Actual Rotary Displacement Request

[vex]

Originally Posted by diabolical1

vex ~

again, in as much as i understand what you have said in your post (i'll still need some time to understand the Otto cycle graph you posted ,

Otto cycle is just the technical term of suck, squish, bang, blow

but i haven't read the accompanying link yet) i can't disagree with what you're saying. in fact, i agree wholeheartedly. i guess the problem with me is that i agree with all the points of view because the lines of comparison are blurred.

however, it still comes down to our individual perceptions on where the lines of comparison (rotors vs. pistons) are to be drawn. i suppose the best thing may be making no comparisons at all, but it's probably not going to happen.

Again, the issue isn't so much of what we're comparing, it's how the displacement is literally calculated. Note that all the links I posted concerning piston displacement use TDC to BDC of each individual piston. We can do the exact same procedure and get a displacement at the end of it, but whether or not it is what individual consider accurate is, as you have said, up for discussion.

i've never thought of the housing surface as one cylinder (sleeve), so that is yet another point of view to consider - and in that context it is quite consistent with 1308. it's new, at least to me it is. i don't see it as any more (or less) right as any of the other points of view.

And I agree. It's completely dependent upon how you read into the equivalences. You could take Rice's approach and claim each rotor face is a piston equivalent, which would net you a the 4L displacement. If however you consider the standard practice of TDC to BDC than you will always only end up with 1.3L (for a 13b). Another way I look at it that makes me lean towards the 1.3L displacement more than anything else is that the actual physical displacement is maintained in the same physical space.

that said, it makes sense with the TDC-to-BDC definition of displacement. the eccentric shaft only allows one TDC per rotor and that would also be the reason why you said the rotor should be treated like a piston. i get that. again, it's not that i reject any of the other assertions, i just find myself gravitating to the 3.9 more than the others.

And that's fine to do--Just be aware that it is not equivalent to the standard practice of engine identification.

for what it's worth, regardless of what i posted before (or in the future) about the 3.9 displacement theory, i do still consider our beloved 13B to officially be a 1.3L powderkeg of fury - just not in an absolute sense. as far as what to consider any of the rotary engines, i believe Mazda's final and absolute determination trumps mine any day and i'm good with that.

Like many bright people have said before; it's all relative.

Originally Posted by Monkman33

You cant "just ignore" the rotation factor. its the only way to create something consistent and precisely equivocal between the two styles of internal combustion engines.

Actually you can. Take a snap shot of a piston in TDC. Then take another one at BDC. The resultant difference in volume is the displacement. You do the exact same thing for the rotor. TDC snap shot. BDC snap shot. Resultant displacement is the difference in volume between the two. There is no need to worry about crank shaft rotation.

If you want to compare the two engine types, you have to have a constant.

That constant is TDC and BDC for all otto cycle engines.

What is more constant than the point that transfers the power from the point of generation to the drivetrain?

How about TDC and BDC since those are constant across all motor types. How would you measure the displacement when you have 3 eccentric shafts operating independently or at different rpm on the same engine? Using your definition you'd have to normalize the entire assembly rather than just look at the discrete values of TDC and BDC (think of it as the limit of integration: Vol_tot=integral(dv,vol_tdc,vol_bdc). Eccentric shaft revolution doesn't play any part of displacement.

If you don't want to compare the rotary to a piston engine, then i feel that 3.9l could very well be more accurate in the aspect that in 3 rotations it does displace 3.9l.

And I agree that if you wish to calculate the combined displacement of all rotor faces that is the number you'll get. If however you wish to remain in standard practice you need only concern yourself with TDC and BDC of each rotor.