The rotary engine was found to be less efficient than piston engines. I think it's because the streamlined approach of intake an exhaust needs to be babysat, with a chamber and an object to (Make exhaust go away 100%) and (Make fresh air-fuel mixture come in) then a timed predictable ignite.
Is the wave disk engine just a modification of the Turbine engine?
i would guess that it's hard to get a good (reliable, long-life) seal between the rotating part and the upper surface (i don't think this is much like a wankel engine, but it probably does share that problem).
also, it looks like it's supposed to spin at a constant, high speed - that might imply high pitched whine (see someone else's comparison with a gas turbine).
The wave engine has neither spark plugs nor a compression cycle. It appears to achieve combustion by causing a localized region of sufficient pressure, this in turn is created by blocking the moving fuel air mixture and letting inertia pile the molecules up in one spot, more or less.
I wrote a blog post on the topic. I'm somewhere between a layman and an expert when it comes to this type of thing. I tried posting the whole thing here, but it's too long. What follows is an excerpt, with the balance of the article available on my blog.
What’s up with this Wave Disk engine?
=====================================
I say this a lot, but "I'm no expert." By this I mean that an engineer who specializes in this field would rip my little essay apart for technical inaccuracies and abuse of terminology. Fortunately for me, many people know less than I do and will not be similarly offended by my ham fisted treatment of the subject matter I'm about to attack.
Having said that, I've always been a gear head of sorts, and being a hacker, I've always been interested in non-traditional engine designs, so the wave disk engine simultaneously interested me and set off my bullshit meter. Most of the press coverage sucks wind. There isn't a whole lot of appetite for loosely-detailed explanations of complex engineering phenomenon, but that won't stop me from rambling on here. So, if you're up for it, get comfortable in your chair and let's talk about this new fangled wave disk engine.
The wave disk motor has hit "Hacker News":http://news.ycombinator.com/item?id=2704614 a few times, so I've had some time to look in to it. I'm going to take a few kilobytes of text here explain my understanding of this new technology, which lies somewhere between a complete layman and an actual engineer. Hopefully it will help everyone understand a little more about this motor and why it is, indeed, significant.
Introducing, the engine in your car
The engine in your car is the most common type of gasoline powered engine on the planet. The long form description of the engine in your car would be something like: piston-in-sleeve, reciprocating, otto-cycle, internal combustion engine.
Let's break that down:
_Piston-in-sleve_ - Inside the engine are cylinders, inside which a piston moves up and down. This up and down motion compresses the air/fuel mixture, which is ignited by a spark. The rapid expansion of gasses in this sealed compartment are the basis of energy production in this type of engine.
_Reciprocating_ - The piston that moves up and down is attached to a crank. This is the mechanism that converts the up/down motion of the pistons to rotating motion. It is not unlike a bicycle crank, where the pistons would be your legs moving up and down.
_Otto-cycle_ - Otto-cycle is frequently referred to as 4-cycle. It defines the steps required to draw the air/fuel mixture in to the cylinder, compress it, ignite it, then expel it... repeat.
_Internal combustion engine_ - Basically this means that the fire occurs inside the engine, as opposed to outside. Steam engines are a good example of external combustion engines. Also look up a Stirling engine for more fun times.
Google any of these terms and you'll get more info than you can read in an afternoon. If you want a good overview, "HowStuffWorks has a nice one":http://auto.howstuffworks.com/engine1.htm.
For the rest of the time here, I'm going to simply refer to this type of engine as an ICE (internal combustion engine). There are other types of ICE other than otto-cycle, but I'd like to keep it simple.
Despite all the complex engineering elements outlined above, the ICE operates on some basic underlying principles that you learned in primary school science class: if you heat something up, it's volume increases. The burning fuel/air mixture is a simple means of heating the mass of gas inside the combustion chamber. Because the volume expands as it is heated, it forces the piston down.
The efficiency of this type of engine is limited by certain factors:...
Ironically, it looks like hnsearch isn't taking full advantage of the hnsearch api.
It appears to be just doing a text search for "discovery.com"; if there's a way to search by submission domain on hnsearch, I'm not seeing it at a quick glance.
Was that a quote from the article? It now says "Researchers estimate the new model could shave almost 1,000 pounds off a car's weight currently taken up by conventional engine systems.". Still no additional explanation though.
Still, even if we're talking about total savings for the car, 1000 pounds is a hell of a lot, and I'm not sure I buy it. For reference, that's 3x the weight of an average V6 (or some light V8s), so it would have to remove a lot and add nothing back.
I found an engine weight list here that seems to be legitimate:
They mention "a prototype gasoline engine that requires no transmission, crankshaft, pistons, valves, fuel compression, cooling systems or fluids." So maybe add the weight of the engine plus the transmission and extra fluids required for both?
Extrapolating from the article there's no transmission or cooling system either - that probably doesn't get you to 1000 pounds, but removing the structure which supports those heavy components might get you close.
From the article: "However, researchers at Michigan State University have built a prototype gasoline engine that requires no transmission, crankshaft, pistons, valves, fuel compression, cooling systems or fluids."
I think they considered all these parts when calculating weight savings.
OK - transmission and 'cooling system and fluids' are the only parts of that that aren't already counted in the engine, and with cooling system and fluids that's already being generous. So we're talking an engine that doesn't need a transmission and runs cool.
Hmmm.
Transmission often counts the differential, without which you can't very well turn corners. You're going to need a reverse gear at minimum and a big part of the point of a transmission is to let you keep the engine in an optimally efficient rev range, so I suspect it'll still gain one.
No radiator? Possible, but to productionise it it'll have to be able to run in both Siberian and Saharan conditions. They're both a regular part of manufacturer sign-off tests for road cars, that it can handle extreme cold with lots of short runs to stop it warming up properly and extreme heat with lots of long runs and soak tests to stop it cooling properly. Personally, I'd expect it'll gain a cooling system.
So, even if the gearbox, diff, radiator and all associated fluids weighed 1,000lbs (unlikely I think), I don't think they could gain their weight quota because I doubt they can really eliminate them.
He designs an engine system. He scraps gearbox and transmission and replaces it with generator and electric motors. At 1:04 he says he will just stick the generator at the back and worry only about producing the required power.
Right, he says you will need to have electric motors to at least assist (hybrid technology) with rapid acceleration. Apparently this engine is probably very efficient at a fixed speed/rpm, and doesn't provide the torque of an ICE.
> The Wave Disk Generator uses 60 percent of its fuel for propulsion; standard car engines use just 15 percent. As a result, the generator is 3.5 times more fuel efficient than typical combustion engines.
I'm skeptical.
Thermodynamic limits apply. While piston engines aren't near the limits, I'm pretty sure that they're around 50% of the limit and would be very surprised if this engine is over 80% of carnot.
So, the only way this engine can be 2x as efficient is if it runs at a significantly higher temperature (which moves the limit).
And, the only way that it can run without a transmission is if it has a very wide operating range. That's hard to do with combustion. And, unless the engine is both reversible and has torque at zero RPM, they'll need both a clutch and a reverse gear.
If they use it to run a generator, they need to account for the electric motor, said generator, and maybe batteries. See diesel-electric locomotives. The prius combines the electric motor and the generator, but needs a transmission.
50% sounded like a lot to me so I checked wikipedia, according to which, most internal combustion engines have an average efficiency of 18-20%. So I guess it could be true if the Wave Disk Generator lives up to those promises.
> 50% sounded like a lot to me so I checked wikipedia, according to which, most internal combustion engines have an average efficiency of 18-20%.
From the wikipedia article that you cited: "Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20%."
I wrote that IC engines are running about 50% of the thermodynamic limits because 18/37 is around 50%.
18x2 is about 37, so there's no way for wave engines to be more than 2x as efficient as current engines unless they run at much higher temperatures. Since the relevant temperature is determined by the fuel....
Getting close to the thermodynamic limit is really hard.
You didn't read the wiki article very carefully
The 18-20% is of the total energy in the fuel. Heat engines, which includes both wave and piston engines, are subject to thermodynamic limits. The thermodynamic limits tell us the maximum efficiency, which is about 40% for the temperature at which ther
28 comments
[ 2.8 ms ] story [ 74.7 ms ] threadhttp://peswiki.com/index.php/Directory:Wave_Disk_Engine
Seems to be a new take on the Wankel rotary engine:
http://en.wikipedia.org/wiki/Wankel_engine
The rotary engine was found to be less efficient than piston engines. I think it's because the streamlined approach of intake an exhaust needs to be babysat, with a chamber and an object to (Make exhaust go away 100%) and (Make fresh air-fuel mixture come in) then a timed predictable ignite.
Is the wave disk engine just a modification of the Turbine engine?
http://en.wikipedia.org/wiki/Turbine
also, it looks like it's supposed to spin at a constant, high speed - that might imply high pitched whine (see someone else's comparison with a gas turbine).
http://www.bradlanders.com/2011/06/28/whats-up-with-this-wav...
What’s up with this Wave Disk engine? =====================================
I say this a lot, but "I'm no expert." By this I mean that an engineer who specializes in this field would rip my little essay apart for technical inaccuracies and abuse of terminology. Fortunately for me, many people know less than I do and will not be similarly offended by my ham fisted treatment of the subject matter I'm about to attack.
Having said that, I've always been a gear head of sorts, and being a hacker, I've always been interested in non-traditional engine designs, so the wave disk engine simultaneously interested me and set off my bullshit meter. Most of the press coverage sucks wind. There isn't a whole lot of appetite for loosely-detailed explanations of complex engineering phenomenon, but that won't stop me from rambling on here. So, if you're up for it, get comfortable in your chair and let's talk about this new fangled wave disk engine.
The wave disk motor has hit "Hacker News":http://news.ycombinator.com/item?id=2704614 a few times, so I've had some time to look in to it. I'm going to take a few kilobytes of text here explain my understanding of this new technology, which lies somewhere between a complete layman and an actual engineer. Hopefully it will help everyone understand a little more about this motor and why it is, indeed, significant.
Introducing, the engine in your car
The engine in your car is the most common type of gasoline powered engine on the planet. The long form description of the engine in your car would be something like: piston-in-sleeve, reciprocating, otto-cycle, internal combustion engine.
Let's break that down:
_Piston-in-sleve_ - Inside the engine are cylinders, inside which a piston moves up and down. This up and down motion compresses the air/fuel mixture, which is ignited by a spark. The rapid expansion of gasses in this sealed compartment are the basis of energy production in this type of engine.
_Reciprocating_ - The piston that moves up and down is attached to a crank. This is the mechanism that converts the up/down motion of the pistons to rotating motion. It is not unlike a bicycle crank, where the pistons would be your legs moving up and down.
_Otto-cycle_ - Otto-cycle is frequently referred to as 4-cycle. It defines the steps required to draw the air/fuel mixture in to the cylinder, compress it, ignite it, then expel it... repeat.
_Internal combustion engine_ - Basically this means that the fire occurs inside the engine, as opposed to outside. Steam engines are a good example of external combustion engines. Also look up a Stirling engine for more fun times.
Google any of these terms and you'll get more info than you can read in an afternoon. If you want a good overview, "HowStuffWorks has a nice one":http://auto.howstuffworks.com/engine1.htm.
For the rest of the time here, I'm going to simply refer to this type of engine as an ICE (internal combustion engine). There are other types of ICE other than otto-cycle, but I'd like to keep it simple.
Despite all the complex engineering elements outlined above, the ICE operates on some basic underlying principles that you learned in primary school science class: if you heat something up, it's volume increases. The burning fuel/air mixture is a simple means of heating the mass of gas inside the combustion chamber. Because the volume expands as it is heated, it forces the piston down.
The efficiency of this type of engine is limited by certain factors:...
http://news.ycombinator.com/item?id=2337237
Also:
http://news.ycombinator.com/item?id=2422867
http://news.ycombinator.com/item?id=2424987
So HN Search still misses some posts. I searched for discovery.com before submitting - got two links from 1 and 2 years ago, but not this one.
It appears to be just doing a text search for "discovery.com"; if there's a way to search by submission domain on hnsearch, I'm not seeing it at a quick glance.
For example: http://shomi.associatedtechs.com/#submissions+from+news.disc...
http://www.hnsearch.com/search#request/all&q=news.discov...
We're indexing the full domain name though we might want to change that.
Have they come up with a working prototype yet?
Erm... are there any conventional engines that weigh 1000 pounds to begin with? Even high end V8s aren't that heavy. I wonder what they mean by that.
"Researchers estimate the new model could shave almost 1,000 pounds off a car's weight currently taken up by conventional engine systems."
A somewhat different statement, though I still share your skepticism.
(http://peswiki.com/index.php/Directory:Wave_Disk_Engine)
Still, even if we're talking about total savings for the car, 1000 pounds is a hell of a lot, and I'm not sure I buy it. For reference, that's 3x the weight of an average V6 (or some light V8s), so it would have to remove a lot and add nothing back.
I found an engine weight list here that seems to be legitimate:
http://fixrambler.com/engineweightchart.txt
On the other hand, I don't think this would apply to cars with 25 kilowatt engines - a 1958 VW beetle only weighed 1600 pounds [http://www.conceptcarz.com/vehicle/default.aspx?carID=10196&...]
I think they considered all these parts when calculating weight savings.
Hmmm.
Transmission often counts the differential, without which you can't very well turn corners. You're going to need a reverse gear at minimum and a big part of the point of a transmission is to let you keep the engine in an optimally efficient rev range, so I suspect it'll still gain one.
No radiator? Possible, but to productionise it it'll have to be able to run in both Siberian and Saharan conditions. They're both a regular part of manufacturer sign-off tests for road cars, that it can handle extreme cold with lots of short runs to stop it warming up properly and extreme heat with lots of long runs and soak tests to stop it cooling properly. Personally, I'd expect it'll gain a cooling system.
So, even if the gearbox, diff, radiator and all associated fluids weighed 1,000lbs (unlikely I think), I don't think they could gain their weight quota because I doubt they can really eliminate them.
I'm skeptical.
Thermodynamic limits apply. While piston engines aren't near the limits, I'm pretty sure that they're around 50% of the limit and would be very surprised if this engine is over 80% of carnot.
So, the only way this engine can be 2x as efficient is if it runs at a significantly higher temperature (which moves the limit).
And, the only way that it can run without a transmission is if it has a very wide operating range. That's hard to do with combustion. And, unless the engine is both reversible and has torque at zero RPM, they'll need both a clutch and a reverse gear.
If they use it to run a generator, they need to account for the electric motor, said generator, and maybe batteries. See diesel-electric locomotives. The prius combines the electric motor and the generator, but needs a transmission.
http://en.wikipedia.org/wiki/Internal_combustion_engine#Ener...
From the wikipedia article that you cited: "Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20%."
I wrote that IC engines are running about 50% of the thermodynamic limits because 18/37 is around 50%.
18x2 is about 37, so there's no way for wave engines to be more than 2x as efficient as current engines unless they run at much higher temperatures. Since the relevant temperature is determined by the fuel....
Getting close to the thermodynamic limit is really hard.
You didn't read the wiki article very carefully
The 18-20% is of the total energy in the fuel. Heat engines, which includes both wave and piston engines, are subject to thermodynamic limits. The thermodynamic limits tell us the maximum efficiency, which is about 40% for the temperature at which ther