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George,
That is an interesting concept.
But I don’t think it is even theoretically true. I think if you apply some boundary condition analysis you will come to the same conclusion.
On the contrary, theoretically it is true. It is first year thermodynamics.
The configuration you suggests does not appear to take into account the effects of the connecting rod-crankshaft geometry.
You are quite correct. I was refering to a theoretical perfect engine with infinitely long connecting rods that doesn't suffer from these issues. However, the effects to which you alude to have a negligable effect on the points I was making. (actually, shortening the connecting rod moves the optimal theta PP slightly closer to TDC in a real world engine as the piston accelerates faster from TDC.)
It is not the simple area under the expansion curve that results in the power. It is the correct integration of the expanding pressure curve, with the contribution of each point on the curve a function of sin(theta-crankangle).
I think you are considering torque here rather than energy or power. You need to factor the rotation of the crank shaft into your integral. Then you will get the same result as the simple piston pressure/displacement annalysis.
It is not a desirable design to arrange the combustion event so that the maximum pressure point in the combustion cycle gets multiplied by zero (0=sin (zero degrees) in the integration of the pressure-expansion curve to arrive at the torque applied to the crank shaft.
In our perfect, theoretical world I'm not so sure I agree with you. In the real world it is a different story. Here there are numerous issues, some of which I alluded to in my previous post, that prevent us from achieving perfection.
The two points I was trying to demonstrate were simply that 1) the optimal theta PP is a moving target that is dependent on several factors, including rpm and 2) that theta PP is an indication of the inefficiency of the engine.
Rob
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