madaz matt

After thinking about welding the rotars and the shape of the combustion chamber could you use water injection to up to compression instead??? or even beter 50/50 water methanol

diabolical1

not really sure what you're asking here, but i'll put it like this. if you're talking about a turbocharged rotary application, it will allow you to run more boost by virtue of it's use as an anti-detonation tool. so i guess that means you're increasing dynamic compression in a "loose" sense - more boost (air) compressed in the same chamber volume.



however, it has no effect on static compression numbers.



is that what you're asking?

madaz matt

yes im after rasing static compression for N/A use i heard that thay use to do that with some piston engines. then you could use it like a turbo if you set it up on a rpm scale (more rpm more water) or like nitrouse with a push button. this has to have some effect on compression.

diabolical1

okay, i saw your other thread. i think i see what you're after. well, i'm not touching the issue of getting a static compression greater than 10:1 (the highest of what's already available from Mazda), i think you should use what's available because i'm sure there's a reason that things are the way they are. i'm sure greater minds have thought about it, but one issue or another has led to not acting on the idea.



however, to address your question, i guess on a technical level, then yes ... water injection (or a slower/cooler burning fuel choice) might be a tool utilized to fight the higher combustion temps and detonation. of course, this is said with the assumption that you're not trying to substitute it for better tuning.

heretic

You would need so much water to affect compression ratio to any useful degree that combustion would be snuffed out.



We're talking on the order of ccs per chamber. Even at say 2cc of water per chamber, which will affect compression very slightly, we are talking about 4xRPM cc per minute. At 10,000rpm, which I recall is a level you're concerned with, that is 40,000cc per minute. Combustion generally stops when water is injected at twice the rate of fuel, so we're well beyond that. You would also need a way to get a liter of water into the engine every 1.5 seconds, not to mention having a tank large enough to store it all.



2cc per chamber would change the compression ratio in an RX-8 engine from 10:1 to 10.25:1, for what it is worth.

sureshot

The short version:



Filling the rotors is counter productive for many reasons.

Controlling structural stresses.

Rotational balance of the rotor.

Chamber volume balance.

Rotating assembly balance.

And - making an already non optimal combustion chamber shape even less optimal.



If you want higher compression - switch to renesis rotors & counter weights.



For simply more power - get it to breathe, (a good port job with good standing wave resonance in the runners.)



Water/alcohol injection will allow more advanced timing, which can yield more power.

heretic

Operative word here is "can", of course.



It is entirely possible, and not all that uncommon, for timing to be power limited and not detonation limited. That is to say, you could advance the timing to the point where power drops off from excess negative work and still not detonate yet.



The more efficient the combustion chamber, the lower the amount of advance required for best power, and the more power there will be overall...