Turbo20V
Mechanical
- Jan 12, 2010
- 10
So I have been thinking a lot about the mathematical optimization of cylinder geometry lately.
I seems as though the intersection point of flame-front propagation and the dynamic stresses for a standard gasoline engine yield a cylinder volume of around .5 liters.
Obviously low speed engines can have larger cylinder volumes because there is more burn time, and conversely high speed engine operation can only sustain small cylinders.
Now since most modern cylinder designs are 4v the spark plug is located at the center of the combustion chamber, and the flame-front propagates radially from that point.
Is there a formula that predicts the combustion front velocity?
What about the heat? how does the heat develop as a function of combustion and time?
The pressure in the cylinder I assume is a function of the base pressure at TDC, and the heat of combustion as it causes the air to expand.
Now I do understand that this is multivariate, and non linear. There is certainly a lot of things going on. However I think it all boils down to this:
You have a radius of combustion. The spark happens and the flame-front rushes to the sides. Combustion is exothermic, heat is generated. The heat energy expands the volume of the gas. Dow during this process the piston is moving down, so the volume is changing in a nonlinear fashion.
Does the complete combustion happen over a relatively small crank angle? I imagine at low speeds it does, but what at high speeds? 6000-8000+ RPM? How much crank angle change happens during that combustion time?
I would imagine that engine developers have modeled this fully, however the raw results are often obscured by race regulations.
Anyone have any insight on this? Actual combustion design experience?
I seems as though the intersection point of flame-front propagation and the dynamic stresses for a standard gasoline engine yield a cylinder volume of around .5 liters.
Obviously low speed engines can have larger cylinder volumes because there is more burn time, and conversely high speed engine operation can only sustain small cylinders.
Now since most modern cylinder designs are 4v the spark plug is located at the center of the combustion chamber, and the flame-front propagates radially from that point.
Is there a formula that predicts the combustion front velocity?
What about the heat? how does the heat develop as a function of combustion and time?
The pressure in the cylinder I assume is a function of the base pressure at TDC, and the heat of combustion as it causes the air to expand.
Now I do understand that this is multivariate, and non linear. There is certainly a lot of things going on. However I think it all boils down to this:
You have a radius of combustion. The spark happens and the flame-front rushes to the sides. Combustion is exothermic, heat is generated. The heat energy expands the volume of the gas. Dow during this process the piston is moving down, so the volume is changing in a nonlinear fashion.
Does the complete combustion happen over a relatively small crank angle? I imagine at low speeds it does, but what at high speeds? 6000-8000+ RPM? How much crank angle change happens during that combustion time?
I would imagine that engine developers have modeled this fully, however the raw results are often obscured by race regulations.
Anyone have any insight on this? Actual combustion design experience?
