The Rotary Engine: A Complex and Fascinating Design

In this article, we will delve into the world of rotary engines, specifically focusing on their unique design and characteristics. We'll explore how they compare to traditional piston cylinder engines, and discuss the advantages and disadvantages of these innovative machines.

One of the key differences between a rotary engine and a piston cylinder engine is its power stroke cycle. A four-stroke engine has one power stroke for every two revolutions of the crankshaft, resulting in 500 power strokes per minute. In contrast, a rotary engine spinning at a thousand rpm would have five hundred power strokes per minute. This difference in power stroke frequency gives rotary engines a distinct advantage when it comes to speed and efficiency.

Now, let's take a closer look at how rotary engines work. Unlike piston cylinder engines, where pistons move up and down within the cylinders, rotary engines feature a rotor that spins in a circular motion. The rotor is driven by an eccentric shaft, which creates the rotary motion. As the rotor spins, it also forces the eccentric shaft to rotate, creating a continuous motion.

One of the most significant advantages of rotary engines is their simplicity. With only three main moving parts – the eccentric shaft and two rotors – they are relatively easy to design and maintain. Additionally, since everything in a rotary engine moves in a circular motion, there is minimal reciprocating mass, which allows for higher engine speeds.

Manual transmission rotary engines, such as those used in Mazda's RX-7 series, can reach impressive speeds of up to 9,000 rpm. This high speed is made possible by the rotor's unique design and the engine's ability to maintain a consistent temperature throughout its operation. To mitigate the heat generated during combustion, engineers use coolant jackets wrapped around the engine.

Despite their advantages, rotary engines have several disadvantages. One significant issue is their low thermal efficiency, which results from the long shape of the combustion chamber and the large surface area without much volume. This leads to a low compression ratio and a high amount of wasted heat. Additionally, unburnt fuel can leave the exhaust, further reducing the engine's efficiency.

To address these issues, rotary engines often use two spark plugs per cylinder head. These spark plugs help speed up combustion by spreading the flame more quickly through the long combustion chamber. However, this also means that the engine burns oil, which is injected into the combustion chamber during the intake stroke. The added complexity of burning oil raises concerns about emissions and maintenance.

Another significant challenge facing rotary engines is sealing off the combustion chambers. Since different areas of the rotor housing have different temperatures – cool on top and hot on the bottom – it's difficult to create a reliable seal. To mitigate this, engineers use various techniques, including apex seals and coolant jackets, to maintain an even temperature around the engine.

The compact design and high power output of rotary engines have captivated enthusiasts for decades. While they offer many advantages over traditional piston cylinder engines, their low thermal efficiency and emissions issues ultimately led to their demise as a mainstream automotive solution. Nevertheless, researchers continue to explore new applications for rotary engines, including hybrid and hydrogen-powered variants.

As we move forward in the development of rotary engines, it's essential to address some of the existing challenges. The addition of advanced technologies, such as SKYACTIV X, could help improve efficiency and emissions while maintaining the unique characteristics that make rotary engines so compelling. With continued innovation and research, it's possible that rotary engines will once again find a place in the automotive world.

In conclusion, the rotary engine is a fascinating and complex machine that offers many advantages over traditional piston cylinder engines. While they have their drawbacks, their simplicity, high power output, and compact design make them an attractive option for enthusiasts and engineers alike. As we look to the future, it will be exciting to see how researchers and manufacturers continue to develop and refine this innovative technology.

Finally, I would like to thank Erik Carroll for sending me a link to use in this article. It was a great contribution to the content of this video, and I appreciate his enthusiasm for rotary engines. If you have any questions or comments about rotary engines or any other automotive topic, please feel free to leave them below.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video we are checking out this brilliant 3d printed Mazda Wankel engine now this was designed and created by Erik Harrell and I will include a link to it in the video description and this is just a brilliant 3d print so I want to kind of go through it we're gonna check out the different parts of it talk about how it works talk about the air flow and some of the pros and cons it's just a fascinating build and I really wanted to show it off on Erik's behalf again I've got a link to this in the video description now this particular model is a 1/3 scale 13 BRE W engine it was used in the Mazda rx-7 between 1992 and 2002 and it was actually a twin turbocharged engine it had twin sequential turbos so there's a turbo that attaches right on there and another one as well and this engine actually produced about 255 to 280 horsepower quite impressive coming out of this 1.3 liter especially when you consider the size this thing's only about one cubic foot in volume so let's start with a walkthrough of the engine and talk about the different components on it so this is the front of the engine here here we have the front plate behind that is the first rotor housing it's called the rotor housing because it houses the rotor so there inside you can see the rotor this is kind of the equivalent of the piston in a piston cylinder engine so this rotor will be spinning around within that rotor housing producing power and then we get to our center plate here then we have our second rotor housing so this is a two rotor engine and then we get to our rear plate in the back and then finally the flywheel and this is actually power there's an electric motor to make this thing rotate so you can see we can rotate the rotors inside and we can rotate this flywheel here so once again looking inside of the engine this rotor is ultimately what's powering that flywheel and then sending power from the flywheel to the transmission so this rotor rotates on an eccentric shaft which is in the center here in this eccentric shaft comes all the way from the front plate to that back plate to that flywheel and it's rotating that flywheel it's not actually cut off like you see here it actually extends all the way through the engine here it's just cut off so that you can see inside of this engine but that rotor is going to rotate on that eccentric shaft and ultimately power is perd used by forcing that rotor to rotate so here's what's really cool about this 3d printed model because the rotor actually has a light on it showing us the combustion process so just like a piston-cylinder device has those four strokes intake compression power and exhaust this does those same four things just the difference is it's not a reciprocating mass instead it's rotational and so looking in the engine here you can see that as it rotates over it pulls in that air compresses it you've got your spark plugs right here so that ignites it you have your exhaust it pushes the exhaust out here pulls in that fresh new air fills up this chamber with air and fuel as that air in fuel gets squeezed down your spark plugs fire pushes this rotor to force to rotate and then that exhaust is pressed out the exhaust right here this is where the exhaust port is intake ports are coming in from right here feeding into the chamber now it's not just one chamber that is active at a time in fact there are three chambers as you can see and all of them are simultaneously going through that combustion cycle and so up on the top here you can see the intake stroke which is always occurring within this region then over here you always have the power stroke and it's occurring in this region over here you've got the exhaust coming out right here so you've got intake you compress that air in fuel get over here you hit your spark plugs power stroke pushes this thing over and then the exhaust stroke forces out those exhaust gases and that's occurring in three different locations at the same time you've got that cycle occurring and because there are two rotors so that means you've got six cycles continuously occurring within this engine alright so now let's walk through the air flow for this engine starting with the intake and then ending with the exhaust so the air starts off coming in the intake portion of the turbocharger you're going to feed that air through a filter then to the compressor side of the turbocharger it will be passed out of the turbocharger sent to the front of the vehicle to go through the intercooler and then come back to the intake manifold so here we have the intake manifold it'll be mounted like so with your air coming across and then down through these runners and into the individual rotor housings you can see there are two ports on each side each rotor housing has two ports of air coming in so it's bringing air on the left right side of the rotor so if I rotate this out you can actually see those ports there so there's one port on the left side of this rotor that feeds in air on that side and then you have another port on this side which feeds in air on this side of it and so you can see there's two here in the middle so it actually splits there and one feeds air to one rotor one feeds air to the other rotor you can see that lined up there on the intake manifold so looking inside the rotor here you can see if I shine a light you can see that intake port where the air comes in as that rotor rotates you've got the same thing on this side of the rotor housing so in our center plate where the air will come in right here and then it will pass into it'll be pulled in as this rotor rotates creating a vacuum pulling in that air through that air intake port on both sides so you've got your air which comes in on this side of the rotor as well as on this side of the rotor it goes through that combustion process and then it's forced out this port right here which is the exhaust port so the air will come out of those two exhaust ports go into the exhaust manifold where it then spools up the turbocharger which is attached there so you can see the two ports there for the exhaust to match up with and then it spools up this turbo charger and this turbo charger actually does spin if I blow into the exhaust you can see it rotates there and you can see the intake side spins as well after the exhaust passes through the turbocharger it will exit right here and go towards the back of the vehicle where it will exit through the tailpipe so let's get into the advantages and disadvantages of this engine style and starting with one of the most obvious ones is that this has a great power-to-weight ratio and a great power to volume ratio so this is a 1/3 scale imagine this thing just being about three times as wide and three times as tall it's about one cubic foot and yet it's capable of producing 255 to 280 horsepower out of a 1.3 liter now part of why it makes so much power relative to its displacement is the fact that it has a lot of power strokes for every revolution of this rotor and so the eccentric shaft is geared to the rotor with a three to one ratio so when this rotor rotates just once the eccentric shaft will rotate three times so let's demonstrate that here with the eccentric chef so watch this it's going to rotate one full time around and we'll follow this spot on the rotor so one full time around and now we're here another full time around now we're here another full time around and we're back to where we started so the eccentric shaft rotates three times for every single rotation of this rotor and this rotor has three combustion processes happening simultaneously so let's do a little bit of quick math to explain why this engine cycle is advantageous for creating power versus a four-stroke engine so if you have a four-stroke single-cylinder piston cylinder engine rotating at a thousand rpm a thousand times per minute that four-stroke engine has one power stroke for every two revolutions of the crankshaft so if the engine spinning at a thousand rpm you have five hundred power strokes per minute now in a rotary engine if you're spinning at that same speed the engine is spinning at a thousand rpm that rotor is spinning at a third of that so 333 rpm but you have three combustion phases for every one rotation of that rotor so if the rotor is spinning at 333 rpm you multiply that by three you get a thousand power strokes per minute if the engine is spinning at a thousand rpm so it's a lot like a two-stroke engine where a two-stroke engine rotating at a thousand rpm is also producing a thousand power strokes per minute versus a four-stroke engine which is producing 500 power strokes per minute so often people will kind of compare the displacement of a 1.3 liter rotary engine to a two point six liter piston cylinder engine doubling the displacement because it has twice as many power strokes per engine revolution another advantage of the Wankel engine is just it's very simple design and so there's really only three main moving parts you've got the eccentric shaft and then you've got the two rotors which force that eccentric shaft to rotate also everything is moving in a circle so you have rotational inertia rather than reciprocating mass like you have an epistle cylinder engine so a piston cylinder that Pistons moving up and down within this rotary engine everything's just spinning in a circle and because of that it helps allow for higher engine speeds so the manual transmission rotary engines and these are x7 SRX eights they're spinning up to 9,000 rpm which is a crazy high engine speed very cool and very doable with engine design because everything is rotational you don't have that reciprocating mass going up and down now unfortunately this engine also has quite a bit of disadvantages so first off it has a low thermal efficiency unfortunately due to the design of the combustion chamber the shape of it has a very large surface area without all that much volume so overall you've got a low compression ratio and you've got a lot of surface area to reject heat to so instead of that heat rotating the rotor you're simply losing it as wasted heat also due to the long shape of the combustion chamber you often have unburnt fuel leaving the exhaust which obviously is not that efficient now there are actually two spark plugs used and the reason why they do that is to help speed up combustion make sure you do burn that fuel so once the rotor finishes that compression cycle you've got two spark plugs firing which helps to spread that flame more quickly through the long combustion chamber it also burns oil by design so there are oil squirters within the combustion chamber so during that intake stroke you're also spraying in some oil and that oil is to help seal the combustion chamber you've got apex seals on the corners of that rotor so there's three individual apex seals and you've got oil to help create a seal between the three different chambers but by injecting oil obviously that means you're burning oil and it also means the emissions aren't going to be great because that oil has to leave through the exhaust now speaking of sealing sealing off these combustion chambers is another big problem with these engines and part of the reason for that is that there are different areas with different temperatures within this rotor housing so the top of the rotor is where you always have that intake stroke occurring versus you have that power stroke occurring on that bottom right and your exhaust continuing along the bottom there and because of that you have a cool section on top with a hot section on the bottom metals don't like to be at all these different temperatures when you're trying to seal something and so from a sealing perspective it's quite a challenge with this engine now to help mitigate this you do have coolant jackets wrapped around the engine so that's attempting to create an even temperature around the entire engine that's what you see here in green on the engine those different coolant jackets but overall it's a challenge to create a good seal with these style engines so overall it is a very cool engine super compact lots of power very smooth power delivery unfortunately quite a few disadvantages to it which kind of killed it off especially from an efficiency and an emissions perspective now I'm going to be creating a few more additional videos on rotary engines talking about using hydrogen with it talk about Mazda perhaps applying some SKYACTIV X technology to the rotary engine and bringing it back so some cool stuff that I'll be creating in the future using this model very neat thing here which I again included a link to in the video description big thanks to Erik Carroll for sending me this to use in this video thank you all so much for watching if you have any questions or comments of course feel free to leave them belowhello everyone and welcome in this video we are checking out this brilliant 3d printed Mazda Wankel engine now this was designed and created by Erik Harrell and I will include a link to it in the video description and this is just a brilliant 3d print so I want to kind of go through it we're gonna check out the different parts of it talk about how it works talk about the air flow and some of the pros and cons it's just a fascinating build and I really wanted to show it off on Erik's behalf again I've got a link to this in the video description now this particular model is a 1/3 scale 13 BRE W engine it was used in the Mazda rx-7 between 1992 and 2002 and it was actually a twin turbocharged engine it had twin sequential turbos so there's a turbo that attaches right on there and another one as well and this engine actually produced about 255 to 280 horsepower quite impressive coming out of this 1.3 liter especially when you consider the size this thing's only about one cubic foot in volume so let's start with a walkthrough of the engine and talk about the different components on it so this is the front of the engine here here we have the front plate behind that is the first rotor housing it's called the rotor housing because it houses the rotor so there inside you can see the rotor this is kind of the equivalent of the piston in a piston cylinder engine so this rotor will be spinning around within that rotor housing producing power and then we get to our center plate here then we have our second rotor housing so this is a two rotor engine and then we get to our rear plate in the back and then finally the flywheel and this is actually power there's an electric motor to make this thing rotate so you can see we can rotate the rotors inside and we can rotate this flywheel here so once again looking inside of the engine this rotor is ultimately what's powering that flywheel and then sending power from the flywheel to the transmission so this rotor rotates on an eccentric shaft which is in the center here in this eccentric shaft comes all the way from the front plate to that back plate to that flywheel and it's rotating that flywheel it's not actually cut off like you see here it actually extends all the way through the engine here it's just cut off so that you can see inside of this engine but that rotor is going to rotate on that eccentric shaft and ultimately power is perd used by forcing that rotor to rotate so here's what's really cool about this 3d printed model because the rotor actually has a light on it showing us the combustion process so just like a piston-cylinder device has those four strokes intake compression power and exhaust this does those same four things just the difference is it's not a reciprocating mass instead it's rotational and so looking in the engine here you can see that as it rotates over it pulls in that air compresses it you've got your spark plugs right here so that ignites it you have your exhaust it pushes the exhaust out here pulls in that fresh new air fills up this chamber with air and fuel as that air in fuel gets squeezed down your spark plugs fire pushes this rotor to force to rotate and then that exhaust is pressed out the exhaust right here this is where the exhaust port is intake ports are coming in from right here feeding into the chamber now it's not just one chamber that is active at a time in fact there are three chambers as you can see and all of them are simultaneously going through that combustion cycle and so up on the top here you can see the intake stroke which is always occurring within this region then over here you always have the power stroke and it's occurring in this region over here you've got the exhaust coming out right here so you've got intake you compress that air in fuel get over here you hit your spark plugs power stroke pushes this thing over and then the exhaust stroke forces out those exhaust gases and that's occurring in three different locations at the same time you've got that cycle occurring and because there are two rotors so that means you've got six cycles continuously occurring within this engine alright so now let's walk through the air flow for this engine starting with the intake and then ending with the exhaust so the air starts off coming in the intake portion of the turbocharger you're going to feed that air through a filter then to the compressor side of the turbocharger it will be passed out of the turbocharger sent to the front of the vehicle to go through the intercooler and then come back to the intake manifold so here we have the intake manifold it'll be mounted like so with your air coming across and then down through these runners and into the individual rotor housings you can see there are two ports on each side each rotor housing has two ports of air coming in so it's bringing air on the left right side of the rotor so if I rotate this out you can actually see those ports there so there's one port on the left side of this rotor that feeds in air on that side and then you have another port on this side which feeds in air on this side of it and so you can see there's two here in the middle so it actually splits there and one feeds air to one rotor one feeds air to the other rotor you can see that lined up there on the intake manifold so looking inside the rotor here you can see if I shine a light you can see that intake port where the air comes in as that rotor rotates you've got the same thing on this side of the rotor housing so in our center plate where the air will come in right here and then it will pass into it'll be pulled in as this rotor rotates creating a vacuum pulling in that air through that air intake port on both sides so you've got your air which comes in on this side of the rotor as well as on this side of the rotor it goes through that combustion process and then it's forced out this port right here which is the exhaust port so the air will come out of those two exhaust ports go into the exhaust manifold where it then spools up the turbocharger which is attached there so you can see the two ports there for the exhaust to match up with and then it spools up this turbo charger and this turbo charger actually does spin if I blow into the exhaust you can see it rotates there and you can see the intake side spins as well after the exhaust passes through the turbocharger it will exit right here and go towards the back of the vehicle where it will exit through the tailpipe so let's get into the advantages and disadvantages of this engine style and starting with one of the most obvious ones is that this has a great power-to-weight ratio and a great power to volume ratio so this is a 1/3 scale imagine this thing just being about three times as wide and three times as tall it's about one cubic foot and yet it's capable of producing 255 to 280 horsepower out of a 1.3 liter now part of why it makes so much power relative to its displacement is the fact that it has a lot of power strokes for every revolution of this rotor and so the eccentric shaft is geared to the rotor with a three to one ratio so when this rotor rotates just once the eccentric shaft will rotate three times so let's demonstrate that here with the eccentric chef so watch this it's going to rotate one full time around and we'll follow this spot on the rotor so one full time around and now we're here another full time around now we're here another full time around and we're back to where we started so the eccentric shaft rotates three times for every single rotation of this rotor and this rotor has three combustion processes happening simultaneously so let's do a little bit of quick math to explain why this engine cycle is advantageous for creating power versus a four-stroke engine so if you have a four-stroke single-cylinder piston cylinder engine rotating at a thousand rpm a thousand times per minute that four-stroke engine has one power stroke for every two revolutions of the crankshaft so if the engine spinning at a thousand rpm you have five hundred power strokes per minute now in a rotary engine if you're spinning at that same speed the engine is spinning at a thousand rpm that rotor is spinning at a third of that so 333 rpm but you have three combustion phases for every one rotation of that rotor so if the rotor is spinning at 333 rpm you multiply that by three you get a thousand power strokes per minute if the engine is spinning at a thousand rpm so it's a lot like a two-stroke engine where a two-stroke engine rotating at a thousand rpm is also producing a thousand power strokes per minute versus a four-stroke engine which is producing 500 power strokes per minute so often people will kind of compare the displacement of a 1.3 liter rotary engine to a two point six liter piston cylinder engine doubling the displacement because it has twice as many power strokes per engine revolution another advantage of the Wankel engine is just it's very simple design and so there's really only three main moving parts you've got the eccentric shaft and then you've got the two rotors which force that eccentric shaft to rotate also everything is moving in a circle so you have rotational inertia rather than reciprocating mass like you have an epistle cylinder engine so a piston cylinder that Pistons moving up and down within this rotary engine everything's just spinning in a circle and because of that it helps allow for higher engine speeds so the manual transmission rotary engines and these are x7 SRX eights they're spinning up to 9,000 rpm which is a crazy high engine speed very cool and very doable with engine design because everything is rotational you don't have that reciprocating mass going up and down now unfortunately this engine also has quite a bit of disadvantages so first off it has a low thermal efficiency unfortunately due to the design of the combustion chamber the shape of it has a very large surface area without all that much volume so overall you've got a low compression ratio and you've got a lot of surface area to reject heat to so instead of that heat rotating the rotor you're simply losing it as wasted heat also due to the long shape of the combustion chamber you often have unburnt fuel leaving the exhaust which obviously is not that efficient now there are actually two spark plugs used and the reason why they do that is to help speed up combustion make sure you do burn that fuel so once the rotor finishes that compression cycle you've got two spark plugs firing which helps to spread that flame more quickly through the long combustion chamber it also burns oil by design so there are oil squirters within the combustion chamber so during that intake stroke you're also spraying in some oil and that oil is to help seal the combustion chamber you've got apex seals on the corners of that rotor so there's three individual apex seals and you've got oil to help create a seal between the three different chambers but by injecting oil obviously that means you're burning oil and it also means the emissions aren't going to be great because that oil has to leave through the exhaust now speaking of sealing sealing off these combustion chambers is another big problem with these engines and part of the reason for that is that there are different areas with different temperatures within this rotor housing so the top of the rotor is where you always have that intake stroke occurring versus you have that power stroke occurring on that bottom right and your exhaust continuing along the bottom there and because of that you have a cool section on top with a hot section on the bottom metals don't like to be at all these different temperatures when you're trying to seal something and so from a sealing perspective it's quite a challenge with this engine now to help mitigate this you do have coolant jackets wrapped around the engine so that's attempting to create an even temperature around the entire engine that's what you see here in green on the engine those different coolant jackets but overall it's a challenge to create a good seal with these style engines so overall it is a very cool engine super compact lots of power very smooth power delivery unfortunately quite a few disadvantages to it which kind of killed it off especially from an efficiency and an emissions perspective now I'm going to be creating a few more additional videos on rotary engines talking about using hydrogen with it talk about Mazda perhaps applying some SKYACTIV X technology to the rotary engine and bringing it back so some cool stuff that I'll be creating in the future using this model very neat thing here which I again included a link to in the video description big thanks to Erik Carroll for sending me this to use in this video thank you all so much for watching if you have any questions or comments of course feel free to leave them below\n"