rotarygod

iTrader: (1)

First of all you may just want to print this as it is really freakin long!!!

This article is primarily intended to educate people on what makes the rotary engine so different and unique and why it can not be compared accurately in size to a piston engine.

The rotary engine is a 6 stroke internal combustion engine. I know, people will probably start screaming at me for this so lets get into a little explanation as to why and how typical mathematical formulas for piston engines don't work.

First of all, lets get the terms "stroke" and "cycle" defined (Some of you get your heads out of the gutter!) since everyone commonly gets these terms interchanged. They are not the same thing. Every internal combustion engine whether it is a 2 stroke, 4 stroke, diesel, gasolines, propane injected, etc. is a 4 cycle engine. Why? All of these engines take in air (intake), compress the air (compression), ignite the air whether by spark plug or glow plug (ignition), and expell it out the tailpipe (exhaust). There you go 4 cycles. Simple isn't it. The term "stroke" in this context refers to how many times the crankshaft or eccentric shaft makes a piston go up or down to complete the cycle.

The connecting rods and pistons are just an extension of the offset lobes of the crankshaft. This is also true in regards to a rotor and eccentric shaft. When the lobe rotates upward, the piston goes up. When the lobe rotates down, the piston goes down. Every time it moves one way is considered a stroke. In a 2 stroke engine, all 4 phases or cycles of the combustion process are completed in only 2 strokes of the piston, 1 up and 1 down. This is only 1 complete revolution of the crankshaft. In a 4 stroke engine, it takes 4 strokes of the piston, up, down, up, down to go through the complete combustion process. This is 2 complete revolutions of the crankshaft. It's all a very simple mathematical relationship.

Now lets go look at the workings of a rotary engine. If we look at a rotary engine eccentric shaft and compare it to a piston engine crankshaft, we see essentially the same piece. Both have lobes and because of this both engines will have a stroke length, even the rotating rotary. It doesn't matter if it is a piston going back and forth or a rotor going round and round. The crankshaft motion remains the same. On a rotary engine, the rotors are spinning at exactly 1/3 the speed of the eccentric shaft. From the time that the air entering one chamber goes through the combustion phases to the time it leaves the engine from the same chamber (rotor face), the eccentric shaft has gone around 3 complete times unlike a 4 strokes 2 times or a 2 strokes 1 time. If we do the math we see that the lobes of the eccentric shaft must have gone up and down 6 times (up, down, up, down, up, down). Since it does this process the exact same way every time for every rotor face, it is a 6 stroke engine. Thats right the rotary engine is a 6 stroke! Do not confuse these strokes with the 4 internal cycles that every engine has!

Let's sum this up in a simple chart to visually explain how this works.

2 stroke engine (up,down) - 1 complete crankshaft revolution

4 stroke engine (up, down, up, down) - 2 complete crankshaft revolutions.

6 stroke (rotary) engine (up, down, up, down, up, down) - 3 complete crankshaft (eccentric shaft) revolutions.

See a pattern? All of these engines though are still 4 cycle engines! They are different stroke engines though so the amount of work they do per time is very different. A 2 stroke engine does twice the work per amount of time that a 4 stroke does. Don't believe me? Go race 2-80cc motorcycles, 1-2 stroke and 1-4 stroke and see who wins! This must mean that the rotary engine does the least amount of work per time than both other engine types. Yes it does. But, unlike a piston engine, it uses 3 sides of it's piston (rotor) at a time. In reality it makes no difference if we have 1 rotor with 3 usable faces or 6 rotors with 1 usable face each as in a piston engine.

Here's a little info on how to properly figure out displacement on a rotary engine. Everyone argues that it is really a 1.3 liter while others argue that it is really a 2.6 liter engine. They are both wrong! If we look at how a piston engines volume is calculated we arrive at a displacement based on total swept volume of every piston added together. It is not based on rpm. On a rotary, displacement is figured using one rotor face in one complete revolution then multiplyed by 2. This only leaves the total for 2 combustion chambers though and the rotary has 6! Since the volume of a 13b rotary is rated at 1.3 liters (only 2 combustion chambers) it really adds up to 3.9 liters!!! I can hear it now, "...but we only have 2 rotors!" So what. Like I said it makes no difference if there are 2 rotors with 6 faces or 6 rotors with one face each. the total is always 6 and the base numbers are only based on 2 chambers. The rotary merely does 3 times the work in a package 1/3 the size. It's just a 3.9 liter engine crammed into a 1.3 liter body. Just so none of you start a fight over this, I have a second write-up that explains this so don't chastise me yet!!!

In case anyone is curious I did some math to determine what the 13B rotary would be sized at if it were a piston engine. The results are pretty neat. First of all the rotary would be a 3.9 liter, 6 cylinder engine. It would be a 6 stroke. Each cylinder would be 6.54" across (damn big piston!) but the stroke length would only be 1.18" in length peak to peak. Not much there. Interesting isn't it. Now just imagine a way to make all this work with only 2 intake runners!

In all fairness to the terms in this article, the word "stroke" can be interchanged with the word "cycle" since both technically have the same definition. The terms "periods", "quarters", or "phases" can also be used correctly. I merely wrote it the way I did to get a certain mental picture going.

Before you guys give me flak over this go read part 2 below.

rotarygod

iTrader: (1)

In the first section I dealt with why the rotary engine is really a 6 stroke engine and why displacement is really 3.9 liters and not 1.3 liters. This article will explain why the rotary engine doesn't have the torque or horsepower of a good 3.9 liter engine or why it doesn't get the gas mileage of a 1.3 liter engine. The world has always wondered so here's why.

Remember in the first article I stated that the true displacement of the rotary engine, if figured out according to the way piston engine volumes are calculated, is according to the total number of rotor faces and not the number of rotors, nor does it have anything to do with rpm. This added up to 3.9 liters for a 2 rotor 13B engine and not the published spec of 1.3 liters. They just crammed all 3.9 liters into a 1.3 liter body. If the engine is really a 3.9 liter engine then why doesn't it have the low end torque of a 3.9 liter engine? This has a very simple answer. Lack of leverage. OK, what the hell does that mean?

First of all we must figure out what a lever is. It is a device that multiplies mechanical advantage over an object to do the same amount of work with a smaller amout of effort. Another way to look at it is to do a greater amount of work with the same amount of effort. It's the same thing. Let's look at leverage differences as an example in a piston engine.

What happens to a piston engine when we make it a "stroker"? Ignoring a host of other variables, it gains torque. It also gains horsepower but they are both a fixed mathematical ratio between each other and you can't increase or decrease one without the other. Why did it gain torque? Greater mechanical advantage or leverage over the crankshaft. The reason being is that on a stroker crankshaft as opposed to the stock crankshaft, the lobe centerline is farther out from the rotational centerline of the crankshaft. This increases the leverage that the piston has over the crankshaft. Don't believe me? Try this. Get a short pole and hold it at the end straight out away from your body. Attach a 10 lb weight to it exactly 1 foot away from your hands. The weight is exerting exactly 10 ft. lbs. of torque on your hands. Now move that weight out away from you to 2 feet away from your hands. Now the same weight is exerting 20 ft. lbs. of torque on your hands. You have just in essence made a "stroker" (gutter heads!). Now let's get back to the engine.

Now we know that the greater the stroke length, the greater the engine torque. As I stated in the first article, the rotary engine only has an effective stroke length of 1.18". My weedeater has that! There is not very much mechanical advantage over the eccentric shaft. This still doesn't explain everything though.

Remember, in the first article I stated that if the 13B rotary were a piston engine it would have pistons 6.54" across. Now we just discovered another enemy of efficiency, flame front speed. When the spark plug ignites the mixture in the engine, it doesn't just ignite everything all at once. The spark ignites at the plug and then has to travel outward away from the plug at a certain rate of speed. While this only takes milliseconds, this amount of time gets more critical the higher the rpm gets due to the shorter amount of available time. The result is that as rpm's rise efficiency decreases. The larger the area of the piston, the farther the flame front has to travel and the greater the chance that all of the mixture does not get ignited when it should. Just can't go far enough fast enough. Todays rotaries have 2 sparkplugs per chamber to help combat this problem. Varying their ignition time in relation to each other even helps somewhat with power and emission. That's right they don't necessarily fire together even though they are in the same chamber. This can get complex so I will not deal with it at this time. Some race engines even have 3 plugs per chamber to improve efficiency and ignition wave front speed. On piston engines, Mercedes has capitalized on this and uses 2 plugs per cylinder in some of their higher end cars. Do they know something others don't?

There is also one more aspect that affects it. Remember that the rotary is a 6 stroke engine. A 2 stroke engine does twice the amount of work per amount of time that a 4 stroke engine does. A 4 stroke engine does 50% more work per amount of time that a 6 stroke does. The rotary engine does less work per eccentric shaft rotation than your typical 4 stroke counterpart. All of these characteristics combine to make an engine that has relatively little low end power and needs to be revved up to be truly powerful.

I make it sound like we should have less torque than a 1.3 liter engine due to the above reasons. This isn't true though. Remember that we still have a 3.9 liter engine even though it only uses 2 lobes on the eccentric shaft. We should not expect to develop the torque numbers of a 1.3 liter engine. It should settle in somewhere around 50% less than a 3.9 liter engine which would put it around equal to a 2.6 liter engine in power.

These traits of the rotary engine are also why the engine gets worse gas mileage than your typical 1.3 liter engine. Hell it gets worse gas mileage than your typical 2.6 liter engine. Another aspect that affects this is port timing and duration. If we had a piston engine of 2.6 liters in size that had the same intake and exhaust timing as the rotary then it would get comparable gas mileage to the rotary. The 12A/13B rotary though have much more exhaust duration than intake duration due to the peripheral exhaust port location. This contributes to several factors which decrease efficiency. Exhaust gas dilution is one of them. For each stroke there is a small amount of overlap. The exhaust ports and intake ports are open to the same chamber at the same time for a short amount of time as measured in degrees of eccentric shaft rotation. The higher the rpm's the less important this becomes since air velocity will generally keep the gasses where we want them to go. At lower rpm's though the intake and exhaust air velocity is not very high. This will cause some exhaust to go back through the combustion chamber again. When this happens volumetric efficiency decreases and there is less room for fresh air to fit inside the combustion space. Also this recirculated exhaust gas is very hot. A hotter air molecule is larger than a cold one which means a fewer number of molecules can fit in the same area per amount of pressure exerted on them. Another aspect of the rotary's peripheral exhaust port configuration that contributes to less low end power and greater fuel consumption is its incredibly long duration or time it is open for. Unfortunately when we make the port bigger we also change it's timing. We don't have the luxury of being able to mill out a head to accept a larger valve while still being able to use the same cam. The timing is really only optimized for high rpm use. We are leaving it open for too long which gets back to the whole overlap problem. Again, all of this is just a generalization and can be affected by how well the intake and exhaust flow and how well they can scavenge. The affects of scavenging, intake design, helmholtz effect, and proper exhaust design are all out of the scope of this article. So just assume it is an even world.

Luckily there is a cure for this. It is called Renesis! It is the new 13B based rotary engine in the new Mazda RX-8. The exhaust ports are no longer in the periphery of the chamber but have rather been moved to the side housings. This allowed the designers to more appropriately optimize the port timing duration. The location also allows more port area leaving the engine. So now we have more area to flow air out of faster. This new location also completely got rid of the port overlap. There is actually 64 degrees of dwell. This amount of dwell was originally greater in the early test engine called the MSP-RE since it had the intake timing of the '84-'91 n/a RX-7's 6 port engine. However dwell is only useful if you just have enough to get the job done but not so much that you are getting losses from it. Because of this Mazda engineers learned that they could open the intake earlier than previously and still maintain all of the other good aspects of the new exhaust layout. A bigger intake port = more time for air to enter and a greater cfm rating through the port. Less turbulence through the port as well. Less overlap gives us less dilution of the intake air and a cooler intake charge. More available room for incoming air. Volumetric efficiency increases. Since efficiency goes up, our use of gas gets more efficient. In other words it takes less fuel to do the same amount of work. The result, better gas mileage. With todays gas prices this is a very welcome thing. The efficiency increase also means that emissions characteristics are also improved. Another bonus with todays laws concerning air quality.

So after reading this you are probably wondering why in the world anyone would want to use one of these engines. First, and most obvious is size. They crammed a 3.9 liter engine, or more appropriately a 2.6 usable liter engine into a 1.3 liter body. Second, it is just such a simple design. There are only 3 moving parts. Fewer moving parts have less frictional losses. Also fewer moving parts have less chance statistically of failure. The more it moves, the more chances you have for failure. Third, nothing moves back and forth. So what? A piston stopping and changing direction exerts alot of stress on everything from the crankshaft to the connecting rods, to the pistons, to the wristpins, etc. Lets not also forget the stresses on the valves for being slammed open and shut as well as the temperature extremes they see during the combustion cycle. A body in motion tends to stay in motion. It is a very unnatural act to change direction suddenly or at all for that matter. A rotary just spins away in the same direction. Yes the lobes of the eccentric shaft do see stress but remember that we don't have very much leverage over them. The rotors are also exerting some of their rotational stress on the stationary gears as well so some stress is never transmitted to the eccentric shaft from the rotors. The lack of stroke length and pure rotational motional do make it very naturally adapted to high rpm use. If we look at really high horsepower piston race engines, their stroke length has been shortened to reduce the stresses to all of the engine components at high rpms. The last and most important reason why the rotary engine is still a popular engine despite it's shortcomings is because it is different. There is always something to be said for individuality and uniqueness. If you own a piston engine it doesn't matter how big it is or if it is made by Chevrolet or Honda. It is still the same device.

Just to shoot down right now any arguments on displacement think about this.

The 13B rotary engine is a 1.3 liter. Yes.
The 13B rotary engine is a 2.6 liter. Yes.
The 13B rotary engine is a 3.9 liter. Yes.

Notice that all of these statements are TRUE!!! That's right there is a truth to all of those statements. Go read both of my articles. To understand why this is so, lets define truth. Truth can be defined in a couple of ways: Anything that is not false (none of those statements is) or it can be defined as: One's individual interpretation of presented facts. This herein is the source of our debate. We can't change the facts no matter how hard we try. Arguing won't do it. What is debatable however, is each individual's interpretation of facts. If your interpretation doesn't match someone else's, you argue about it.

Here are the facts: The rotary engine as rated by Mazda is 1.3 liters because each individual rotor, following one face of one rotor through the complete cycle, has a swept displacement of 654cc or .65 liters. Multiply this times 2 rotors to achieve 1.3. Since this only accounts for 2 of the total of 6 rotor faces, we multiply our answer by 3 to get an actual displacement of 3.9 liters. However since the rotary engine is a 6 stroke engine and not a 4 stroke engine since it takes 3 complete eccentric shaft revolutions to fire all faces instead of the typical engine's 2, it only does 66% the work of a 4 stroke 3.9 liter engine. Calculating for this we divide 3.9 by 1.5 to get a total of 2.6 liters equivalent work to a 4 stroke piston engine. All of this from a 1.3 liter in physical size package.

No one can argue that this is not correct and any response saying otherwise will have been explained by what I just said. Any debate will only focus on one aspect and not the total facts.

Just to put a cap on this whole thing: If at any time you try to calculate proper sizing for a turbo, intake manifold runners, intake plenum size, exhaust size, etc, and you try to use the 1.3 liter number in your equations, you will be way, way, way off!!!!!!!!! There are only 2 ways to flow more air: increase displacement or increase rpm. A 1.6 liter Honda engine doesn't flow anywhere even remotely near what a 13B (1.3 liter) flows per the same rpm. Just some food for thought.

Rebut that! I need the entertainment! Hehe!

See if you can guess which number I think the engine REALLY is. I'm not telling! It is one of the above numbers but which one? If you ask me though I will agree with them.

Now you guys can tear it all apart!

honegod

I'll nibble.
I think it is a two stroke, with the "piston" attached to the crank with a multiplication gear.

such that as the 'piston' does its cycle it spins the crank 3 times.
this would also explain the low torque, the 'piston has 1/3 the leverage on the crank because of the 'gearing'.


pretty feeble, I know, but this is all I came up with in a hurry to justify the well deserved Bump this superb post of yours rates.

peejay

A rotary is a four cycle engine.

A "cycle" is when a working chamber goes from minimum to maximum size or vice-versa.

In piston engine terms, a piston goes from top dead center to bottom dead center, or vice-versa. Since this is motion along a line in one direction, people interchange the word "cycle" with "stroke". This works OK for piston engines although "cycle" is technically correct. Piston goes down stroke for intake cycle, up stroke for compression cycle, down stroke with combustion cycle, and up stroke for intake cycle.

In rotary engine terms, it is when a rotor face goes from horizontal to vertical, or vice versa. Do not get confused by the fact that there are three working chambers per rotor, they are all separate entities and each chamber has four distinct cycles of intake, compression, combustion, and exhaust .


That's all I am going to touch on.

KevinK2

Lots of good, correct thought with 1 major flaw.

The false assumption (not fact) here is that what is known as a linear stroke for a boinger, ie 180 degrees of crankpin rotation and related piston translation, has anything to do with defining rotary engine and/or eccentric shaft functions . It doesn't.

The stroke of a rotary occurs during 270 degrees of eccentric rotation, and can loosely be considered as the increase in distance from a central point on the rotor face to a related central point on the opposed housing face, going from 'tdc' to 'btc' type positions. In fact, using the projected area of a rotor face, and the known displacement per face, the implied stroke is about 3xe, vs 2e for a boinger (relates to 270 degrees of stroke vs 180 deg for boinger)

The rotary is not a 6 stroke. it's a 4 stroke. Each of 6 rotor faces goes thru 4 non-linear strokes related to the 4 otto cycles, during 3 revolutions of the eccentric.

Using usual unofficial swept volume definitions (no SAE standard exists), it's a 3.9L with 3 revs to fire all chambers. Using Mazda's wacky definition, each rotor is a piston that fires once per rev, so it's displacement should be like a 2 stroke, 2 piston engine, each piston at .65L for a 13B, or 1.3L total.

A boinger-type closest equal, in theory, would be a 3.9L 6 cyl, with 1.2" stroke, and a .67 overdrive gear just before the 'official' output shaft of this engine. In two revs of this output shaft, this would give 2.6L active displacement of air, and 4 combustion events with 270 degree strokes, just like a rotary.

Project84

I agree with KevinK2 and peejay. How do you figure a rotary for a 6 stroke engine? If you follow one face of the rotor around (just as you would follow 1 piston up and down) you get intake, compresssion, power or combustion, then exhuast. Thats only 4, not 6. It would be madly inefficient to accomplish those 4 actions in 6 strokes don't you think?

Next you have this:
2 stroke engine (up,down) - 1 complete crankshaft revolution

4 stroke engine (up, down, up, down) - 2 complete crankshaft revolutions.

6 stroke (rotary) engine (up, down, up, down, up, down) - 3 complete crankshaft (eccentric shaft) revolutions.

I don't understand this last part about the rotary. It doesn't go up and down. But your logic is still incorrect. 6 strokes on a rotary does not equal 3 rotations of the crank. Thats overly inefficient as well. If you follow one face of the rotor around the housing for 360 degrees, or from intake stroke, all the way back around to intake stroke, you will have completed the 4 strokes, (intake, compression, power stroke, and exhaust) and have gotten 3 rotations from the crank shaft. Under your logic, your 1 face of the rotor would have to complete intake, compression, power stroke, exhuast, intake and copression (6 strokes) to get 3 rotations from the crank.

The connecting rods and pistons are just an extension of the offset lobes of the crankshaft. This is also true in regards to a rotor and eccentric shaft. When the lobe rotates upward, the piston goes up. When the lobe rotates down, the piston goes down. It looks like your whole formula is based on this theory, but again, the rotor go around, not in a linear motion, so the rotation of the lobe on the rotary engines eccentric shaft cannot be correlated to a up/down motion. Yes, the shaft lobe may point up and down at different points, but throughout its travel, it will point at each of the different apex seals at one point or another. Click here and watch the rotor going around. You can click on the red button to stop and go one stroke at a time. Watch the offset point of the lobe and notice how at different times, its in line with each of the 3 apexes.

peejay

Quote:

Using usual unofficial swept volume definitions (no SAE standard exists), it's a 3.9L with 3 revs to fire all chambers. Using Mazda's wacky definition, each rotor is a piston that fires once per rev, so it's displacement should be like a 2 stroke, 2 piston engine, each piston at .65L for a 13B, or 1.3L total.

It's not Mazda's wacky definition. It's NSU's. They defined the Wankel by how much one working chamber per rotor displaces, which is effectively "displacement per single rotation". This is half of what 4-cycle piston engines would be rated at for a similar "actual" size. NSU *knew* this, and it would a great coup. It meant that their Ro80 could make power like a 2-liter engine but fall below the 1-liter taxation bracket. (Some countries tax cars by engine displacement) So people would be comaring a "1 liter" Ro80 to a 1-liter piston engine, well of course the Ro80 would be more powerful because the engine is twice as large.

(edit: got some of the vB code messed up)

black_sunshine

RotaryGod has some really interesting points. The problem that most fail to overcome is that of reciprocating engines. Most will say that, yes, the rotary is a four-stoke engine...err. .... four-CYCLE engine. If you wanted to relate it in strokes, it would more closely represent a one-stroke than a four-stroke. The rotor-face makes one complete "stroke" from intake to exhaust. This is just an idea, and frankly I totally see the whole 6-stroke thing. I mean, based on shaft rotations, yes, the shaft makes 3 complete rotations per rotor rotation. BUT, would we call a V8 an 8-stroke ( they usually have 2 pistons doing the same stroke at a slightly-offset interval). Probably not. Adding onto fundamentals of internal combustion is futile at best; the rotary IS a 4-cycle engine.

Now, the entire "x-cycle" thing is a little hard to understand. Once you get out of the linear, non-infinite reciprocating mentallity, and begin to think in an infinite circular manner, the rotary makes much more sense. How many sides does a square have? four. How many sides does a circle have? 360? 720? How about none; it's a circle. Same applies to rotaries Vs. piston engines. Does it do all four cycles? Yes. And measuring strokes is silly; a rotary has 4 difinitive angles. TDC, BDC, SDC1/2 (side-dead center). So, literally speaking, it is a one-stoke engine that operates on four-stoke principals that utilizes two-stroke and four-stroke lubrication system(s).

Displacment can be measures many ways. The standard way is to measure the corrected volume of the rotor at bdc/2. Many ideas have been thrown about as to weather this is correct or not; technically speaking, based on a piston engine, is IS correct. But, since these engine's combustion chambers physically change geometry it makes it difficult to measure everything. I think that the standard method for measurment is best, but ALL the others have validity as well. Want the true displacment? Take the CFM flow at any rpm; divide the RPM from that #, and divide by two. Then divide by 12 (for Cubic inches). hmm...

The renesis is what the rotary SHOULD have been from the get-go. Why they didn't do this to begin with, I'll never know, but I'm glad they finally did. Go Mazda! I can see these engines lasting a veeeery long time.

The 6-cycle thing is a real though provoker. I'll stick with my 3-cycle idea (doing 3 of 4 cycles at one time). Remember, don't think piston engine; they don't have a 3:1 reduction per piston.

The Wankel preplexes many; I like to think of it the way Felix (the dead one, r.i.p) thought of it. Really simply. I disagre with the NSU's measurment of displacment system; Peejay and RotaryGod said it all.

Just my 2-cents

Matt

KevinK2

Once you can think out of the piston engine box, it is obvious the rotary has 4 distinct strokes. The two TDC positions for a rotor face are at 3 and 9 o'clock, and the two BDC postions are at 12 and 6 o'clock. It takes 3 crank revs to complete these 4 strokes. Each stroke results in the filling or exhausting the rated displaced volume of the chamber in question. Just like a 4 stoke piston engine in function. It has 4 strokes, not 6, not 1. If you were sitting on a face of a rotor, each stroke would be obvious as the housing moved away and returned .......... If a theoretical 4 cycle piston engine had a combustion chamber that changed shape in a consistent way, from tdc to bdc, would it no longer have 4 strokes? Sure it would, but the rated displacement would no longer be just bore area times stroke.

Volume is usually not measured, to figure engine displacement, it's calculated based on dimensions that are usually known or easily measured. Bore area times 2 x e gives rated displacement of a piston. For a rotor face, the formula is k x R x w x e, where k is a constant, R is radius from rotor center to apex seal contact, w is width of chamber, and e is e-shaft crank offset. The change in combustion chamber shape is accounted for in the formula. Very easy for both engine types.

peejay

Cycles, not strokes. "Strokes" is a term from the piston-engine thinking box.

rotarygod

iTrader: (1)

Regardless of the fact that there are people that disagree (I was counting on this that's why I wrote it!) I'm just happy that someone actually read that hellaciously long thread! It took forever to write. I started to confuse myself after a while anyways but it was written more along the lines of addressing the inherent problems with different arguments and that there is no accurate way to argue the rotary vs. a piston engine. I just did it in a long winded way

13b-rotary-vw

I know this is an old one,

But for anyone looking for clear definition of the rotary engine and it's class, must first understand the question that is bieng asked. If you just look at the simple fact that for every 180 degree rotation there is a power pulse thus making it equivalent to the power pulse of a typical 4 cylinder engine, you will then understand that for each power pulse you would simply add the volume per chamber which in this case is 654cc or .65 liters. The difference is that in a 4 cylinder engine the standard count is for each pistons and it's complete cycle which works perfectly with the "4 stroke (otto cycle)". So we count for 2 full revolutions of a typical 4 cylinder piston engine that equates to 4x180 degree strokes each piston having a chance to fire a power pulse and also recieve 1 of each portion of the otto-cycle. It sounds way more confusing when reading it this way but, just know that at 180 degrees a 4cyl engine fires every time.

Now, If we had an 8 cyl. engine (which normaly fires at 90 degrees of crank rotation) and had it made (changing the crank shaft) to fire at 180 degrees it would work the same as a 4cyl engine. The only difference is that you would have 2 pistons working together per power pulse. Once again the real important part is where the pulse is in relation to the crank position.

The rotary got the 1.3l because it can complete the otto-cycle in just one revolution of it's e-shaft and with each face of the rotor piston (like a conveyor belt ) waiting to complete the rest of the otto-cycle. It really does not matter if the rotary engine has a 3 point piston (triangle) 5 point or any other configuration (which there are some prototypes out there). It's all in the relationship in the shaft and pistion TDC and BDC. In this case it will always be 360 for each rotor. With two rotors each 180 degrees out of phase of each other making them complete each cycle also at 180 out of phase. So when we count the completion of each pulse we get 1.3l of one revolution.

But, if we think of the fact that there are three faces for the rotor it self (the triangle again) we tend to confuse that fact with faces of individual pistons like that of a piston engine, which is an irrelevant factor in this case. We then think that it must complete each position for each face, and that is where we end up multiplying by 3. Also this engine gets compared to 4 cyl. because of the 180 power pulse that it shares with the 4 cyl. engine and gets tied to the thought of 2 revolutions per full completion of it's cycle...this wrong in more ways than it is right. I will agree that this engine (rotary) does share the same characteristics in terms of power usage as most 4 cyl. engine of relitave size, meaning that you would have about the same gearing ratios (or atleast close) to that of similar power levels...

Think of it this way, If you were on a stair machine (the escalator type) it would not matter how many stairs there were (stairs in relation to the rotor faces 3,5,7,9 ect.) but more importanly the legs you have (I.E. power pulses). I know this is a wierd analogy but bear with me, creating power and defining it can be done in many forms. We could simply jump with both legs on each stair to achieve the same goal and it would be the equivalent power as right over left. It is the same with engine definition. Pistion engines share the same classification to be defined, which is the "stroke" so it's easy to measure all these in the same class. Rotaries are confusing because most people have classified it with thier own bias. The truth remains that it is 1.3L per revolution. When it is used for power it tends to share the same gearing ratios of typical 4 cyl. engines because that is usally where it's power range works for most automobiles, that where the 2.6L comes in to play 1.3L x 2 revolutions e-shaft/crankshaft (2 revolutions per crankshaft is used to determine 4 stroke otto-cycle completion). And if you want to know the full displacement based on the full rotational cycle of the rotary engine, you must know that it takes 3 e-shaft revolutions for 1 rotor (that triangle thingy again) revolution. So 1.3L x 3 = 3.9L

So I hope that this long venting of my brain help someone out there who might have stumbled on to this thread. Like I said, it's more about the question that is asked when it comes to defining the engine in question. It's really not that hard of a concept. People just have to realize that this engine (rotary) is as close to a jet engine as possible while maintaning a reciprocating motion. It is capable of a huge volume of air movement in it's relatively small packaging. That's what is so cool about this engine!!! The piston engine although tried and true, is not the only method for harnessing expanding gasses. The key to the future has always been about practicality, efficiency, and improvment. I believe that's what every rotary engine owner is saying by just owning one. Wow I feel like I'm giving a speech (did you hear the presidential music in the background too!)

Anyway If you have a rotary engine, just know that you own a fine piece of equipment made by very hard working intelligent people that dedicated and risked everything for what we have today...really, look up the story on it...

RotaryEvolution

iTrader: (30)

i'd compare it to a 1 stroke, 1 fire per stroke of the shaft(.5 rotations).

edit: man that sounds dirty...

Kentetsu

Very interesting stuff...




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