Ahh, good to know then.

Ken

 

Exactly, but I'm not sure its due mainly to a locally rich or lean region that it fires so well. The rotor face is very, very close to the surface that the leading plug is firing from, and if the leading fires first at anything much earlier than 35* or so, its likely to partially quench the flame front on the rotor surface, whereas the trailing has plenty of room for the flame front to expand outwards and sweep around the chamber with the natural currents in-chamber. There may be some effect at low speeds due to charge inhomogeneity since the leading only fires for a short period of time, but even still, will all the induced tumble (or would it be swirl, depending on your axis), the intake charge would probably be pretty well mixed. What we really need is a fuel flow-meter and dynamometer so we can make some BSFC curves at different equivalence ratios (adjusting timing of course)

 

If you look at flame propagation charts from Mazda showing the effects of leading and trailing ignition, you can see that the leading really only successfully ignites about half of the chamber. That explains why the exhaust is so full of hydrocarbons. Igniting trailing first gets tricky because you don't want to light off the chamber before TDC. At the same time, combustion isn't as effective if the flame fronts from each plug combine before the flame propagation reaches the sides of the rotors. This is a big reason why the 16X is so much better being skinnier. To compound the issue our combustion chamber moves.

The best place from a combustion standpoint would be to place the spark plug right near the center of the rotor at TDC or slightly towards the trailing side. However we then run into the problem of having unequal pressure between chambers that will tend to bleed off into the following chamber through the plug hole when the apex seal crosses it. Basically the same issue that mandates that the trailing plug hole be so small. The truly best place would be where Felix Wankel placed in on the original DKM rotary engine which was a plug in the face of each side of the rotor itself. Obviously we can see the downsides of this but the location was perfect.

It's all just a bunch of compromises. Compression ignition would be the best option but then we run into the issue that air must flow through the dishes in the rotor face rather than staying stationary and being compressed in place such as in a piston engine. Worrying about airflow means that too high of a compression ratio will not allow air to flow through efficiently and will work against us. That limit is somewhere between 11:1 and 12:1 compression which isn't high enough to help us.

We don't have tumble issues to worry about and can't utilize this in a rotary as a piston engine can.

 

...

 

Phil do you have a turbo back on it or is it still n/a? I can give you a stock S4 timing map. Just use a wideband to shoot for around a 13:1 afr across the board and tweak from there leaning a bit at cruising speeds and load. It'll drive pretty good. Then just make sure your ignition dwell settings are good and get your acceleration enrichment setup right which is pretty easy to do.

 

Right now its N/A with an s5 T2 block with a "normal" sized street port and a little exhaust porting.
And the exhaust is very non-restrictive... it's a custom manifold with 2" runners to a 3" pipe
Also, see my other thread at the top, I'm having issued right now :-/