Single-piston designs These designs use a single piston per cylinder, like a conventional two- or four-stroke engine. A secondary, nondetonating fluid is injected into the chamber, and the leftover heat from combustion causes it to expand for a second power stroke followed by a second exhaust stroke.
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". 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 did not 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 a heated, exhaust-jacketed external vapouriser, into which the fuel was sprayed. The temperature was held around , 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 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.
Dyer six-stroke engine Leonard Dyer invented a six-stroke, internal combustion, water-injection engine in 1915, very similar to Crower's design (see below). A dozen more similar patents have been issued since. Dyer's six-stroke engine features: • No cooling system required • Improves a typical engine's fuel consumption • Requires a supply of pure water to act as the medium for the second power stroke. • Extracts the additional power from the expansion of steam.
Bajulaz six-stroke engine The Bajulaz six-stroke engine is similar to a regular combustion engine in design, but modifications were made 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 (constant-volume) 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 claimed advantages of the engine include reduction in fuel consumption by at least 40%, two expansion strokes in six strokes, multiple-fuel usage capability, and a dramatic reduction in
pollution. The Bajulaz six-stroke engine was invented in 1989 by Roger Bajulaz of the Bajulaz S.A. company, based in
Geneva,
Switzerland; it has and . The Bajulaz six-stroke engine features claimed are: • 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
Velozeta six-stroke engine In a Velozeta engine, fresh air is injected into the cylinder during the exhaust stroke, 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. Its
power-to-weight ratio is slightly less than that of a four-stroke gasoline engine. The name of the engine is taken from the name of his company, NIYKADO Motors. The engine underwent a preliminary round of full-throttle tests at the Automotive Research Association of India, Pune.
Porsche six-stroke engine Opposed-piston designs These designs use two pistons per cylinder operating at different rates, with combustion occurring between the pistons.
Beare head The design of the
Beare-head engine was developed by Malcolm Beare of
Australia. 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. Functionally, the second piston replaces the valve mechanism of a conventional engine. Claimed benefits include a 9% increase in power, and improved thermodynamic efficiency through an increased compression ratio enabled by the elimination of the hot exhaust valve. The working principle of the engine is explained in the
two- and four-stroke engines article.
Other two-piston designs Piston-charger 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. In the main cylinder, combustion takes place every turn as in a
two-stroke engine, while lubrication is achieved in the same manner as in a
four-stroke. 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 efficiency. The benefit of fewer moving parts and design is claimed to lead to lower manufacturing costs. The engine is claimed to be suited to alternative fuels since no corrosion or deposits are left on valves. The six strokes are: • Aspiration • Precompression • Gas transfer • Compression • Ignition • Ejection. This is an invention of Helmut Kottmann from Germany, while working 25 years at MAHLE GmbH piston and cylinder construction. Kottman's US patents 3921608 and 5755191 are listed below.
Ilmor/Schmitz five-stroke This design was invented by Belgian engineer Gerhard Schmitz, and has been prototyped by Ilmor Engineering. These designs use two (or four, six, or eight) cylinders with a conventional Otto four-stroke cycle. An additional piston (in its own cylinder) is shared by the two Otto-cycle cylinders. The exhaust from the Otto-cycle cylinder is directed into the shared cylinder, where it is expanded, generating additional work. This is in some respects similar to the operation of a compound steam engine, with the Otto-cycle cylinders being the high-pressure stage and the shared cylinder the low-pressure stage. The operation of the engine is: The designers consider this to be a
five-stroke design, regarding the simultaneous HP exhaust stroke and LP expansion stroke as a single stroke. This design provides higher fuel efficiency due to the higher overall expansion ratio of the combined cylinders. Expansion ratios comparable to diesel engines can be achieved, while still using gasoline (petrol) fuel. Five-stroke engines allegedly are lighter and have higher power density than diesel engines.
Revetec engines The
controlled combustion engines, designed by Bradley Howell-Smith of Australian firm Revetec Holdings Pty Ltd, use opposed pairs of pistons to drive a pair of counter-rotating, three-lobed cams through bearings. These elements replace the conventional crankshaft and connecting rods, which enable the motion of the pistons to be purely axial, so that most of the power otherwise wasted on lateral motion of the con rods is effectively transferred to the output shaft. This gives six power strokes per revolution of the shaft (spread across a pair of pistons). An independent test measured the
brake specific fuel consumption of Revetec's X4v2 prototype gasoline engine at 212g/kW-h (corresponding to an energy efficiency of 38.6%). Any even number of pistons can be used, in boxer or X configurations; the three lobes of the cams can be replaced by any other odd number greater than one; and the geometry of the cams can be changed to suit the needs of the target fuels and applications of the engines. Such variants may have 10 or more strokes per cycle. ==Related patents==