kartweb

Rotary combustion chambers present some detonation challenges that won't be found in a piston motor. Detonation is one of the reasons the motor can't be tuned to run as efficiently as an up-n-downer which can be seen from the higher EGT output.

I've done a lot of work on 2 strokes and some years back with turbo 4 strokes, both using nikasil cylinders. Learned a lot of nifty science on things like Infra Red and the impacts it has on spontaneous ignition.

I wonder; has anyone done any real research on detonation and rotaries that they would be willing to share?

MazdaManiac

iTrader: (3)

The higher EGTs have nothing to do with the motor's detonation resistance. At least, not directly.
It is only the overall thermal efficiency of the motor (BSFC) that leads to higher EGTs.
Though, much of the residual heat is the product of more combustion cycles per rev on each exhaust port.


Yes.

dannobre

iTrader: (3)

This should get interesting

StealthTL

iTrader: (1)

Nah, Maniac had to go back over a month to dig that one up, he's just setting out "bait"......

S

MazdaManiac

iTrader: (3)

Why would I do that?

I was just doing a search under "detonation" and this came up.
I figured I would correct it before I moved on.

I'm eagerly awaiting part 2.

StealthTL

iTrader: (1)

I like the new avatar...


S

faboo

+1

j9fd3s

detonation and preignition are different and due to the physical layout of the rotary engine, happen in different places.

some of the causes are the same, intake air too hot, rotor face temps too hot, housing temps too hot.

gasoline self ignites at a fairly low temp....

MazdaManiac

iTrader: (3)

The autoignition temp of gasoline is fairly consistent, regardless of pressure and vapor density, which is frustrating.
However, the OP seems to be more interested in detonation than preignition, so we should constrain the discussion to flame front speed related information.
Since the OP has so much experience with flame front propagation in his previous life (during the Carter administration), I'm sure he will have some anecdotes from his youth that will enlighten us all.

zoom44

im sorry i need a bit of clarification, please. In the sentence i have quoted are you stating:

a. "in the rotary engine pre-ignition and detonation happen in different locations within the combustion chamber"

or

b. "with the rotary engine pre-ignition and detonation happen at different locations from each other during the combustion cycle"

or

c. "in a rotary engine pre-iginition and detonation occur at different locations than they occur in piston engines"

MazdaManiac

iTrader: (3)

I think j9fd3s meant in different physical locations within the combustion chamber, though it would be somewhat correct if he meant in different timing allocations within the combustion cycle.
There are, technically, to completely different windows for pre-ignition in the combustion cycle, one being far more damaging than the other.
There are also two distinct "zones" of detonation in the Renesis because of the shape of the pockets on the rotor faces.

zoom44

hence why i asked the questions jeff- i wanted to know what HE was saying location or timing. or whether he knew there was a difference

olddragger

iTrader: (3)

cant pre ignition occur anywhere there is a hot spot? It is not really dependant on location. by design an engine can be more prone in certain areas.
The rotary really doesnt have any quench(if i have that word right) affect does it?
olddragger

MazdaManiac

iTrader: (3)

Hot spots aren't the only cause for pre-ignition - in fact, the rotary motor has far fewer places to form hot-spots.
Pre-ignition is typically caused by localized changes in charge density, the result of uneven mixing of air and fuel and sudden changes in pressure from the movement of the compressed charge through the combustion chamber.