

Efficient Rotary Engine Lands Million-Dollar Darpa Contract - craigjb
http://www.popularmechanics.com/military/research/a15233/liquidpiston-darpa-contract/

======
digitalzombie
Did they fix the reliability and oil consumption for Rotary? The rx8 ate a lot
of oil cause the oil lubricating it evaporates. Also the Rx7 rubber hoses
tends to wear down over time.

While the rotary did won Le Man 24 hr endurance race, it is still plagues with
problem. These problems isn't because Pistons are better but because Pistons
had tons of time refining it. Rotary so far have been neglected and it seems
like EV/battery technology will be the future while hybrid is just an
intermediate step between oil and electric.

Another interesting engine that GM tried was Turbine, jet engine for cars. It
sound like a vacuum cleaner.

~~~
brc
Mazda rotary engines are designed with oil injection to lubricate the seals -
they are designed to consume oil.

Rotaries, properly cared for, are a reliable engine with fantastic power
delivery and small size. It's a shame they are plagued with high fuel
consumption which limits their usefulness in anything but sports and racing
applications.

If you read the article this is not a conventional wankel rotary - the rotor
design looks like a wankel housing, so it's flipped around.

~~~
watmough
Reputedly, if you own an RX-7 or RX-8, you should spin the engine up to 9k
revs at least once every trip... lest carbon deposits build up and wreak
havoc.

I can't imagine a technology like this is that well suited to constant and
relatively low power delivery.

~~~
busterarm
Not entirely accurate. The 5th and 6th ports don't open up until 3800 and
ideally you want to slightly redline it for a few seconds, but you definitely
want to at least open up those ports. You can also get away with not doing it
for a while, but you shouldn't.

on a pre-89 that (factory) redline is at 7k, 8k on 89-. RX8s you have to hit
9k.

This does make it hard not to speed in an RX7, especially if you've done a
little bit of work to it - not so much in the RX8.

------
aidenn0
I know the intent for this engine isn't for road-legal cars, but...

This runs on Diesel, and advertises a low-temperature exhaust; can someone who
knows more tell me if diesel's need hot exhaust for emissions reduction? I
know that they tend to use EGR for NOx, but every car with a diesel I've seen
still has a catalytic converter to do _something_.

------
mattlutze
The benefit and trouble with rotary engines is their reliability -- fewer
moving parts means they'll generally fail less during their life cycle, and
running them under higher loads / higher output, within their specifications,
will generally not reduce the life expectancy (as in, run a 100HP rotary
continually at 30 or 100, nearly the same running life).

But they will have a shorter overall lifespan. That large moving inner chamber
and the outer chamber walls around it will wear down, and when they fail you
replace a significant amount of that combustion chamber (or just junk the
entire motor).

It's a neat application of the technology, and particularly in contexts where
either the motor is going to run for long periods at a specific speed or not
be used all the time, it could make a great option for power generation.

~~~
busterarm
2nd Generation Turbo RX7 owner here. Rebuilt 13B engines before.

The reliability of the engine itself is way misunderstood. They aren't more or
less reliable than any other engine (okay, they're way more reliable than
Subaru engines...).

The problems are with heat and lubrication. The early RX8s had a flawed
design. 2nd and 3rd Gen RX7s had problems with their OMPs and terrible
electrical problems. 2nd gens have really weak alternators stock. Turbos
usually fail before engines do.

Honestly the engine itself is awesome. Yes, if you lose a seal it will screw
your engine (but usually the housings & rotors are salvageable). Piston
engines throw rods and screw your whole car. If you bypass the OMP and run
premix and actually do proper maintenance on your car, they will last. My 10AE
has over 110k miles on it and has not blown up yet -- probably has another
another 40k on it before it'll be ready for a rebuild. I still am on the stock
OMP (it's an S4).

~~~
yason
_My 10AE has over 110k miles on it and has not blown up yet -- probably has
another another 40k on it before it 'll be ready for a rebuild._

That's really low. I don't think I've ever bought a car with only 110k miles
on it...

~~~
snowwindwaves
in canada it is unusual to see cars with more than 300,000 km on them, so a
vehicle with 176,000 km is more than half way to being really well used, not
"really low" mileage.

I had a toyota land cruiser with 365,000km on rebuilt engine and 800,000 km on
the body though.

Where do you live that 110k miles is low mileage? How many miles is a lot to
you? How/why are people driving that much?

~~~
eric_h
> in canada it is unusual to see cars with more than 300,000 km on them

That's largely because of the need to salt roads in the canadian winters -
yearly, excessive exposure to salt water drastically limits the possible
lifetime of a car. The further away from cold weather requiring salted
roadways you get, the longer cars last.

~~~
snowwindwaves
So in developed countries that don't have icy winter roads most people are
driving cars with more than 300,000 km on them?

I'm really curious where the parent lives that people are investing so much in
the longevity of a vehicle. By the time they get to 300,000 km even if they
aren't rusty they are usually 20 years old and things like drivetrain start to
go and the vehicle is not worth the cost to keep up the required maintenance.

~~~
rinon
I can attest that this is not unheard of in southern california. 1995 cars are
driving all over the place. Cars seem to have a lifecycle where they get sold
to poorer owners with more and more miles piling on, and only get junked when
they are beyond repair. Even a 150-200k miles car is worthy of selling on
craigslist (for super cheap of course, but there are plenty of buyers).

Now to be fair, SoCal has a rather unique and essential car culture, so this
is probably an outlier as far as "most" cities go.

------
x0054
From Another Article: The compact design of LiquidPiston's lab engine
currently tips the scales at 80 lbs for the 40-hp model. It would weigh less
than 50 lbs in production, the company claims, far less than a comparable
40-hp diesel that would tip the scale at around 400 lbs. [1]

How on earth do you get a 400lb diesel engine that ONLY produces 40HP. First,
when comparing engines for power production, you should really talk about kW
production capability, not HP. Engine's HP is only half the story, you also
have to talk about it's torque.

I know rotary engines are a cool technology, but something about this smells
like BS.

[1][http://www.popularmechanics.com/cars/a8174/liquidpistons-
hyp...](http://www.popularmechanics.com/cars/a8174/liquidpistons-hyper-
efficient-engine-turning-the-rotary-inside-out-13817971/)

Edit: citation added

~~~
NickNameNick
If they're talking about a generator that's expected to run at its peak power
all the time, then I'd expect it to be heavier than an automotive engine that
only hits peak power intermittently.

and 40 hp is 29.8kW. they're both measures of power. you don't need to know
the torque to make the conversion.

------
dietrichepp
The efficiency is mentioned, but I don't see any numbers telling how efficient
it is, which is what I really wanted to hear. (Just numbers about how small it
is.)

~~~
Aoyagi
_The cycle, which combines high compression ratio (CR), constant-volume
(isochoric) combustion, and overexpansion, has a theoretical efficiency of 75%
using air-standard assumptions and first-law analysis. This innovative rotary
engine architecture shows a potential indicated efficiency of 60% and brake
efficiency of >50%._

From [http://liquidpiston.com/technology/technical-
papers/](http://liquidpiston.com/technology/technical-papers/)

------
negativity
This is a version of a Wankel Engine, right?

[https://en.wikipedia.org/wiki/Wankel_engine](https://en.wikipedia.org/wiki/Wankel_engine)

Originally invented and patented way back in 1929.

~~~
tim333
Not a Wankel:

[http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpi...](http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpiston-02-1012-de.jpg)

------
raverbashing
A better chance at Darpa than selling it to the doofuses at the big motor
companies, where it would certainly be shelved.

