Do rotaries get detonation??

[liner33]

Thinking about buying a RX-8 coming from a tuned Skyline i'm pretty focussed on det but i notice the RX will happily run on 95, since the wankel engine is clearly witchcraft;) its not something i have much experience of but thinking how they work and therefore squirting oil into the chamber and low octane fuel you would think that would be a recipe for det but does detonation become a problem on the wankel in general??

[sherman]

If you understand this I think it should explain what your after.

In an engine of the type wherein the combustion of fuel is initiated by a detonation wave, a plurality of axisymmetrical rotor elements are fixed along the length of a drive shaft. The drive shaft has a central longitudinal chamber which is supplied with the fuel mixture. Each rotor element has an annular initiation chamber which communicates with the central chamber of the shaft and a system of ducts which extend outward from the initiation chamber to exhaust openings. The initiation chambers and the associated systems of ducts are selectively filled with the fuel mixture and detonation is selectively initiated in the initiation chambers. This detonation produces detonation waves which propagate outward in the ducts resulting in the combustion products being ejected from the ducts in the form of high speed jets to produce rotational moment on the rotor/shaft unit. The speed of the exhaust jets may be modified to tailor the jet speed to the speed of rotation by varying the divergence of nozzles at the ends of the ducts or by injecting a secondary fluid into the exhaust jet.

[otolith]

They don't need high octane fuel because they run a fairly low compression ratio and are naturally aspirated. If you turbocharged it and turned the boost up to 11 you'd need to worry.

I'm intrigued that you expect it to be an issue, it's not something that most people with most cars have to worry about.

[liner33]

I wont be leaving it standard i'm looking at turbocharging and the car will certainly have nitrous fitted pretty much immediately

[od404]

Any engine where you are pushing in cylinder temperatures and pressures can suffer from detonation. While the rotary engine does have a low compression by nature of its internal geometry, it also runs very hot compared to most piston engines. This is where the problem will lie.

In stock form the engines in both the rx-7 and rx-8 will have been designed not to suffer detonation, but if you start tuning you want to make sure you don't get ANY detonation as the apex seals do not stand up to the forces created by detonation. Even mild detonation that a piston engine might survive will kill a rotary (I found that out the hard way).

So given that you are tuning the car, I would make sure that you keep a close eye on intake temps and your AFR's to make sure you steer clear of any det. Good luck with the work!!

[liner33]

Many thnaks , what kind of temperature range for the egt's same as a piston engine or lower??

[od404]

In general, you'd be looking at higher egt's on a rotary

[papercup]

od404 said:

In general, you'd be looking at higher egt's on a rotary

...and its high EGTs that will kill your RX-8 engine far quicker than the RX-7. That was the trade-off that Mazda took. The 7 engine had the exhaust port in the swept area of the tips and handles high EGTs much better. The 8 engine moved them to the side to make it more reliable over time but when you add forced induction the high EGTs will kill the side seals much faster.

Andy

[Vixpy1]

There is a simple rule on Rotarys, You really do not want any Det.. ever!