The term six stroke engine describes two different approaches in the internal combustion engine, which has had some developement since the 1990s, to improve its efficiency and reduce emissions:
In the first approach, the engine captures the waste heat from the four stroke Otto cycle or Diesel cycle and uses it to power an additional power and exhaust stroke of the piston in the same cylinder. Designs either use steam or air as the working fluid for the additional power stroke. As well as extracting power, the additional stroke cools the engine and removes the need for a cooling system making the engine lighter and giving 40% increased efficiency over the normal Otto cycle or Diesel cycle. The pistons in this six stroke engine, go up and down six times for each injection of fuel. These six stroke engines have 2 power strokes: one by fuel, one by steam or air. The currently notable six stroke engine designs in this class are the Crower six stroke engine, invented by Bruce Crower of the U.S. ; the Bajulaz engine by the Bajulaz S A company, of Switzerland; and the Velozeta Six-stroke engine built by the College of Engineering, at Trivandrum in India.
The second approach to the six stroke engine, uses a second opposed piston in each cylinder which moves at half the cyclical rate of the main piston, thus giving six piston movements per cycle. Functionaly, the second piston replaces the valve mechanism of a conventional engine but also increases the compression ratio. The currently notable six stroke engine designs in this class include two designs developed independently: the Beare Head engine, invented by Australian Malcolm Beare, and the German Charge pump, invented by Helmut Kottmann.
- Main article: Wikipedia:Six stroke engine for full article
Griffin six stroke engineEdit
In 1883, the Bath-based engineer Samuel Griffin was an established maker of steam and gas engines. He wished to produce an internal combustion engine, but without paying the licensing costs of the Otto patents. His solution was to develop a 'Patent slide valve' and a single-acting six-stroke engine using it.
By 1886, Scottish steam locomotive maker Dick, Kerr & Co. saw a future in large oil engines and licensed the Griffin patents. These were double acting, tandem engines and sold under the name "Kilmarnock". A major market for the Griffin engine was in electricity generation, where they developed a reputation for happily running light for long periods, then suddenly being able to take up a large demand for power. Their large heavy construction didn't suit them to mobile use, but they were capable of burning heavier and cheaper grades of oil.
The key principle of the "Griffin Simplex" was an heated exhaust-jacketed external vapouriser, into which the fuel was sprayed. The temperature was held around 550 °F (288 °C), sufficient to physically vapourise the oil but not to break it down chemically. This fractional distillation supported the use of heavy oil fuels, the unusable tars and asphalts separating out in the vapouriser.
Hot bulb ignition was used, which Griffin termed the 'Catathermic Igniter' , a small isolated cavity connected to the combustion chamber. The spray injector had an adjustable inner nozzle for the air supply, surrounded by an annular casing for the oil, both oil and air entering at 20 lbs sq in. pressure, and being regulated by a governor.  
Griffin went out of business in 1923.
Only two known examples of a Griffin six-stroke engine survive. One is in the Anson engine museum. The other was built in 1885 and for some years was in the Birmingham Museum of Science and Technology, but in 2007 it returned to Bath and the Museum of Bath at Work. 
The six strokes are: aspiration, precompression, gas transfer, compression, ignition and ejection.
Related U.S. PatentsEdit
- 1217788 Internal combustion and steam engine Feb 27, 1917. Hugo F. Liedtke seems to be one of the first to contemplate alternating between internal combustion and steam injection into the combustion chamber.
- 1339176 Internal combustion engine May 4, 1920. Leonard H. Dyer invented the first 6-stroke internal combustion/water-injection engine in 1915.
- 3964263 Six cycle combustion and fluid vaporization engine Jun 22, 1976
- 4143518 Internal combustion and steam engine Mar 13, 1979
- 4301655 Combination internal combustion and steam engine Nov 24, 1981
- 4433548 Combination internal combustion and steam engine Feb 28, 1984
- 4489558 Compound internal combustion engine and method for its use Dec 25, 1984
- 4489560 Compound internal combustion engine and method for its use Dec 25, 1984
- 4736715 Engine with a six-stroke cycle, variable compression ratio, and constant stroke Apr 12, 1988
- 4917054 Six-stroke internal combustion engine Apr 17, 1990
- 4924823 Six stroke internal combustion engine May 15, 1990
- 6253745 Multiple stroke engine having fuel and vapor charges Jul 3, 2001
- 6311651 Computer controlled six stroke internal combustion engine and its method of operation Nov 6, 2001
- 6571749 Computer controlled six stroke cycle internal combustion engine and its method of operation Jun 3, 2003
- 7021272 Computer controlled multi-stroke cycle power generating assembly and method of operation Apr 4, 2006
- ↑ "Inside Bruce Crower’s Six-Stroke Engine". www.autoweek.com (2006-12-26). Retrieved on 2007-05-25.
- ↑ "American Griffin Engine". Smokstak.com (Nov 2007)., linked photos and period diagrams
- ↑ "Griffin Engineering Company of Bath".
- ↑ Knight, Patrick. A to Z of British Stationary Engines, p. 83.
- ↑ "Only surviving Griffin engine returns home to Bath museum" (12/04/2007).
- Bajulaz Six-Stroke Engine Accessed June 2007
- Bajulaz Animation Accessed June 2007
- Six stroke engine
- Trivandru Six-Stroke Engine, Accessed June 2007
- CET students kickstart a six-stroke engine NewIndPress , September 4 2006 . Accessed June 2007
- CET students kickstart a six-stroke engine (NewIndPress; Sept. 4, 2006) [free registration required]
- Article in Mathrubhumi Newspaper (Mathrubhumi Online; Sept. 13, 2006) [Language : Malayalam]
- Revving up with love (The Hindu; Feb. 14, 2005)
- The Six-Stroke Engine (Damn Interesting; March 18th, 2006)
- Lyons, Pete (February 23, 2006). "Inside Bruce Crower’s Six-Stroke Engine", AutoWeek. Retrieved on 2007-06-22.
- College of Engineering, Trivandrum - home to a team of mechanical engineering students who have developed a six-stroke engine.
-  Mal Beare's Six-stroke head webpage.
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