Originally Posted by NoDOHC
Correct me if I am completely mistaken, I will try to explain the figure.
The diagonal lines indicate the position of each component as the rotor rotates.
The angle indications are in rotor degrees, not eccentric shaft degrees.
I believe they are in shaft degrees.
The distance from the left indicates degrees of rotation when that region of the chamber burned.
The different lines are the different ignition timing settings that clearly cause significantly different behavior.
X is observed through a quartz window, O is taken from an ion plug, and the other two are calculated.
The trailing side (due to squish influence ) seems to be the weird one, the flame front displacement seems to shift nicely for all points below the leading plug.
It looks like the flame front is traveling forward just fine, it is the backward part of the curve that confuses me. This would seem to indicate the the flame front follows the rotor rather than the housing (which makes sense, the rotor has the dish).
We should think of the mixture flowing like a river and ignition spacing like dropping two rocks into it. Each wave travels downstream easily, upstream not so well. But what happens when the two waves collide? This interaction slows the flame speed (notice the dogleg in the LL at the bottom of the graph).
I think I see why it knocks right above the trailing plug, the flame front actually reverses direction there (although not relative to the rotor). This must be right at the quench boundary at the edge of the rotor dish (probably when it meets the cusp on the housing).
Do you know what the engine speed was for this test? Do you know the manifold pressure? (I would guess NA).
The X Measurments were done through Quarts windows NA at 1000rpm.
It appears that at 20 BTDC (ATDC?) , the leading front has basically dissipated by 45 degrees (Eccentric shaft, 15 rotor) (which makes sense why you observed the highest pressures when the peak occured at 45 degrees)
Here is a theory about what is causing your knock on too much timing advance. Knock is typically caused by some shock wave colliding with the flame front (it can be a second flame front). My thought is that the leading and trailing sparks both touch off the mix in the chamber if the timing is advanced too far, this results in the two flame fronts colliding while they are stil moving very quickly. To test this, you could try unplugging the trailing plugs or adjusting the ignition split and observing what difference it makes.
This research is awesome. Where did you find that diagram?
This is from a Mazda paper Rotary86v6a4, Fig. 14, showing flame propagation.
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