Double acting internal combustion engine
A double-acting internal combustion engine is an engine that has a combustion chamber both above and below the piston , i.e. two combustion chambers per cylinder .
Working principle
The cylinder is closed both at the top and at the bottom by a cylinder cover, creating two combustion chambers that are separated from one another by the piston. A piston rod is firmly attached to the piston and is guided through the lower cylinder cover in a gas-tight manner. Under the lower cover, the piston rod is connected to a connecting rod via a cross head , through which the power is passed on to the crankshaft .
The double-acting principle is theoretically possible with all combustion engines, i.e. Otto - like diesel engines , two - and four-stroke engines . However, only two- and four-stroke diesel engines were actually built; attempts with gasoline engines were unsuccessful. Two-stroke engines had external scavenging fans because the crankcase could not be used as a scavenging pump.
Double-acting cylinders are common and proven in steam engines . So have steam locomotives almost continuously over this. By adopting the principle, an attempt was made to increase the power density of an engine. A double-acting four-stroke engine theoretically achieves the performance of a single-acting two-stroke engine. In practice, there is a loss of power because the piston rod makes the lower combustion chamber smaller and fissured. In addition, the power output is more uneven because the work cycles between the upper and lower combustion chambers are offset by 180 ° crank angle to one another. The ignition interval in the double-acting four-stroke cylinder is 180 ° / 540 °. A double-acting two-stroke engine has no uneven power output, the ignition interval is 180 ° / 180 °.
history
The development and construction of double-acting four-stroke engines was given up in the 1930s. The construction of double-acting two-stroke engines for stationary applications and ship propulsion ended in the mid-1950s. The best known double-acting two-stroke engines include the two-stroke cross-head in-line engine MAN DZ 53/800 with a cylinder output of 596 kW at 214 rpm and the 24-cylinder V-engine MAN V24Z 32/44 developed for the German Navy .
With the use of exhaust gas turbochargers , the power density of single-acting engines could be increased in a structurally lighter, more effective and operationally reliable manner, which led to the end of double-acting engines.
disadvantage
The disadvantages of double-acting motors include:
- High thermal load on the piston, which is heated from above and below by the combustion, but can only poorly dissipate the heat via the piston rings and cylinder wall.
- Elaborate piston construction, as the combustion pressure has to be withstood in both directions. As a result, expensive, complex and heavy piston constructions and high oscillating masses.
- In the lower combustion chamber, no central injection or ignition is possible due to the piston rod, and the combustion chamber is also fissured by the piston rod. Both have a detrimental effect on the mixture formation and combustion .
- The sealing of the piston rod in the lower combustion chamber cover is very prone to failure and poorly suited for higher combustion pressures. The use of heavy oil exacerbates the sealing problem.
literature
- Richard van Basshuysen (Hrsg.): Lexicon engine technology . 2nd Edition. Vieweg-Verlag, Wiesbaden 2006, ISBN 3-528-13903-X .