
Wave Disk Engine Could Be 3.5 Times More Efficient Than Combustion Engines - DanielN
http://nextbigfuture.com/2011/03/wave-disk-engines-could-be-35-times.html
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samatman
The HN headline for the article is terrible. The Wave Disk engine is a
combustion engine, albiet one of novel design. It is a commonplace among
engine designers that a combined turbine-electric system will be higher
efficiency than a reciprocating engine is capable of; the Wave Disk appears to
be a turbine engine with some slick combustion dynamics. That's great, but
fuel is being combusted in any case.

~~~
DanielN
I apologize for that. This is pretty far from my area of expertice. I guess a
more appropriate titled would be "more efficient than a traditional combustion
engine".

Either way thanks for improving my understanding of the system.

~~~
bradleyland
"More efficient than an otto-cycle, reciprocating, piston-in-sleeve, internal
combusion engine" probably would have put you over the title length limit
anyway :)

~~~
rbanffy
Be fair. It's probably more efficient than Wankel engines too.

~~~
Gaussian
Ach. You beat me to the Wankel reference.

I do feel like we've seen this movie before. The problem with rotary engines,
usually, is that their round shape and operation, though efficient, can make
sealing difficult. So they can be plagued by emissions issues when it comes to
the wear-and-tear of everyday use.

But it would be sweet if this engine licked all of that.

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aidenn0
An internal combustion engine based on rotation rather than reciprocation that
reduces complexity for many advantages. I think I've heard this story before.
Oh yeah:

<http://en.wikipedia.org/wiki/Rotary_combustion_engine>

The Wankel engine is by far the most mature of those, and it's a lot more
complicated in 3d than in a 2d cross-section. Sealing and such are an issue.
Mazda has really done a lot of good things with them, and their power-weight
is way better than your average 4-stroke, but it is still a niche product.

I'm not saying the Wave Disk engine isn't going to be great, I'm saying you're
not going to see one of these in your car in the next 20 years, and 20 years
from now, who knows what the "average car engine" is going to be and how well
the wave disk engine will compare to it.

~~~
pge
There is an argument to be made that the shift to hybrid cars opens the door
for a lot of engine design variations that did not work in the past. In a
normal car, the engine drives the wheels directly which puts a lot of
constraints on engine performance parameters (e.g. needs to be able to
generate a lot of torque at slow speed, needs to operate over a wide RPM
range, etc). Today's engines are a compromise to meet those requirements. If
you decouple the engine from the wheels (as in some newer hybrids) and just
use the engine as a generator, it can be run at its optimum RPM all the time,
and does not need to be able to generate high torque.

So, I think it is feasible that we'll see some movement away from the 4 stroke
otto cycle that is standard today, and some ideas that didnt work out in the
past might work out better now.

~~~
rbanffy
Can I dream with a Ford Nucleon? ;-)

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drcode
...and combustion engines in the future "could be" 3.5 times more efficient
than they are now, as well.

How efficient are current wave disk engines? Any claim about a future, non-
existent engine is just hot air. (In fact, the current wave disk engines
probably generate way too much hot air already, or their current efficiency
would be featured more prominently in the article.)

~~~
dexen
For every cycle and construction, there is theoretical efficiency limit
inherent to it. Implementations will approach that, more or less
asymptotically, but can't exceed.

A novel cycle and construction may leave more headroom for improvement, even
if first implementation aren't particularly efficient.

IIRC turbines are usually highly efficient, but only in a narrow band, near
maximum output; at low RPM they literally suck. Perhaps a novel construction
could widen the gap considerably.

~~~
bigiain
That's correct , but its possible that the time has come when narrow-band-
efficiency is an appropriate technology.

A "typical" car with a piston engine directly mechanically connected to the
wheels needs an engine with a wide rpm and power output range.

A hybrid electric drivetrain doesn't necessarily need that - if a motor that
could run at 60% efficiency but only at 8725 +- 15 rpm existed, it'd be
useless for a traditional car, but it'd be easy to integrate that into a
hybrid electric vehicle...

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gte910h
I'm curious to see the real prototype engine they're getting out this year.

Basically: This is only appropriate for use in hybrid engines, as the range of
efficiency is very narrow.

That said, if it works, this would be terrific for further upping the
efficiency of hybrids.

~~~
lutorm
It sounds like it has the same disadvantages as a gas turbine, then. It would
have been helpful if they had contrasted it to a gas turbine instead of to a
piston engine. Theoretically, a gas turbine has huge advantages over a normal
ICE. Yet, there aren't any cars powered by gas turbines...

~~~
rosser
It's only a concept car, but Jaguar's C-X75 is twin gas-turbine charged and
electrically powered.

[http://blogs.insideline.com/straightline/2010/09/jaguar-
c-x7...](http://blogs.insideline.com/straightline/2010/09/jaguar-
c-x75-concept-all-wheel-drive-jet-turbine-electric-supercar-fromjag-updated-
with-video.html)

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VladRussian
sounds like a variation of gas turbine in disguise. Any implementation that is
cheaper and simpler that existing gas turbines, yet reaches its high
efficiency and power/weight ratio would be just great.

>The resulting sudden build-up of pressure in the chamber generates a shock
wave

that makes me doubtful about longevity of the engine if the shock wave touches
the metal.

~~~
jonah
> that makes me doubtful about longevity of the engine if the shock wave
> touches the metal.

Sure. But what about the common reciprocating engine style. There's a lot of
mechanical strain with the pistons being yanked back-and-forth 1000s of
times/second not to mention the energy lost in counteracting momentum.

~~~
VladRussian
considering the upvote to your comment, there is at least another HN reader
who thinks that there are 60K+ rpm reciprocating engines and who don't know
what detonation sensor, octane number or cavitation are about... Hope you know
your Python better :)

~~~
jonah
Heh, good catch. Should have said 1000s of times per minute.

60k is 3x the RPM of an F1 motor.

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sliverstorm
Fun fact: Otto cycle has been taken to ~30% efficiency, IIRC.

3.5 * .30 = ???

~~~
seles
the article claims standard car engine efficiency is 0.15, so 3.5*0.15 = 0.45

~~~
aidenn0
They really cheat with that number. They are using engine-to-wheels
efficiency, but then talk about the wave-disk in a hybrid presumably with no
drive-train losses. A gasoline engine running over a much smaller RPM range
will run _much_ more efficient than 15%.

An efficient car may run at about 18% on average (hence the 15% after external
losses), but quite possibly have a peak efficiency of 30%

Also, they compare to a gasoline Otto cycle engine. The diesel cycle is more
efficient than the Otto cycle. A cars turbocharged diesel may run nearly 30%
average efficiency, and peak efficiency in the 40s. (The ratio of peak/average
eefficiency in diesel engines tends to be closer to unity than in gasoline
engines).

There are actual operating now diesel engines operating at over 50%
efficiency, but they are not the sort of thing you would put in your car (more
the sort of thing where your car would fit inside the engine).

[edit]I wanted to find info on the prius before posting this, but was unable
to. I finally did, and the complexity of the drivetrain is to (among other
things) maximize the amount of the time that the engine is in it's peak
efficiency area of 230g/kWh which is roughly an efficiency of 33%. Since the
article specifically talks about running the engine in a hybrid comparison,
this is apples-to-apples, and it is less than a 2x improvement, not 3.5x

[edit2]The Prius is not a vanilla Otto cycle, but it's pretty close. I really
think of it as more of a Miller cycle than an Atkinson, but in any event it's
a 4-stroke spark-ignited reciprocating piston engine.

~~~
kwantam
Note also that the Prius engine employs the Atkinson cycle rather than the
Otto.

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justin_vanw
Anything can be anything, as long as it is purely conjecture.

To all of you voting up articles like this: you suck.

