Reverse flush

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Two-stroke engine with reverse scavenging

The reverse circulation is a method of gas exchange in the cylinder of a two-stroke engine . The piston controls the inlet and outlet openings for the gas exchange process, all three openings are arranged next to one another in the cylinder wall instead of opposite one another as in the older cross-flow flushing . When Schnürle purge it three channels are involved, two fresh gas channels and an exhaust duct . The patent was in 1925 by Klockner-Humboldt-Deutz for two-stroke diesel engines submitted.

In 1932 DKW acquired a license for reverse scavenging on gasoline engines , and from 1934 all DKW models were equipped with it. The engines were developed and mass-produced under the direction of Herbert Josef Venediger .

Technical process

The fresh gases are first pre-compressed in the crankcase . The exhaust gas duct opens shortly before the fresh gas ducts open. The escaping residual gases create a negative pressure in the combustion chamber , which promotes purging. The fresh gases then enter the cylinder through the two fresh gas ducts located to the right and left of the exhaust duct. There they are directed to the cylinder wall opposite the exhaust gas duct and deflected there upwards and finally in the direction of the exhaust duct (hence “reverse” flushing). In this way they push the burned residual gas out of the cylinder. Fresh gas and exhaust gas only mix slightly in this process. Here are scavenging losses , the previous methods such as the cross-flow flushing with a nose piston adhered greatly reduced.

However, pure reverse scavenging still has higher scavenging losses than newer methods, which is why many manufacturers of two-stroke engines combine the technology with a scavenging air reservoir . The specific consumption is reduced and the efficiency of the engine is increased. Newer engines work with four transfer ducts, one duct leading out of the crankcase pump, which is first divided into two and then each into two more. With this technology, two different angles of fire for the fresh gas into the work area can be achieved.

This procedure has been further refined. There were various approaches to circumventing DKW's patents, which in some cases also succeeded. Support overflow channels have been integrated to improve the purging process and also avoid the formation of exhaust gas cores in the combustion chamber; In some designs, the flows through the piston interior are guided through piston windows. In the vehicle sector, reverse flushing is the most widespread method for flushing two-stroke engines today; it is used almost exclusively in hand-held power tools (e.g. chainsaws ) and frequently used in glow-igniter engines in model construction.

Criticism of the granting of a patent in favor of Schnürle

The motor journalist Siegfried Rauch writes: “In 1924, 1925 and 1931 Adolf Schnürle had received patents on reverse flushing systems that worked with flat piston. It is incomprehensible that he received these patents. Because long before that there were other patents that not only looked astonishingly similar to the Schnürle proposals, but were occasionally even congruent with them. ”This means that the Reich patent no. DE207107“ Order of Insertion slots on internal combustion engines ”and the patent no. DE241448“ Arrangement of scavenging slots on internal combustion engines ”granted to Arnold Freiherr von Schmidt on February 17, 1911.

In 1919, attempts at MAN began with reverse flushing, and in 1923 the first MAN engine with this system was developed for series production. The system was used at MAN until the early 1980s.

literature

  • Helmut Werner Bönsch: The high-speed two-stroke engine . Motorbuch Verlag, Stuttgart 1982, ISBN 3-87943-800-5 .
  • Herbert J. Venediger: Two-stroke flush, in particular reverse flush. (= Books of the MTZ, Volume 1) Franckh, Stuttgart 1947
  • Heinz Britsch: Characterization of the reverse scavenging process on the slot-controlled two-stroke gasoline engine. Dissertation, Freiberg, Bergakademie, 2010
  • Matthias Boltze: Gas exchange calculation on the two-stroke engine. Dissertation Dresden, Technical University, 1995
  • Wolf Albrecht Doernhoeffer: Two-stroke internship . Franckh-Kosmos, Stuttgart 1942. Reprinted under the title Zweiakt -Praxis Rieck, Eschborn 1995. ISBN 3-924043-19-1
  • Tim Gegg: Analysis and optimization of the mixture formation and the exhaust emissions of small-volume two-stroke gasoline engines (= research reports from the Institute for Piston Engines of the University of Karlsruhe, Volume 2007.1) Dissertation, Karlsruhe, University, 2007. Logos-Verlag, Berlin 2007. ISBN 978- 3-8325-1723-6 .

Individual evidence

  1. ^ Christian Bartsch (ed.): A century of motorcycle technology . VDI-Verlag, Düsseldorf 1987, ISBN 3-18-400757-X , p. 149 .
  2. ^ Günter Mau: Handbook Diesel Engines in Power Plant and Ship Operation, Vieweg (Springer), Braunschweig / Wiesbaden 1984, ISBN 978-3-528-14889-8 . P. 12
  3. ^ Günter Mau: Handbook Diesel Engines in Power Plant and Ship Operation, Vieweg (Springer), Braunschweig / Wiesbaden 1984, ISBN 978-3-528-14889-8 . P. 16