Toroidal Combustion chamber design

[rsss396]

Many people shape their combustion chambers in a Toroidal style to increase combustion efficiency.
The basis of the design is to more centrally locate the initial flame to promote faster and more complete combustion.
I have played with a couple heads that were mildly Toroidal in shape and seamed to work very well but have not done dyno testing with them

[jcs003]

this is very interesting.  i wouldnt mind being a test dummy for this.

john

[jcs003]

try this:

http://en.wikipedia.org/wiki/Ricci_flow

john

[rsss396]

john not sure what you are trying to connect with the toroidal head design

[udontknowme]

rsss have you got around to testing any toroidal shapes yet ?  supposedly the style with the plug protruding down doesnt work well compared to other designs. traps burnt gas in the pockets.  

been thinking of cutting a bathtub style if the stock head casting will allow it

[rsss396]

I have not dyno'd the torrid style but have ran it in the field and it seemed to work well. My torrid domes are not cut as deep as some of the domes in the pics. There are some builders on the smaller bores having excellant luck with the torrid design, I have went to the bath tub design because of the dual plug setup I run which IMO also increases the combustion speed much like a torrid design does in theory.
To build a true torrid design with the plug very close to the piston it takes a custom head, the way CP designs there heads it is impossible to drop the plug down enough to make much of a torrid style dome.

With a torrid design its possible spent gasses could linger in parts of the dome but the builders that like them report less ign timing and more power so that would kill that theory because residual gases slow combustion and requires more ign timing to compensate for it

[mennis1971]

Jcs that was like trying to read chinese. Way over my head and yes I did grad college LOL. 4yr Bus mgmt degree, but not engineering. I was OK with math til calculus and I never had any trig either! How I ever passed calculus is beyond me. I must of cheated(not really). Statistics was my favorite, but that was just simple algebra. Sorry for the thread jack, but I was wondering if anyone instantly felt stupid as soon as they clicked that link?

[jcs003]

i believe KTM uses this type of head design.

john

[udontknowme]

ktm makes quit a few 2t in various engine sizes. what type of heads all of them use i dont know. i do know some of the older stuff used standard hemispherical. newer 250 and 300 use bath tube style with no protrusion at the plug area.

250


300. you can see its similar but theres not much radius at the red arrow. not sure the reason behind that. except the 300 is more of a trail bike so maybe that had something to do with it

[ledperformance]

I believe dropping the plug down below the roof could help propagate the flame kernel more evenly through the combustion chamber. How ever I believe the the squish velocity generated by the squish band geometry has more to do with the speed the fuel burns. I am not concerned that there would be pockets of unburned fuel left in that type of combustion chamber. I believe that having the plug more centered in the chamber is a good thing. The flame front has to move fast enough and even enough to not give the end gases time to over heat and flash rather then burn.

[bnau267]

Jcs that was like trying to read chinese. Way over my head and yes I did grad college LOL. 4yr Bus mgmt degree, but not engineering. I was OK with math til calculus and I never had any trig either! How I ever passed calculus is beyond me. I must of cheated(not really). Statistics was my favorite, but that was just simple algebra. Sorry for the thread jack, but I was wondering if anyone instantly felt stupid as soon as they clicked that link?

I was instantly given a headache.  I use a lot of math at work but that stuff was deep.

[Jerry Hall]

try this:

http://en.wikipedia.org/wiki/Ricci_flow

john

Turbulence of the gasses created in the combustion chamber as a result of only the shape of the head is somewhat intuitive. If we are only considering effects from the head shape, the motion of the gases (vectors) present during the combustion process is symmetrical as intuition would suggest.  What really happens in the combustion chamber is more complex than the Maximum Squish Velocity (MSV) calculations that has many of the new engine builders debating.  There seems to considerable debate in this new group over what the optimum calculated MSV number should be. Even if the MSV number was realistic it would be different for different types of engines and applications.  The first time I read about MSV was around 1973 just after the release of an SAE paper that engineers from the McCullough engine plant in Lake Havasu Arizona authored.  Since that time the subject of MSV has been rediscovered, debated, tested and then forgotten a few times.  About every 10 to 15 years this cycle is repeated.  

The vectors in the combustion chamber just before and during the combustion process is a result of more than what the effects of the squish band and the shape of the combustion chamber can contribute.  There is considerable motion of the mixture in the cylinder as the piston approaches TDC.  The motion of the gases are from the scavenging process and from the fresh mixture being pushed back into the cylinder by the exhaust pipe before exhaust port closing.  Some of this motion is damped as the piston approaches top dead center.  As the piston approaches TDC all of the vectors from the various sources are added together to form the resulting vectors present during the combustion process.  The resulting vectors are not symmetrical and all vectors are not moving toward the spark plug as intuition would suggest.

I briefly skimmed over the text and the governing equations from the link on Ricci Flow.  I did not see where it would be much use because of all of the unknown variables that are required for the calculations to be helpful in this situation.  Maybe I missed something in the article that should have been obvious.

[jcs003]

Turbulence of the gasses created in the combustion chamber as a result of only the shape of the head is somewhat intuitive. If we are only considering effects from the head shape, the motion of the gases (vectors) present during the combustion process is symmetrical as intuition would suggest.  What really happens in the combustion chamber is more complex than the Maximum Squish Velocity (MSV) calculations that has many of the new engine builders debating.  There seems to considerable debate in this new group over what the optimum calculated MSV number should be. Even if the MSV number was realistic it would be different for different types of engines and applications.  The first time I read about MSV was around 1973 just after the release of an SAE paper that engineers from the McCullough engine plant in Lake Havasu Arizona authored.  Since that time the subject of MSV has been rediscovered, debated, tested and then forgotten a few times.  About every 10 to 15 years this cycle is repeated.  

The vectors in the combustion chamber just before and during the combustion process is a result of more than what the effects of the squish band and the shape of the combustion chamber can contribute.  There is considerable motion of the mixture in the cylinder as the piston approaches TDC.  The motion of the gases are from the scavenging process and from the fresh mixture being pushed back into the cylinder by the exhaust pipe before exhaust port closing.  Some of this motion is damped as the piston approaches top dead center.  As the piston approaches TDC all of the vectors from the various sources are added together to form the resulting vectors present during the combustion process.  The resulting vectors are not symmetrical and all vectors are not moving toward the spark plug as intuition would suggest.

I briefly skimmed over the text and the governing equations from the link on Ricci Flow.  I did not see where it would be much use because of all of the unknown variables that are required for the calculations to be helpful in this situation.  Maybe I missed something in the article that should have been obvious.

i was merely representing the model.  its not a practical tool but the theory is fun.

john

[udontknowme]

im not sure i have much faith in them msv calculators. if you have .050" squish when the engine aint running how much will you have at 10k rpm ? i dont think them calculators take this stuff into account

[rsss396]

I think MSV calculators are tools to help you gauge where you are at, not a guarantee of performance of the combustion chamber.

When designing a dome and then changing to a different profiles, I believe it helps you make methodical changes.