explain rotary motors to me

[Flieger]

Originally Posted by island911

Spot on. The number of Crank rotations do not apply. (lots of cranky posts here)

It's a 4-wobble engine.

fwiw, the Wankel has positive displacement cycles - 4 of them- where as a 2-stroke has two. ...relying largely on air flow properties (harmonics) for scavenging.

OK, I was looking more at shaft revolutions and power "strokes" per triangle side. Maybe that is where we are seeing things differently. Shaft revolution vs. wobble.

Anyway, lets just agree to disagree. The engine has some properties of both 2 and 4 stroke piston engines but is so different as to make comparison useless.

[winders]

Originally Posted by Flieger

Anyway, lets just agree to disagree. The engine has some properties of both 2 and 4 stroke piston engines but is so different as to make comparison useless.

Max,

What makes a two-stroke cycle piston engine a two-stroke cycle piston engine is the two component cycle. The Wankel cycle and two-stroke cycle piston engine are very different in regards to their cycles.

The RX-7 engine is no way like a two-stroke piston engine. At least the Otto cycle of the typical four stroke engine and the Wankel cycle of the Mazda Rotary have the same four components.

Scott

[rattlsnak]

ok, so if i have fuel, spark and compression, why doesnt it start????????

[wwest]

Originally Posted by rattlsnak

ok, so if i have fuel, spark and compression, why doesnt it start????????

How is the spark timed in relation to the lobe/rotor rotational position...?

If the timing is somehow "taken" from the mainshaft then rotor position in relation to the mainshaft will be very critical. Ignition will fire for every 360 degree rotation of the mainshaft.

[masraum]

Originally Posted by rattlsnak

ok, so if i have fuel, spark and compression, why doesnt it start????????

Sounds like you're fresh out of witchcraft.

When he put the wankle together did he do it in a pentagram with 5 black candles at each point?

You would probably have better luck over at Miata.net than here. I know that Miatas don't have rotaries, but there are lots of rotary fans there. I'm sure there may be a Rotary/RX-7 forum too, just not sure if it would be full of idiot ricers or knowledgeable helpful folks or not.

[rattlsnak]

Originally Posted by wwest

How is the spark timed in relation to the lobe/rotor rotational position...?

If the timing is somehow "taken" from the mainshaft then rotor position in relation to the mainshaft will be very critical. Ignition will fire for every 360 degree rotation of the mainshaft.

Thats what ive been trying to figure out, but after research, there is only one way for the rotor to be installed on the E-shaft, so there really is no 'timing' of any sort. The spark plugs fire every rotation of the e shaft, as one of the three rotors is always on the power stroke as they turn 1/3 the speed of the eshaft, but there is a crank angle sensor im trying to research.

[Adam993]

Originally Posted by rattlsnak

Thats what Ive been trying to figure out, but after research, there is only one way for the rotor to be installed on the E-shaft, so there really is no 'timing' of any sort. The spark plugs fire every rotation of the e shaft, as one of the three rotors is always on the power stroke as they turn 1/3 the speed of the eshaft, but there is a crank angle sensor im trying to research.

OK so I'm not going to get involved in the arguing above but what i will say is that freshly rebuilt rotary engines are renowned for not starting off the key.
Having rebuilt many!!!!!! my suggestion is to make sure you have the timing set up correctly (markings on the distributer/crank angle sensor at the end with the cog drIve, you will need to read the shop manual and/or google) Once you are sure of your work the car with compression, spark, fuel and correct timing will more then likely need to be tow started! (yes, painful I know!) once you manage to start the car let it run for about half an hour to let everything bed in correctly and you should be able to start it off the key from then on.
Now, what I am interested in is how you managed to do a compression test on the engine as it is not done in the same manner as a piston engine......., not that I'm doubting your ability but you may find you don't have the compression that you think you do.......(Google will help with this too!!)
Good luck! and let me know how you go.

[island911]

Originally Posted by Flieger

..
Anyway, lets just agree to disagree. ...

I don't get it. What part of my post do you disagree with?

Originally Posted by winders

Max,

What makes a two-stroke cycle piston engine a two-stroke cycle piston engine is the two component cycle. The Wankel cycle and two-stroke cycle piston engine are very different in regards to their cycles.

The RX-7 engine is no way like a two-stroke piston engine. At least the Otto cycle of the typical four stroke engine and the Wankel cycle of the Mazda Rotary have the same four components.

Scott

That's not right either. Don't conflate cycles and stroke. I mean even a jet engine can be broken down to 4 thermodynamic cycles - intake/compression/ignition/exhaust.


. . . should we count the crank rev's?

meh - I suppose that we should all just agree to be disagreeable.

[winders]

Originally Posted by island911

That's not right either. Don't conflate cycles and stroke. I mean even a jet engine can be broken down to 4 thermodynamic cycles - intake/compression/ignition/exhaust.

I am not conflating cycles and stroke. You are the one making a mistake here. A jet engine has one cycle (Brayton), just like an Otto, Wankel, or Two-stroke cycle engine. Not four...

Yes, a turbofan engine has the same four components in its Brayton cycle as does an Otto cycle piston engine. But, in a turbofan engine, the combustion takes place at constant pressure, rather than with the Otto cycle and Wankel cycle, which are constant volume.

The difference here is that the two-stroke piston engine uses the two-stroke cycle which is a two component cycle.

A Wankel cycle engine is not a two stroke engine or anything like a two-stroke engine and is more akin to an Otto cycle engine because it has the same four components in its cycle as the Otto cycle engine.

Scott

[rattlsnak]

Originally Posted by Adam993

OK so I'm not going to get involved in the arguing above but what i will say is that freshly rebuilt rotary engines are renowned for not starting off the key.
Having rebuilt many!!!!!! my suggestion is to make sure you have the timing set up correctly (markings on the distributer/crank angle sensor at the end with the cog drIve, you will need to read the shop manual and/or google) Once you are sure of your work the car with compression, spark, fuel and correct timing will more then likely need to be tow started! (yes, painful I know!) once you manage to start the car let it run for about half an hour to let everything bed in correctly and you should be able to start it off the key from then on.
Now, what I am interested in is how you managed to do a compression test on the engine as it is not done in the same manner as a piston engine......., not that I'm doubting your ability but you may find you don't have the compression that you think you do.......(Google will help with this too!!)
Good luck! and let me know how you go.

This is a friend of mine and were doing it over the phone. It is an aviation engine and is on an engine stand, not in a car. I have not seen it in person yet, but plan to this weekend. I'm just going by what he has told me. I bring up the timing issue earlier, as that is the one issue I'm not sure he has right. I have tried google and really cant find the correct answer. I know there is a mark on the crank angle sensor that lines up with the split in the housing. BUT, it says to line up the yellow mark on the crank pulley, but how do you know which rotor is at TDC? Anyway, I'm doing some research on how to find TDC #1 and then time it correctly and will see what happenes at that point.

[hcoles]

this may be OT but I was reading re. Otto cycle engines because of this thread and investigated the Atkinson cycle engine because I have one now in a Lexus ct200 (wife car). Turns out the Atkinson cycle engine is becoming somewhat common in hybrids. The Atkinson cycle engine is ~10% more efficient at the expense of hp/cid, this is made up with battery power when needed.

[winders]

Originally Posted by rattlsnak

It is an aviation engine...

Is your friend crazy? This process should be done or, at the very least, overseen by someone who knows what they are doing. This engine is a not toy for Christmas morning....

scott

[rattlsnak]

As long as it quits over an empty field where nobody gets hurt, it's all good..

[Flieger]

OK, who cares how many "cycles" the engine has?

The facts are it has intake, compression, power, and exhaust areas, and that it has one power "stroke" per lobe per shaft revolution.

[wwest]

Wankel Rotary w/base/Atkinson/Miller cycle modes.

Wankel Rotary ~18:1 base/native compression ratio, DFI plus intercooled SuperCharging, linearly modulateable SC. Triple intake ports with the second and third displaced rotationally and having electromagnetically controlled valve close/open capability. Rotational displacement of the 2nd intake port/valve provides for CR of ~15:1, 3rd valve opening limits CR to <10:1.



"Otto" mode, idle and/or simple cruise, no boost and the axillary inlet ports are closed, ~18:1 compression ratio.



Moderate acceleration, engine load, loading and the 2nd intake valve opens resulting in ~12:1 effective CR, no boost, Atkinson cycle.



HARD acceleration, HIGH engine loads/loading, 2nd & 3rd intake ports now open, engine's "base" compression ratio <10:1, Miller cycle.

"Measured"/Metered boost as a function of gas pedal position beyond 50%. Engine "base" effective CR now <10:1, SC boost raises effective CR in a linear fashion.



Positive displacement variable speed SC. SC is driven via a PSD(CVT) summing machine, engine drive as one input, synchronous multiphase AC motor as the second input. Variable frequency inverter drive allows linear control of boost level in depended of engine RPM.



SC "meters" intake airflow, NO throttle plate.

[island911]

Originally Posted by winders

I am not conflating cycles and stroke. You are the one making a mistake here. ...

Scott

Yeah, I was speaking loosely there, hoping that flieger would split that "process/cycle" hair. ...he needs something to save a bit of face on this one. -he still squirms.

Anyway, you don't need to tell me that a Wankle is not a 2-stroke engine.

Oh, and glad to see you finally get this all straight. Happy new year.

[wwest]

4-cycle/stroke engine has ONE power event for each 720 degrees of power producing mechaniism rotation.

2-cycle/stroke engine has ONE power event for each 360 degrees of power producing mechanism rotation.

Wankel has ONE power event for each 120 degrees of power producing mechanism rotation.

Wankel = 0.6666-cycle/stroke...???

[Flieger]

Well, I was going to say something about compression (or power) being a process, and the whole suck squeeze bang blow thing being a cycle but I just don't care anymore.

[lindy 911]

The OP wanted to know how a rotary engine worked and Quicksilvers animated post shows with great efficiency how it does. It cannot be compared to a piston engine just like it can't be compared to a turbine. It makes power in a different way than either one. They all have a form of intake, compression, ignition and exhaust but they all do them very differently. It's not a two stroke, four stroke or even .666 stroke; it's a rotary.

[tadd]

A bit different way to think of the rotary is to remember the 'combustion volume' smoothly sweeps all the way around the face of the ellipse... So it's really close to a turbine, just viewed at 90 degrees.

In other words, in a turbine the combustion process is axial to the output rotation. The rotary has the same smooth 'blending' of the combustion events, just radial to the rotation.

Rotarys are inefficient due to the large surface area of the 'combustion chamber'. Thermal coatings help. Mazda has played with ceramic inserts for years. Amusing though is that all the surface area actually makes the rotary really nice to use with hydrogen as a fuel. I'd like to think that's mazdas endgame for keeping the design 'alive'.

t