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Shamelessly copied from Wikipedia

Five-stroke
The British company ILMOR presented a prototype of 5-Stroke double expansion engine, having two outer cylinders, working as usual, plus a central one, larger in diameter, that performs the double expansion of exhaust gas from the other cylinders, with an increased efficiency in the gas energy use, and an improved SFC. This engine corresponds to a 2003 US patent by Gerhard Schmitz, and was developed apparently also by Honda of Japan for a Quad engine. This engine has a similar precedent in a Spanish 1942 patent (# P0156621 ), by Francisco Jimeno-Cataneo, and a 1975 patent (# P0433850 ) by Carlos Ubierna-Laciana ( Oficina Española de Patentes y Marcas - Inicio ). The concept of double expansion was developed early in the history of ICE by Otto himself, in 1879, and a Connecticut (USA) based company, EHV, built in 1906 some engines and cars with this principle, that didn't give the expected results
 

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Five-stroke
The British company ILMOR presented a prototype of 5-Stroke double expansion engine, having two outer cylinders, working as usual, plus a central one, larger in diameter, that performs the double expansion of exhaust gas from the other cylinders, with an increased efficiency in the gas energy use, and an improved SFC. This engine corresponds to a 2003 US patent by Gerhard Schmitz, and was developed apparently also by Honda of Japan for a Quad engine. This engine has a similar precedent in a Spanish 1942 patent (# P0156621 ), by Francisco Jimeno-Cataneo, and a 1975 patent (# P0433850 ) by Carlos Ubierna-Laciana ( Oficina Española de Patentes y Marcas - Inicio ). The concept of double expansion was developed early in the history of ICE by Otto himself, in 1879, and a Connecticut (USA) based company, EHV, built in 1906 some engines and cars with this principle, that didn't give the expected results
Here's a cool video showing the concept in motion:

How do they define a single cylinder 5 stroke? Does that mean it has two pistons regardless? Weird..
 

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What were you doing on North Korea's website? :p
Considering the insane nature of North Korea propaganda it's surprising those vehicles don't put out 200hp and give you 300mpg and are sweeping clean the GP series.
For a good laugh check out their cars: http://www.korea-dpr.com/business/DPRK-cars.pdf
Consider the North Korean government is one of the largest and best Mercedes-Benz customer, often paying a huge premium for early deliveries... :rolleyes:
In fact screw that, here's the page with all their marvelous exports: Business in DPR Korea
My favorite is the animation one: if you are a long time Simpson fan you may remember they poked fun at the "Itchy and Scratchy Korean studios". :D
 

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basically they use spent exhaust gasses to pressurize another cylinder that is not fired by spark, but works more like a lean burn deisle in some cases. some are just unfired all together. pretty cool idea in theory. I've heard that they have a lot of problems with the secondary "expansion cylinder" needing overhaul quite often due to carbon buildup.
 

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chimp on my shoulder
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yes and no. if you want to think about it like that it's fair, but in the strictest sense of the term" super charger" it is not. because a super charger forces a more dense (super) air fuel charge into the combustion chamber. this setup basically uses the exhaust pressure to power another cylinder. it's more like a super discharger.
 

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A two-stroke would an even better platform for this IMO as the gases are much earlier in their expansion phase when they leave the combusion chamber than is the case in a four-stroke. This should, at a glance, make the two-stroke fed intermediate cylinder more efficient. However, given the fact that the two-str fires on every revolution, the ratio of "slave" cylinders would have to be 1:1 instead of 2:1....
 
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