# Improved Wankel engine design

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#### Winston

##### Lorenzo von Matterhorn
Hope this pans out:

https://liquidpiston.com/news/media-coverage/

[video=vimeo;64911927]https://vimeo.com/64911927[/video]

From various sources:

Its X1 engine is a simple machine with just three moving parts and thirteen major components, but it aims to raise thermal efficiency from the 20 percent of a normal gas engine to more than 50 percent, with drastic reductions in weight and size. How? By wasting much less energy during the course of an combustion cycle.

"We stretched the performance curves in every direction to get much higher efficiency," said Alec Shkolnik, President and CEO of LiquidPiston, "We took the best parts of many different thermal cycles and combined them." The design is theoretically capable of 75 percent thermal efficiency, but the group is targeting 57 percent in real world applications, still a huge jump.

The basic idea is similar to a Wankel rotary, but turned on its head. Where the rotor holds the seals in a normal Wankel, the housing does that job in the X1 engine. This allows significant reduction in oil consumption over a regular rotary motor.

Other enhancements include direct injection, a high compression ratio at 18:1, and a dramatic change to the geometry of the combustion chamber, which maintains a constant volume during ignition. This change means the air-fuel mixture auto-ignites like a diesel, and can be burned much longer than normal. The result is a more complete combustion ending in low emissions and very high chamber pressures. This high pressure is allowed to act on the rotor until it reaches nearly atmospheric pressures, so almost all the available energy is extracted before the exhaust is physically pushed out. Again, this is different than a normal internal combustion engine, which releases very energetic, high-pressure exhaust gas.

Some other slick features: Since the engine is designed to convert so much more heat energy into mechanical force, less heat has to be removed from the block, so there's actually no water cooling system. In cases where the engine is under load and needs to cool down, it can skip a fuel injection event and just suck in cool air, which is then heated by the block and gets exhausted. Another option is to inject water into the combustion chamber. This has three effects: cooling the engine, reducing NOx emissions, and converting some of the water to steam, which increases power.

LiquidPiston emerged in 2003, when the Shkolniks invented the high-efficiency hybrid cycle, or HEHC, a motor based on a four-stroke thermodynamic cycle. The men named the company LiquidPiston because they had initially planned to use liquid-piston technology similar to that found on the Humphrey pump. Used in large-scale water-supply projects in the early 20th century, the pump operated by compressing a mixture of flammable gas and air with a cylinder of water. But no LiquidPiston engine, including its current Mini X, has ever used an actual liquid piston.

The engine is... the fruit of a dozen-odd years of work by LiquidPiston, a startup co-founded by Alec Shkolnik, who has a Ph.D. in computer science, with a specialization in AI and modeling. The engine itself is based on combustion technology developed by his father, Nikolay, a Soviet-trained mechanical engineer who retrained in the United States as a physicist.

Its kind of a Wankel flipped inside out, a design that solves the old problems with sealing and fuel consumption, says company founder Alec Shkolnik. The Wankel has a triangular rotor inside a peanut-shaped housing; we have a peanut-shaped rotor inside a triangular housing. Our seals go at the apexes of the triangle [...] and our seals are stationary because theyre in the housing.

The seals stop gas from moving from one chamber to another. In a Wankel, the seals move rapidly, and that makes them hard to lubricate. You have to spray oil into the combustion chamber knowing that only a fraction will reach the seals and the rest will go up in smokea problem for both fuel economy and engine emissions. LiquidPistons engine lacks that baggage but retains the rotary engines intrinsic mechanical simplicityjust a rotor and an eccentric shaft, together with fuel injectors, fuel pumps and oil pumps.

The engine is more efficient than a Wankel becaues it has a higher compression ratio and because the shifting geometry of its internal cavities lets it extract most of the energy of the exhaust gases before voiding them, a feature called over-expansion.

Toyota uses the Atkinson cycle in its Prius, and that does overexpansionso its not new, he says. But the Prius engine is oversized. We get over-expansion almost for free, just by changing the location of our [valve] port. We dont have to have clunky valve trains to achieve that.

#### BEC

##### Well-Known Member
I have never driven an Rx-8 either. I didn't dare, for fear that I'd want one too badly. Never liked the looks of it, though.

I drove an Rx-2 sedan in college and well into my Boeing career (had 212K miles on it when it was rear-ended pretty badly and it was due for another rebuild - but I still miss it), and we had an Rx-4 wagon for several years as well. But it started when I talked my Dad into buying an Rx-3 wagon (rather than a Pinto wagon(!!)) while I was still in high school.

I have also driven a Cosmo coupe and a Rotary Pickup and I think I test drove an Rx-7 (first generation) once....

Still Mazda family - I have a 2013 Mazda3 hatchback myself - but as I say, I miss my rotary cars though not an average of 17 mpg in my Rx-2 and less in the Rx-4 I don't miss that much. My 3, with the Skyactive 2.0, is averaging almost double that 17 mpg and it is a kick to drive if I choose to push it.

#### Andy Greene

##### Well-Known Member
There is hope. Their latest concept car is a rotary design and it seems that there are some at Mazda that are interested in continuing the rotary tradition. I haven't driven the RX-8 but I have been able to drive all of the previous RX platforms at least once. My favorites are the 1st and 3rd gen RX-7, both are wonderfully balanced, responsive cars.
I wrote service for Mazda for 13 years and drove em all including the 8 - fun fun cars . The Gen III turbo cars where a wrenches nightmare, the under hood heat they produced made everything very brittle, including all those wonderful little vacuum lines and tees - touch one thing and open pandoras box lol. Some of the service files where the size of a large cities phone book back in the day, and any of em with an automatic ate apex seals by 25-30k . Fun times for the warranty claims lady

TRF Supporter

#### YodaMcFly

##### Finally!
TRF Supporter
I have never driven an Rx-8 either. I didn't dare, for fear that I'd want one too badly. Never liked the looks of it, though.

I drove an Rx-2 sedan in college and well into my Boeing career (had 212K miles on it when it was rear-ended pretty badly and it was due for another rebuild - but I still miss it), and we had an Rx-4 wagon for several years as well. But it started when I talked my Dad into buying an Rx-3 wagon (rather than a Pinto wagon(!!)) while I was still in high school.

I have also driven a Cosmo coupe and a Rotary Pickup and I think I test drove an Rx-7 (first generation) once....

Still Mazda family - I have a 2013 Mazda3 hatchback myself - but as I say, I miss my rotary cars though not an average of 17 mpg in my Rx-2 and less in the Rx-4 I don't miss that much. My 3, with the Skyactive 2.0, is averaging almost double that 17 mpg and it is a kick to drive if I choose to push it.

Continuing the drift: Mazda raced a rotary at Le Mans in 1990 and 1991; they won in 1991, and the rotary was subsequently banned by the FIA ...

(No, it wasn't banned because it won, although that sounds cool. There were a number of issues around the issue. Although, any way you look at it, the R26B was an awesome piece of kit ...)

#### cls

##### Well-Known Member
That is so badass. A real forehead slapper, duh why didn't I think of that!??!!

But it looks like they really put in some time for development.

#### KenECoyote

##### Well-Known Member
TRF Supporter
Funny thing is that many years ago I spent a good amount of spare time trying to design a new type of rotary engine and one of my designs came close to this one. The big problem I figured (and same with the wankel and from what I see here) is the amount of friction present in a system like this (necessary to get good compression) along with the trouble of lubrication and keeping the lubricant separate from combustion. Maybe with new metals or coatings this can work, but I don't quite see it based on my experience trying to design something like this.

FWIW I thought something like a combination turbine/rotary would be the answer...this one is almost like it in a way, but not enough IMO. I'd guess a turbo added would improve it a lot, but again heat would be a problem.

#### Viking

##### Well-Known Member
...
The Gen III turbo cars where a wrenches nightmare, the under hood heat they produced made everything very brittle, including all those wonderful little vacuum lines and tees - touch one thing and open pandoras box lol.
...
This could probably be said for many turbo'd cars that experience frequent 'spirited' driving.
I know it's the same issue for my GC8 WRX, age and heat are the big enemies for rubber. Last major service I also had to replace 3 vacuum lines and one tee after they broke while moving them for access.
One of the vacuum lines was to the wastegate and has a restrictor 'pill' that can barely be seen, just the slightest bump in the line.
Fortunately I knew it was in there or I'd have had some serious issues. Slicing it out and pushing it down into the new vac line was trivial.

#### Screaminhelo

I wrote service for Mazda for 13 years and drove em all including the 8 - fun fun cars . The Gen III turbo cars where a wrenches nightmare, the under hood heat they produced made everything very brittle, including all those wonderful little vacuum lines and tees - touch one thing and open pandoras box lol. Some of the service files where the size of a large cities phone book back in the day, and any of em with an automatic ate apex seals by 25-30k . Fun times for the warranty claims lady
My RX-7 was a secondhand 81 GSE. I was able to pull the rat's nest and get around that problem.

#### bobkrech

##### Well-Known Member
The devil is in the detail. How long will it operate without major teardown/rebuild, what is the specific fuel economy, what is the production costs, how good are the seals and how well will it meet emission standards?

I'm not impressed with the go kart demo. The 70 cc motor develops 3 hp at 10,000 rpm is not impressive. That's only 42 hp/liter which is rather underwhelming.
I found this OEM 4-stroke 50 cc motor cycle engine that develops 3 hp at 7,500 rpm. That 60 hp/liter while is more nominal, but also not that impressive. https://www.ebay.com/itm/139QMB-50C...OTOR-AUTO-CARB-LONG-CASE-V-EN28-/160865535527

Nothing is stated about the fuel economy. My old 1950 pound 1983 gas 1.5 liter Nissan Sentra with a 4 speed stick got 43 mph average mpg in the summer. My old 2050 pound 1992 Nissan Sentra 4 speed with a 1.6 L gas engine developed 110 hp (69 hp/liter) and got 39 mpg. A friend's current 2014 2L turbo-diesel Cruze gets 46 mph highway. The Mazda rotary may have had a lot of power but was not known for fuel economy or meeting emission standards, and as previously mentioned was problematic when it came to maintenance.

Seal life, engine wear, and thermal issues were problematic in all rotary engines. I'm not sure how anything is different with this version.