We may be confusing a couple of things here. The terms "two-stroke" and "four-stroke" specifically describe operation of reciprocating piston engines. We may need to speak in terms of thermodynamic cycles.

Four-stroke piston engines and Wankel rotary engines both utilize the same thermodynamic cycle (the "Otto cycle"). I've been looking through my thermo books but can't locate a definitive thermodynamic cycle for two-stroke piston engines...

Quicksilver,

Look here:

Wankel rotary engine Page 2

Scott

How is there argument an the number of "strokes?" The rotary HAS NO STROKES!!! It's not a 2 or 4-stroke, it's a rotary.

Two-cycle engines have the "intake-compression" cycle and the "power-exhaust" cycle.

Scott

It's just semantics. We really mean "two-cycle" or "four-cycle". When applied to piston engines, we also happen to get the same number of strokes as cycles.

Scott

So a rotor has one cycle, an "intake-compression-power-exhaust" cycle. It's a fluid motion.

2-stroke.... 4-stroke call it what you will but I will add this little tidbit to the 2-stoke list.

Some RX-7 guys disable the oil injection systems and premix their fuel. The factory system injects engine case oil to lube the Apex seals and due to the potential failures of these systems as well as the carbon buildup from burning engine oil, premixing 2 stroke oil in roughly a 100-1 ratio with the gas would seem to give better reliability due to less carbon buildup.

There are four distinct cycles that take place in a RX-7 engine.

Premixing oil with the fuel means nothing in this case.

Scott

Guys, as previously stated, 2-stroke and 4-stroke only apply to piston engines, and define the number of times a piston has to move (up or down) for a full combustion cycle.

If you want to compare this in similar terms to a rotary, you should really be speaking of 1 vs 2 cycle (or movement) engines: 2 strokes are 1 cycle, since they use the same cycle for compression/combustion and scavenging/intake. 4 strokes are two cycle engines since they separate the steps for compression/combustion and scavenging/intake.

By this logic, wankel engines are 2 cycle engines, since they also have separate "actions" for compression/combustion and scavenging/intake. Just don't call them 4 or 2 stroke.

Oil mixing in fuel: that has nothing to do with 2 vs 4 stroke, it's a question of mechanical logistics. There are 2 stroke engines with wet crankcases which have no need for oil mixing (the old ford orbital prototypes) and 4 stroke engines which need oil mixing (some old designs, usually).

Okay, if you want to get really technical, a typical four stroke engine has a single cycle called the "Otto cycle". The RX-7 engine has a single cycle called the "Wankel cycle".

Both "cycles" have distinct intake, compression, ignition, and exhaust components that make up the cycle.

Two-stroke piston engines have two components in their "two-stroke cycle". They are "intake-compression" and "power-exhaust".

Although completely different in design, the Wankel rotary engine has the same cycle components as an Otto cycle engine and much different than that of the the two-stroke cycle engine.

Scott

Fascinating. I'm still wondering what this has to do with 911 Technical tho :)

did you get it started yet?

"..it does all four cycles in one revolutuion..."

Isn't that the very definition of a 2 stroke/cycle engine...???

What....WHAT...??!!

The Wankel is a three "piston" engine with three firings in the (common) combustion chamber for each revolution of the "crank". An equivalent 4-stroke Otto engine needs to 720 degrees of rotation for that. If you understood the internals of the 2-stroke engine in my weedeater you would undoubtedly agree. Pick one of the Wankel's three "pistons" and follow it through 360 degrees of rotation.

All one really need do is look at the physical size, weight, of a 300HP Wankel vs an 300HP Otto engine to see just how radical the differences are. Check out Dempsey's Mazda at the upcoming 24 Hours of Daytona

lobe =/= piston

piston = piston
lobe = lobe

... What he said :)

Bingo! A wankel is quite different to a piston engine. Might as well also compare a gas turbine to a piston engine and call it a 0-stroke engine :)

Wankles are the devil's work. They're powered by triangles and witchcraft. Run away!

What do you mean by "What..??!!"? Read post #30 again. It is technically accurate.

The Wankel is not:

...a three cylinder engine with three firings in the (common) combustion chamber for each revolution of the "crank".

What you call the crankshaft, the "output shaft" or "eccentric shaft", rotates three times for each rotation of the rotor. There is one firing for each rotation of that shaft.

Scott

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.

:D

Well, actually, those triangles (wedgie combustion chambers) do actually suck for capturing the bang. (so to speak)

That is why they are an inherently flawed design/configuration. ..so yeah, Run away!