A short how a rotary works article

[pgmfituner]

The first thing you notice about rotary engines are their incredibly compact dimensions. A basic 13B (1.3 liter) engine is approximately the size of a beer keg and can be lifted by one fit person. At the same time, it has a volumetric capacity twice that of a conventional piston engine of identical rated displacement.

How is this possible13B Together?
The secret is in the rotary engineering package. Each rotor section (rotor and housing) form three working chambers, which work simultaneously to move its entire rated displacement on each turn of the eccentric shaft. How it does this will be the subject of later in the 'How Do Rotary Engine Work Section'; for now though, let's look at the components and nomenclature.

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Working ChambersCOMPONENTS AND NOMENCLATURE
Rotary engines are basically a sandwich of iron and aluminum rotor housings that contain rotors and an eccentric shaft. Typical rotary engines have two rotor sections, with rotor housings providing lateral containment of the rotors within. Additionally, there are three side housings (front, intermediate, and rear) to provide fore and aft containment. Rotor housings are typically aluminum, while side housings and rotors are cast iron with machined surfaces.

The eccentric shaft connects the two rotors, 180 degrees out of phase, slightly offset from the center of rotation, and transmits power to the flywheel, similar to the crank in a piston engine. Intake ports are typically run through the side housings, in what is called a side port intake configuration, while the exhaust ports are traditionally run directly through the rotor housings, which is referred to as a peripheral port exhaust configuration. With respect to ports, one important difference between rotaries and their piston counterparts is the lack of any complicated valvetrain to control the intake and exhausts ports. Instead, the ports are opened and closed by the movement of the working chambers.

you can find more about it here

http://www.rotaryengineillustrated.com/how-a-wankel-rotary-engine-works/anatomy-summary-2.html

[talntid]

Also visit www.howstuffworks.com

[rrussell]

At the same time, it has a volumetric capacity twice that of a conventional piston engine of identical rated displacement.


So for comparing purposes (based on a four cycle engine) its basically a 2.6 liter.

Lets see if anyone can answer this. Why are large injectors needed on a rotary?

[talntid]

Cause it's a fuel hog!

[pgmfituner]

well 2 rotors are about the equivalent of a 6 cyl and a stock 13b has primary injectors that are 460cc and 460cc on secondary 2 injectors on primary rail and 2 injectors on secondary rail so 4 injectors at 460cc. if you looked at a 6 cylinder and their injector size calculate the amount of fuel they use you will see it about equals out. think of it like this one rotor has 3 sides and each side gets fired so 2 rotors equal 6 combustion cycles. all three sides are getting fired on not at the same time but as one side is firing the other is on the exhaust cycle ect. so as the rotor spins it getting fired on each side. one rotor gets 3 combustion cycle per spin so X2 =6 cyl hope that makes sense.

[rrussell]

well 2 rotors are about the equivalent of a 6 cyl and a stock 13b has primary injectors that are 460cc and 460cc on secondary 2 injectors on primary rail and 2 injectors on secondary rail so 4 injectors at 460cc. if you looked at a 6 cylinder and their injector size calculate the amount of fuel they use you will see it about equals out. think of it like this one rotor has 3 sides and each side gets fired so 2 rotors equal 6 combustion cycles. all three sides are getting fired on not at the same time but as one side is firing the other is on the exhaust cycle ect. so as the rotor spins it getting fired on each side. one rotor gets 3 combustion cycle per spin so X2 =6 cyl hope that makes sense.


Food for thought.
If you take a N/A six cylinder with a displacement of 2.6 liters at 7500rpm with a bsfc number of .5 and an a/f ratio of 13.5:1 running 460cc/min injectors you would get a duty cycle of 39.6%

Now if you take a N/A 13b rotary of the same rpm, bsfc, a/f ratio, and injectors you will get a duty cycle of 60%

So why does the rotary have higher duty cycle?

I like throwing this question out there. It amazes me how many rotary guys don't understand this.

By the way I'm NOT picking on you, just making for a good discussion.;-)

[pgmfituner]

keep in mind im not an expert but i know more than the average guy. i would say that because you have to rotors spinning at the same time you have each rotor igniting 1 time per rotor at the same time. so a piston engine has a firing order where only one piston is fired at a time, so the fuel is getting burned at about half the rate of a rotary. the rotary has a firing order but each rotor having 3 sides during a cycle both rotors are having one side EACH fire. because the rotor not only rotates on the eccentric shaft it also at the same time rotates inside the housing it allows both rotors to be firing a cycle at the same time and its called planetary motion (rotation and orbit). thus requiring twice the fuel. that could be totally wrong but at least i gave it a shot. if you know the answer let me know. like i said i dont know everything about them but i know my fair share.

[rrussell]

keep in mind im not an expert but i know more than the average guy. i would say that because you have to rotors spinning at the same time you have each rotor igniting 1 time per rotor at the same time. so a piston engine has a firing order where only one piston is fired at a time, so the fuel is getting burned at about half the rate of a rotary. the rotary has a firing order but each rotor having 3 sides during a cycle both rotors are having one side EACH fire. because the rotor not only rotates on the eccentric shaft it also at the same time rotates inside the housing it allows both rotors to be firing a cycle at the same time and its called planetary motion (rotation and orbit). thus requiring twice the fuel. that could be totally wrong but at least i gave it a shot. if you know the answer let me know. like i said i dont know everything about them but i know my fair share.


Getting warmer lol

I'll let it go for the rest of the day and give the answer later tonight to see if anyone else wants a shot at it.

[sr240]

ok im confused

[pgmfituner]

the thing is is your calculations for the 6 cyl is using 6 injectors and were only using 4 at that time of rpm because the secondaries would be on.

[pgmfituner]

it has to be because you have 2 combustion cycles firing at the same time right¿ also the 6 cyl would have 6 injectors and we have four so that would alter the duty cycle. im more than happy to learn so ill wait.

[pgmfituner]

ok how about this the rotor is spinning and each side is doing a job such as intake, exhaust, ignition, so even though you are only igniting one side of the rotor per housing, you are still having to load fuel to the next side so its ready to fire when it comes to that cycle. basically you have to give enough fuel for the other combustion cycles because the rotor fires each side constantly. just another idea. LOL this is fun.

[rrussell]

For reasons of simplicity we will take a look at one rotor and one rotor housing.

One rotor housing has two injectors. We will make them each 460 cc/min.

One cycle will swept 40 cubic inches. This means you need enough injector to supply fuel four 40 cubic inches.

So now we have to look at how much time we have to open the injector before the next cycle. This is the key point, because on a rotary we only have 360 degrees of crank rotation before the next cycle. On a four cycle we have 720 degrees before the next cycle, twice the amount of time.

So we have to flow enough fuel for 40 cubic inches of volume in half the amount of time. At idle this is not a problem but as rpm increases there’s less time for injectors to be open and duty cycle goes up.

On a 2.6L four cycle six-cylinder engine there is 26 cubic inches per cylinder. You have a lower amount of volume with twice the amount of time to add fuel.


On a six-cylinder engine at 7500rpm you have 16 m/s of time to work with.
On a rotary engine at 7500rpm you have 8 m/s of time to work with.


This is why rotary engines have stage injection, so they can have a good idle and lower rpm throttle response while running only the primary’s injector’s and then bring in the secondary injectors as fuel is needed at a higher rpm.

[pgmfituner]

"So now we have to look at how much time we have to open the injector before the next cycle. This is the key point, because on a rotary we only have 360 degrees of crank rotation before the next cycle. On a four cycle we have 720 degrees before the next cycle, twice the amount of time." so i was close to the right answer?

[rrussell]

Yep you were on target;-)

[pgmfituner]

cool so im not as stupid as i thought lol. rotary has always fascinated me and i have done a lot of reading and helping my buddies with theirs and i just finally got mine so mow i get to get some more experience under my belt. do you own a rotary car because you seem to know your sh#t. not many people seem to know how they work. they are very simple when you get the basic idea. i think they just scare people because not a lot of people see them or get to see the insides of one. i admit when i seen the inside of my first one it was intimidating until i realized that its fairly simple. thanks for the brain teaser that was fun.

[pgmfituner]

any tips or info you have available please post i should have quite a few more rotary lovers here posting soon. i have been letting everyone know that we have a rotary section here now.

[rrussell]

cool so im not as stupid as i thought lol. rotary has always fascinated me and i have done a lot of reading and helping my buddies with theirs and i just finally got mine so mow i get to get some more experience under my belt. do you own a rotary car because you seem to know your sh#t. not many people seem to know how they work. they are very simple when you get the basic idea. i think they just scare people because not a lot of people see them or get to see the insides of one. i admit when i seen the inside of my first one it was intimidating until i realized that its fairly simple. thanks for the brain teaser that was fun.


I had a 87 turbo II. It was a lot of fun but I wanted a DSM really bad and sold it.

I did a lot of reading about them and still have a rotor, shaft and housing sitting in my computer room just for studying. I was going to build the piss out of one but found out its not that cheap.:-(

Their a cool engine but they do have their weak points.

[k-man]

i have far too many rotary powered things. i think i need help or somthing.

[Turbo_Z]

i have far too many rotary powered things. i think i need help or somthing.


I can help you by taking a rx7 chassis off your hands. Plus, it wont be rotary powered. Just a nice environmentally challenged turbo small block. seriously. :D

[pgmfituner]

lol

[k-man]

i have far too many rotary powered things. i think i need help or somthing.


I can help you by taking a rx7 chassis off your hands. Plus, it wont be rotary**powered. Just a nice environmentally challenged turbo small block. seriously. :D



its already a environmentally challenged turbo rotary!