''' The M4+2 engine''', also known as the double-piston internal [[combustion]] engine, is a type of [[internal combustion engine]] invented by Polish patent holder Piotr Mężyk.<ref name="Piotr Mężyk">[http://izoling.beep.pl/www.izoling.pl/badania/czytaj/engine.html Double pistons internal combustion engine], Official site of the city of [[Myszków]], Poland. {{in lang|pl}} {{webarchive |url=https://web.archive.org/web/20170109041809/http://izoling.beep.pl/www.izoling.pl/badania/czytaj/engine.html |date=2017-01-09}}</ref>
The M4+2 engine took its name from a combination of [[two-stroke engine]]s and [[four-stroke engine]]s. The two-stroke combustion engine is characterized by a simple construction and system of air load change, as well as a bigger index of power output. UnfortunatelyHowever, its filling ratio is worse than in a four-stroke engine. The ecological index of a two-stroke engine is also unfavorable. The system of valves of the four-stroke engine is its disadvantage. The cylinders of both modules of the double-pistons engine have been joined along one axis with a common cylinder head – in the form of a ring. The pistons are moved at different speeds and with appropriate stage displacement. The two crankshafts are connected with a special transmission that rotates the four-stroke crankshaft at twice the speed of the two stroke crankshaft. The engine is named double-piston because of its construction – double pistons and crankshafts. In the M4+2, the advantages of both engines being connected are obvious; the [[piston]]s of the engine working in one [[combustion]] [[Cylinder (engine)|cylinder]] are set opposite to each other but in different modes. Although the projects of connecting two-stroke modes in one cylinder were attempted a long time ago in the [[opposed-piston engine]], the combination of the two different cycles had never been tried before. It turned out that the engine is not only able to work but also the effects are very promising. The engine has a far greater efficiency over the break-even value known to combustion engines (about 35%) and closer to the one associated with [[steam turbines]] or [[electric engines]] (about 70%).{{Citation needed|reason=this should be in one of the already cited refs|date=April 2010}}
[[File:proto.jpg|thumb|200px|The M4+2 [[prototype]] constructed at the [[Silesian University of Technology]], [[Poland]]]]
The otherOther advantages are:
* More efficient [[power (physics)|power]] production (150 [[horsepower]] from 1000 cc of volume in the basic version)
* Ability to use different [[fuel]] types (natural plant oils as well as petroleum)
