Pre combustion chamber design research

[Rockabillyrat]

Hopefully I am not going backwards, I am having a set of the military triple square ID ones opened up to match the diamond just on the opening no machine work to the internal side of the cup, Head gasket to lower compression to 18:1 or so.

We haven't done the testing to prove which cups are better yet. But though everything I've posted here and tons of other stuff I've been reading. I dont see a reason to run bigger cups at all. Every one always talks about bigger cups can flow more fuel. Well even if your pushing 300cc of peak fueling. That's only .3cc per injection event. Small cups can handle a mouse fart amount of fuel. The big factor is going to be getting a pressure transducer in the prechamber and seeing what effect each cup has at a given RPM. The only benefit I could see with bigger cups is the ability to be less restrictive at high RPMs. But that restriction is needed for atomization of the fuel as it leaves the cup. Alot of testing to come. I'm behind schedule on where I want to be. But this is still very much in the works. Just need to let my bank account recover after dropping some serious cash on a bullet proof rotating assembly from TSP.

 

[dixiepc]

Any new information?

 

[Rockabillyrat]

Nothing yet. This summer has been a wash out as far as me getting anything done on the truck.

 

[dixiepc]

This is the kind of stuff I like to see.

 

[Rockabillyrat]

Me too lol. There is alot of testing coming down the road. We plan to fully prove or disprove all the theories on cups, injectors, compression ratio, ect.

 

[Twisted Steel Performance]

So you have access to a engine dyno ??

 

[Rockabillyrat]

So you have access to a engine dyno ??

We are looking to rent one. But if we can find one for sale at a reasonable price. I would like to go that route. With the amount of testing to be done. It would probably be cheaper than renting one constantly.

 

[Twisted Steel Performance]

I know where one is new still on the pallet, ( for 2 years now ) I will see if it is for sale or not...

 

[Kaulin C]

To my surprise and great pleasure I found a thread on GM diesels that is less than a decade old. I'm glad to see there are still lots of enthusiasts looking to find design improvements on these engines.

The main topic of this thread, precup geometry, is what led me here. Over the past couple weeks I had been doing some browsing on the internet trying to learn more about the specifics on how the precup affects combustion in an IDI. Currently being a ME student, I have access to particular documents that would typically be blocked to most. Here is one article I came across from 1984 and thought was interesting. I wouldn't be surprised if RR has already seen it, but it's a good read anyway. Angle inside the precup as well as the angle of the precup exit affect the combustion.

 

[Will L.]

Welcome Kaulin.

 

[n8in8or]

Welcome Kaulin and thank you for sharing that document! Any others that you come across that you would care to share I think we would all love to read.

 

[Rockabillyrat]

Thanks for sharing! That's one document I haven't seen yet.

 

[MrMarty51]

To my surprise and great pleasure I found a thread on GM diesels that is less than a decade old. I'm glad to see there are still lots of enthusiasts looking to find design improvements on these engines.

The main topic of this thread, precup geometry, is what led me here. Over the past couple weeks I had been doing some browsing on the internet trying to learn more about the specifics on how the precup affects combustion in an IDI. Currently being a ME student, I have access to particular documents that would typically be blocked to most. Here is one article I came across from 1984 and thought was interesting. I wouldn't be surprised if RR has already seen it, but it's a good read anyway. Angle inside the precup as well as the angle of the precup exit affect the combustion.

I did pretty good on the reading until I came to the math equations that had alphabets innum. LOLOLOL
Welcome to the truckstop Kaulin.

 

[Rockabillyrat]

It's been a while since I've posted in here. But my research still continues. Mostly I've been focusing on injection pumps. But I wanted to share some precup related stuff I forgot about. I took pictures of the diamond and square cups and compared them to the channel in the piston. To me it looks like the square cup does a better job or concentrating the flame front into the channel. And the diamond cups may spread the flame front out side of the channel.




This last picture is a used piston that was running diamond precups. You can clearly see the witness mark the flame front left on the outside of the channel. Now this wasn't my engine so I can't confirm if it have thicker head gaskets or not. But it was definitely a diamond precup. I would imagine thicker head gaskets would widen the flame front due to the increased distance between the cup and piston. But I can't confirm that's what happened here. In my opinion the distance between the cup and piston should not be changed for this reason.,

 

[dixiepc]

It's sure gonna be nice to see some dyno results.

 

[Rockabillyrat]

Dyno numbers are only a small part of what I'm excited about. I cant wait to get a pressure transducer on one and seeing what changes cups, injectors, and timing make on cylinder pressures. That will be the key to getting a 6.5 to live.

 

[Kaulin C]

I would imagine thicker head gaskets would widen the flame front due to the increased distance between the cup and piston.

It is probably the diamond precup causing the wide burn mark there. According to this diagram from the above article, a tighter piston to head clearance makes the jet spread out faster (hc is head clearance here). Imagine the way a bead of silicone spreads out when it's squeezed between two surfaces.

 

[MrMarty51]

Oh for a four valve, dual injector head and piston for our old beasts. LOL
I guess it might work the same as machining the heads on a Shovel Head Harley to dual plugs. LOLOLOLOLOL

 

[dixiepc]

Come spring I'm gonna pull my engine for a refresh, head studs, timing gearset, and a new Bull Moose pump. While I'm into this I'll have to make a decision on squares or diamonds. I have diamonds on now but I have 3 sets of Optimizer heads with squares. Want to use the best ones.

 

[Will L.]

The problem with knowing which would be better is a person has to build and dyno, then yank heads, only change the precups, and dyno agian. No other changes.
So really you want an engine dyno, not a roller dyno.

And while you can do it and learn which is better for your set up, it may be different for someone with a different injection pump, different injectors, etc.

Have any dyno spots near you? I’d like to see a heads up comparison of only cup swap enough to kick in a few bucks.