  #64  
Old 12-03-2008, 06:55 PM
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Quote:
Originally Posted by tomnik View Post
The drawings refer to the 60x engines. Those PC are different.
The angled 616 PC definitely has a centred ball with the flat turned compared to the "old" version where the flat of the ball points towards the burn hole.
The ball (with its axis) seems to be the same as used in the old version, but the axis is turned, no offset.

Tom

After reading the patent claims while I am awake, I see that only 1/2 the spray pattern hits the ball in the latest patented PC. The ball is .25 to 1.25mm off the center line of the burn tube and the injector is angled 5* in the direction of swirl rotation, but a the patent calls out an acceptable range from 2* to 10*.

I scanned the text and Fig 1 and kept the files big so hopefully they will be readable, the PDF file is too big to attach.

You can go to www.uspto.gov to get the patents. The numbers are in the previous posts. Thank you ConnClark for the patent numbers. Having access to the history behind a part that one wishes to mess with can potentially save many frivolous attempts to improve said part. This is not to say that those of whom, which developed the patented part, did not miss something, or were perhaps confined by stringent emission goals where otherwise different directions may have been taken.

If the ball is not meant to be centered in the spray pattern. Then the idea of swapping parts might work ok.
Attached Thumbnails
Prechamber modifications-prechamber-text.jpg   Prechamber modifications-prechamber-text-001.jpg   Prechamber modifications-prechamber.jpg  
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  #65  
Old 12-03-2008, 07:09 PM
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Quote:
Originally Posted by ConnClark View Post
Actually in patent 4,347,814 the ball is centered and the injector points straight into the prechamber. You will get swirl but it won't be as good as the offset ball and the angled injector.

Edit: (Also note if you look at the patents on google patents you don't have to pay to see the drawings)


Also to all of those that are still eyeballing enlarging the prechamber jets its probably not a good idea. There are papers from NACA that do experiments with prechamber IDI engines. From what I gleaned from them last night changing the restriction will change both peak torque and the peak torques RPM. Enlarging the opening past the optimal size shifted the peak torque to a lower rpm, however it also reduced it.
Good note about google.

Could you post a link to the NACA report. The only one I can find is from the early 30s.

It must be the report you are talking about. Although the engine is vastly different in specks, it does show a relationship between the hole diameter and output.

Advances in technology, even late 70s technology, would change the results of tests were they to be duplicated. However the trends would be similar.

They do state that,

"Air in the cylinder, being distributed over the piston crown, cannot be effectively reached by the unburnt gasses issuing from the chamber and therefore dose not materially assist in the combustion process"

Now it was a 5 inch bore engine, but it does support the use of small holes to jet the gasses throughout the cylinder.

The end of the summary is also grim,

" As the prechamber is inaccessible for scavenging and the lack of clearance under the valves prohibits the use of proper valve timing, the prechamber type of cylinder head is judged to be incapable of developing the high specific output of aircraft engines".

Now it should be noted that this was not a turbocharged engine and the compression ratio was low.
A higher compression ratio will make a big difference in regards to the power curves.

It would seem from the report that a large PC volume with good swirl properties, the biggest holes we can get away with, a lot of boost, and a good camshaft is the ticket. They are all on the list, just one thing at a time.

Last edited by OM616; 12-03-2008 at 09:04 PM.
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  #66  
Old 12-03-2008, 11:37 PM
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can anyone recommend a good single source for the PCs for the 606, 603, 616 (angled injector), and 617.95 besides the dealer?

I found the PC for the 616.912 (old style) for $50-$70, the 617 for $75. I think the 603 was $80ish.

I want to get them to compare and bench test. Plus we will need a source for them to try the highbred set up.
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  #67  
Old 12-04-2008, 03:10 PM
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I don't know how accurate that pic of the prechamber is, but if you look at the volume left in the cylinder at TDC, it's pretty small. The ratio of PC volume to the combustion chamber volume at TDC will tell you a lot about how the hole size will effect mixing. If the CC volume is very small, there's no point in being concerned with mixing as most of the gas is in the PC.
Also, lowering the compression ratio and substituting with boost would be ideal if you could still get it started. I wonder how much PC coating would help with starting.
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  #68  
Old 12-04-2008, 07:56 PM
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I came accost the www.sae.org web sight and found lots of prechamber test reports. Most are for natural gas or gasoline engines, but it does have some diesel reports. I copied two abstracts for an example of the research.

Thermodynamic and Flow Analysis of An Indirect Injection Diesel Combustion Chamber By Modeling

Document Number: 851686
Date Published: October 1985
Author(s):
Ph. Pinchon - Institut Fran\acais du P\aetrole
B. Guillot - Div. of Eng. Res. and Testing, Renault

Abstract:
Two computeur codes, zero and two-dimensional, were used to analyse thermodynamic efficiency and flow characteristics of a prechamber diesel engine. A thermodynamic model was developed and various experimental coefficients were calibrated by measurements performed on an actual automotive engine. Heat release in the prechamber and the main chamber was thus computed. This was found to improve as engine speed increases and to be highly sensitive to injection timing. The poor efficiency of an IDI diesel compared to that of a DI diesel can be explained especially by the high heat-transfer level in the prechamber. Passage loss at the transfer orifice is comparatively less and almost independent of load. Moreover, combustion timing, which is necessarily fairly late in the cycle, has only a small effect on overall losses. Under such conditions, assuming that the technological obstacle can be overcome and that the same combustion quality can be maintained, thermal insulation of the prechamber walls has the advantage of improving specific fuel consumption with almost no loss in filling efficiency.
However, since an increase in wall temperature would affect combustion, a two-dimensional code was used to analyse the air/fuel mixture formation process in the prechamber.
An unsteady swirling structure was revealed with a lifetime about five times greater during the compression phase than during expansion. These findings are supported by experimental published results. Injection simulation showed that the gaseous jet was entrained faster by the flow and that a fuel-rich zone was formed at the impingement point of the liquid spray. Thermal insulation of the prechamber walls was simulated by an appreciable increase in wall temperatures. Computing showed great heterogeneity of gas temperature characterized by the presence of high spatial temperature gradients in the swirl zone. However, despite the very great increase in mean gas temperature, there was almost no change in the aerodynamic structure and rotating velocity of the swirl


The Application of Lag-Process in Prechamber Engines

Document Number: 790692
Date Published: February 1979
Author(s):
L. A. Gussak - Inst. of Chemical Physics, Academy of Sciences of the USSR,
V. P. Karpov - Inst. of Chemical Physics, Academy of Sciences of the USSR,
Yu. V. Tikhonov - Inst. of Chemical Physics, Academy of Sciences of the USSR,

Abstract:
The paper deals with the effect of some design and controlling parameters of a prechamber engine on combustion and operation. The lowest delay in the working mixture ignition, the highest rate and completeness of the burning, the widest stability limits for combustion of lean mixtures, the lowest octane requirements and emission toxicity are obtained only within definite changes in prechamber and combustion chamber volumes (2-3%), in the overall outlet channel cross-section area (0.03-0.04 cm\u2/cm\u3 of prechamber volume) and in the air excess coefficient of the resulting auxiliary mixture (0.4 to 0.7), in the wide range of the working mixture air excess and throttling.


The actual reports can be purchased from the web sight.

The first report indicates that thermally isolating the PC would be beneficial in our quest for power.

I was thinking last night that the 1930s tests used a swirl chamber, but called it a prechamber. I have seen other such cases in later research. In the case of a swirl chamber, the hole diameter is critical in creating a differential pressure, and thus a jetting current is created by the pressures equalizing through the small holes.

With the MB prechamber that is not the case. The holes are at the end of a long tube and would have more of a turbulent effect in the cylinder post combustion. Another way to put it is the PC is isolated from the holes via the burn tube. Unlike the SC, which relies on the small holes, the MB prechamber uses the, now cupped and angled, ball that is situated just off center of the centerline of the tube to induce a swirl.

It would seem to me that the faster the inflow through the tube the better the swirl that would be created. Small holes restrict the flow in the tube and have a negative impact on the swirl. MB's use of small holes in their PC is supported by the 1930s test in that the smaller holes ran the quietest. The highest cylinder pressure was reported as noisier.
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  #69  
Old 12-05-2008, 04:40 PM
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OM616,

The report I was referring to was NACA-tn-436

http://aerade.cranfield.ac.uk/ara/dl.php?filename=1932/naca-tn-436.pdf

I'll post more on this later but right now I'm in a pinch for time.

Until then here is a few things I have learned from reading stuff written by Harry Ricardio (the inventor of the prechamber and swirl chamber engine)
To get the most out of a prechamber engine you want most of the combustion to occur outside the prechamber. For a prechamber engine to work correctly you must have a restriction of flow. There is an optimum speed of swirl. To slow and there isn't enough mixing. Too fast and heat is scrubbed of to the chambers walls.
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  #70  
Old 12-06-2008, 12:55 AM
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Quote:
Originally Posted by ConnClark View Post
OM616,

The report I was referring to was NACA-tn-436

http://aerade.cranfield.ac.uk/ara/dl.php?filename=1932/naca-tn-436.pdf

I'll post more on this later but right now I'm in a pinch for time.

Until then here is a few things I have learned from reading stuff written by Harry Ricardio (the inventor of the prechamber and swirl chamber engine)
To get the most out of a prechamber engine you want most of the combustion to occur outside the prechamber. For a prechamber engine to work correctly you must have a restriction of flow. There is an optimum speed of swirl. To slow and there isn't enough mixing. Too fast and heat is scrubbed of to the chambers walls.

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.

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.

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.

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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  #71  
Old 12-06-2008, 01:21 AM
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Some germans use different PC in the 240Ds that come from the 4 banger diesel trucks heads to get a whopping 5 more hp so they say. So you are on the right track me thinks
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  #72  
Old 12-06-2008, 02:44 AM
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Quote:
Originally Posted by OM616 View Post
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.
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.

Quote:

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.
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.
Quote:
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.
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.
Quote:

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.
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.
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Last edited by ConnClark; 12-06-2008 at 02:54 AM.
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  #73  
Old 12-06-2008, 03:54 PM
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[quote=ConnClark;2040747]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.

In regards to a PC to SC comparison yes.

"In the stock OM617 prechamber, the stock impingement pin splits the air stream and creates two swirls of equal magnitude spinning 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 fairly good."

Yes, hence the off set ball performs better than the inline one.

"Enlarging the holes will only reduce the velocity of the jets blowing into the main combustion chamber, thus reducing mixing and combustion there."

Every test I have seen, including the 436 report (the report I found on that series of tests was #577), has supported my thinking by stating in some form or another that any unburnt fuel that makes it to the cylinder will not equate to any additional power, just high EGTs.

"This will reduce your low end torque."

The 436 test report indicated that the holes should be sized for the highest RPM and load as the lower speeds seemed to be not effected.

But as you and the reports have indicated, if the hole dia is to big then the efficiency drops and the EGTs go up. If the 616 and 617 engines make max power under 3K, then anything beyond that rpm would result in excessive hole "throttling" assuming that MB has the hole dia sized for max power and not just for quite and effieciant combustion.

Thinking how my EGT reacts, with my 240D at 65mph I can maintain about 650* and is farley slow to increase temp with small load changes. But at 75 MPH I can maintain 800* and it is very reactive to power increases. At 75 MPH the holes are "throttling' too much?.


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.

Yes, we are in perfect agreement on that point. There is a ballence point in hole size vrs displacement, RPM, and load.

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."

I tend to think out loud with out providing foundation for the thoughts.

One of the blocks in my thinking foundation is that we are working with turbo charged engines. For example, if we take my 616 NA engine, the PC Throttling point or volume can be fixed as a NA engine has a farley fixed VE.

Now I take and put a turbo on my 616 (my intention) and increase the VE of the engine. Now what was the ideal throttling point will need to be changed to accommodate the additional air.

For another example of my thoughts, lets say that I drill out the holes 10% too big, resulting in below ideal velocity. If I increase the boost by X percentage the velocity will increase due to the additional gasses creating a higher pressure differential.

When I read about the 603 guys running near 45 lbs of boost, I can not help but think that the holes that were designed for 12 lbs are to restrictive and they are not getting the full advantage of the increased boost, and are increasing there pumping losses.


I guess the procedure to enlarge the holes would to be to increase hole area in X% at a time and evaluate the EGTs, and over all performance ( I think EGTs will be a good indicator if the holes are too big) and increase boost to adjust for the increased hole size if EGTs go up.

If, with higher boost, the EGTs go down and power goes up, we have a relationship that could be predictable. Even if to an extreme one would have to run boost at low speeds, which one of the 603 guys was setting up to do last time I looked. They were running really big VNTs.

Making power with Gasoline is much easer!!!! IMO
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  #74  
Old 12-06-2008, 06:36 PM
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Making power with Gasoline is much easer!!!! IMO
Its easy enough with diesel if you are willing to play with fire (propane)...

Connclark- thats a cool insight about the pressure staying higher for longer at high rpms in the prechamber... where does it come from?
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  #75  
Old 12-08-2008, 03:17 PM
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Originally Posted by GREASY_BEAST View Post
Connclark- thats a cool insight about the pressure staying higher for longer at high rpms in the prechamber... where does it come from?
The pressure comes from the partially burned air fuel mixture flowing through the restriction of the flame tube and jet holes to the cylinder.
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