The term six stroke engine describes two different approaches in the internal combustion engine, developed 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.[1] 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's 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.
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[edit] Engine types
[edit] Griffin six stroke engine
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".[2] 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. [3] [4]
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. [5]
[edit] Bajulaz six stroke engine
The Bajulaz six stroke engine is similar to a regular combustion engine in design. There are however modifications to the cylinder head, with two supplementary fixed capacity chambers: a combustion chamber and an air preheating chamber above each cylinder. The combustion chamber receives a charge of heated air from the cylinder; the injection of fuel begins an isochoric burn which increases the thermal efficiency compared to a burn in the cylinder. The high pressure achieved is then released into the cylinder to work the power or expansion stroke. Meanwhile a second chamber which blankets the combustion chamber, has its air content heated to a high degree by heat passing through the cylinder wall. This heated and pressurized air is then used to power an additional stroke of the piston.
The advantages of the engine include reduction in fuel consumption by at least 40%, two expansion strokes in six strokes, multi-fuel usage capability, and a dramatic reduction in pollution.[6]
The Bajulaz Six Stroke Engine was invented in 1989 by the Bajulaz S A company, based in Geneva, Switzerland; it has U.S. Patent 4,809,511 and U.S. Patent 4,513,568.
The Bajulaz six stroke engine features:
- Reduction in fuel consumption by at least 40%
- Two expansion (work) strokes in six strokes
- Multifuel, including liquefied petroleum gas
- Dramatic reduction in air pollution
- Costs comparable to those of a four-stroke engine
[edit] Velozeta six-stroke engine
In a Velozeta engine, during the exhaust stroke, fresh air is injected into the cylinder, which expands by heat and therefore forces the piston down for an additional stroke. The valve overlaps have been removed and the two additional strokes using air injection provide for better gas scavenging. The engine seems to show 40% reduction in fuel consumption and dramatic reduction in air pollution.[7] Its specific power is not less than that of a four-stroke petrol engine.[7] The engine can run on a variety of fuels, ranging from petrol and diesel to LPG. An altered engine shows a 65% reduction in carbon monoxide pollution when compared with the four stroke engine from which it was developed.[7]
The Velozeta engine features are:
- Reduction in fuel consumption
- Dramatic reduction in pollution
- Better scavenging and more extraction of work per cycle
- Lower working temperature makes it easy to maintain optimum engine temperature level for better performance
- The six-stroke engine does not require significant modification to existing engines.
- Better cooling due to additional air strokes, which mostly removes the need for a cooling system
- Lighter engine
This six-stroke engine was developed by the students of College of Engineering, Trivandrum in India. The Team includes Aaron George, Arun K. Nair, Boby Sebastian , Krishnaraj U. and Anil CC. The Engineering students have been awarded the 'Indian Society for Technical Education - National awarded' for Best B. Tech project of 2006. (ISTE/BBSBEC-B.Tech./Award/2006)[8] The technology is being developed by Velozeta, a Technopark (Trivandrum) supported by the National Institute of Technology based in Calicut. Velozeta has been awarded a Phase-I research grant from the Department of Scientific & Industrial Research (Govt. of India) under the Technopreneur Promotion Programme (TePP).
[edit] Crower six stroke engine
In a six-stroke engine developed in the U.S. by Bruce Crower, fresh water is injected into the cylinder after the exhaust stroke, and is quickly turned to superheated steam, which causes the water to expand to 1600 times its volume and forces the piston down for an additional stroke. [9] This design also claims to reduce fuel consumption by 40%.
The Crower six stroke engine was invented in 2004 by 75 year old American inventor Bruce Crower who has applied for a patent on a design involving fresh water injection into the cylinders. As of May 2008, no patent has been awarded. [10] ([2]) Mr. Dyer invented the first six-stroke internal combustion water injection engine in 1915, which is very similar to Crower's design. [11] Crower's six stroke engine features:
- No cooling system required
- Improves a typical engine’s fuel consumption
- Requires a supply of distilled water to act as the medium for the second power stroke.
[edit] Beare Head
The term "Six Stroke" was coined by the inventor of the Beare Head, Malcolm Beare. The technology combines a four stroke engine bottom end with an opposed piston in the cylinder head working at half the cyclical rate of the bottom piston. Functionaly, the second piston replaces the valve mechanism of a conventional engine.
[edit] Charge pump engine
In this engine, similar in design to the Beare head, a "piston charger" replaces the valve system. The piston charger charges the main cylinder and simultaneously regulates the inlet and the outlet aperture leading to no loss of air and fuel in the exhaust.[12] In the main cylinder, combustion takes place every turn as in a two-stroke engine and lubrication as in a four-stroke engine. Fuel injection can take place in the piston charger, in the gas transfer channel or in the combustion chamber. It is also possible to charge two working cylinders with one piston charger. The combination of compact design for the combustion chamber together with no loss of air and fuel is claimed to give the engine more torque, more power and better fuel consumption. The benefit of less moving parts and design is claimed to lead to lower manufacturing costs.Good for hybrid technology and stationary engines. The engine is claimed to be suited to alternative fuels since there is no corrosion or deposits left on valves. The six strokes are: aspiration, precompression, gas transfer, compression, ignition and ejection.
[edit] Related U.S. Patents
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
