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.

http://www.bradlanders.com/2011/06/28/whats-up-with-this-wav...

What’s up with this Wave Disk engine?
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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:

* The friction involved with all the moving parts required to regulate the otto-cycle
* The thermodynamic characteristics of the engine's design

From here, the conversation gets pretty complex. This is where "I'm no expert" becomes very apparent. If you're interested in further reading, google the Carnot cycle.

Here's my layman's understanding of the limits:

_Friction_ - The engines in our cars experience a lot of friction. Ever use a syringe? The principle mechanical operation of your car engine isn't all that different. The piston experiences friction as it moves up and down inside the cylinder, and in addition, it must force air in and out of the cylinder through small-ish holes regulated by valves. Additional friction is present in all the rotating parts; and there are many. Lots of time, money, and effort has been spent decreasing friction and the resistance of air moving in and out of the engine. Virtually every performance mod you can do to your car's engine has to do with these two limiting factors. The inherent mechanical complexity of your car's engine prevents it from reaching high levels of efficiency.

_Thermodynamic characteristics_ - With this type of engine, we're relying on the fact that we're going to draw in a (hopefully) cold mass of air mixed with fuel, then light it on fire and harness the energy produced by its expansion. The problem is, we're doing this deep inside a giant hunk of metal that is constantly soaking up a portion of this heat. This stolen heat energy must be dissipated -- lest our engine begin to overheat -- so we use a huge fan to blow across a radiator full of water that is constantly pumped through the engine. Both the fan and the water pump require energy to operate. Additionally, the piston moves only a short distance, so we're not harnessing the entire heat cycle; only a small portion of it. The gasses that come out of the exhaust are still very hot. If you haven't gotten the picture by now, the ICE leaks energy all over the place.

Despite the major limitations outlined above, this type of engine works well for us because it produces mechanical energy in a range that is easy to use. A typical ICE found in your car "idles" at around 800 RPM and can spin up to 5,000 RPM (much higher in many cases). This rate of rotation is easily geared to match the required traveling speed of an automobile. This is not coincidence. Using gears to change the rotational speed of mechanical energy means additional mass and friction in the driveline. The engine's energy must be used to accelerate all that mass up to traveling speeds and overcome the increased friction. Overall, the ICE is a good fit for the automobile.

That's just about all I have to say about the venerable ICE. It's a fine piece of engineering that has served us well over the years, but I suspect its time is coming to a close.

### Ride the wave dude ###

As the wave disk engine is yet to be released, details aren't exactly plentiful. Although, it does share a lot of commonalities with another type of engine that has been around since the mid-twentieth century: the turbine. It's probably easiest at this point to explain how the turbine differs from the ICE found in your car, rather than tackle the wave disk head on.

Coincidentally, a turbine is also an internal combustion engine (ICE), but I'm going to refer to it more specifically as a turbine, and continue to refer to your car engine as an ICE. That ought to bring the pedants out in force! Likewise, HowStuffWorks has a good article on "how a turbine works":http://science.howstuffworks.com/transport/flight/modern/tur....

A turbine engine is, in ways, far simpler than a traditional ICE; and in other ways, more sophisticated. In operating principle, a turbine is a series of fans oriented axially inside a housing. Air is drawn in from one end, compressed through a series of fan "stages", then mixed with fuel, ignited, and shot out the other end, passing through another series of fans.

All these fans are attached to a shaft. The pitch of the fans on the way in progresses to compress the air before it is mixed with fuel and ignited. The fans on the aft end of the turbine are like a windmill that harnesses the breeze. This breeze happens to be thousands of degrees Fahrenheit. The burning fuel air exits the rear of the turbine, rather than the front, because expanding gasses are lazy and generally like to leave through the nearest/least crowded exit. Since all the air is moving toward the back, the pressure at the front of the engine is higher, thus the gasses are happy to exit out the rear.

So you could think of a turbine like a desk fan blowing on a pinwheel, only instead of an electric motor powering the fan, there's a giant ball of fire in-between, and the pinwheel is hooked up to a shaft that drives the desk fan. I'm probably losing you here.

Let's talk efficiency and limiting factors. Turbines are generally more efficient than the ICE in your car because of a few mechanical advantages:

_Fewer moving parts_ - Well, maybe not fewer (there are a lot of fans), but simpler. Turbines are typically constructed of one or two shafts with a series of fans, and a burner.

_Conservation of motion energy_ - All the parts inside a turbine rotate consistently. They don't change directions as the turbine operates. The pistons in your cars engine have to change from up to down in a very abrupt change of direction. This is not efficient.

_Less friction_ - The fans inside a turbine rotate on a shaft. They compress the air as it moves along by having very, very close tolerances with the tube shape of the turbine, but they don't actually touch. Also, there are no valves and camshafts to operate.

Sounds good, huh? Turbines for everyone!

(continued on my blog...)

http://www.bradlanders.com/2011/06/28/whats-up-with-this-wav...