Pre-chamber injection

Basic sketch of the prechamber injection

The pre-chamber injection was an injection principle for diesel engines ( chamber diesel engine ) that was widespread until the 1990s . It is characterized by the fact that the combustion chamber is divided into a main combustion chamber and an antechamber , and the fuel is injected into the antechamber. Today it has largely been supplanted by direct injection and is only used in niche applications such as B. smaller diesel generators are used.

history

The first diesel engines had air injection and only worked with the support of a compressor , as the fuel was blown into the combustion chamber with compressed air. As a result, the motors were big, heavy and hardly usable for mobile applications. Prosper L'Orange , at that time a development partner of Rudolf Diesel , invented the pre-chamber principle in 1909 , which made it possible to dispense with compressors. He laid the foundation for small, fast-running and thus for land motor vehicles suitable diesel engines.

In the prechamber diesel engine from Prosper L'Orange, the fuel is fed into an intermediate channel between the combustion chamber and the prechamber by a mechanical pump without a spray nozzle and at moderate pressure at the beginning of the compression stroke. The air compressed by the piston, which swirls from the combustion chamber into the antechamber, ensures atomization. Part of the atomized fuel ignites in the prechamber, the expansion pushes and atomizes the remaining fuel contained in the intermediate duct into the combustion chamber, where the main combustion then takes place.

The injection pump was initially a mechanical, unregulated pump, which made it difficult to influence the atomization and combustion process. An important further development was the introduction of the injection nozzle, with which fuel atomization can be carried out more precisely and in a more controlled manner.

description

In the prechamber, the size of which corresponds to about 35% of the main combustion chamber, fuel is injected with a single-hole nozzle as far as possible in the direction of the opening to the main combustion chamber. The injection pressure is comparatively moderate with a maximum of 400 bar, which has a favorable effect on the durability of the injection pump and injection valve and the use of different fuels. The shape of the prechamber should achieve a good fuel - air mixture. This is often also achieved with an impact pin (sometimes also with impact ball) arranged in the antechamber, which is hit by the injection jet. The impact pin gets very hot during operation, which means that the sprayed fuel evaporates very quickly. The ignition delay is further reduced, which makes engine speeds of 5,500 rpm and above possible.

The fuel is premixed with part of the combustion air and partly burns in the antechamber. The resulting expansion pushes the mixture through an opening channel, the so-called firing channel, into the main combustion chamber . With its pre-combustion, the prechamber thus acts like a second injection nozzle. Most of the combustion that acts on the piston takes place in the main room . Due to the low injection pressure and the controlled combustion, the load on the components is low, which, together with the low piston speeds, allows high mileage of the diesel engines (e.g. Mercedes-Benz OM 615 ).

Advantages and disadvantages

Advantages over direct injection diesel engines:

Low injection pressures from 118… 132 bar
Low ignition pressures, therefore less mechanical stress on the engine
Lower ignition delay of the subdivided combustion chamber, therefore suitable for low-boiling fuels with low ignitability ( multi-fuel properties )
Lower noise emissions compared to mechanically controlled direct injection (= without multiple injection )
Lower nitrogen oxide emissions

Disadvantages compared to direct injection diesel engines:

Common rail engines with multiple injection show better noise emission behavior.
Large heat and flow losses in the divided combustion chamber with relatively large surfaces, as a result
- poor efficiency with about 15% to 20% higher fuel consumption
- Cold starting requires glow plugs to heat the prechamber so that the auto-ignition temperature is reached
Tendency to soot (exhaust gas opacity), especially if the prechamber is cooled down while idling and then started up.

variants

Initially, diesel engines could be built compactly using the pre-chamber method, but they were still not suitable for driving vehicles. It was only with the invention of the needle injection nozzle and the funnel antechamber in 1919 and the controllable injection pump in 1921 that antechamber machines could be built capable of running at high speeds so that they could be used as vehicle drives. In the following years, primarily the shape of the antechamber was further developed in order to further reduce the ignition delay.

Some authors also refer to the M process as a special variant of the antechamber process.

literature

Richard van Basshuysen , Fred Schäfer: Handbook internal combustion engine. Basics, components, systems, perspectives. 3rd completely revised and expanded edition. Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2005, ISBN 3-528-23933-6 .
Heinz Grohe: Otto and diesel engines. Function, structure and calculation of two-stroke and four-stroke combustion engines. 11th edition. Vogel-Verlag, Würzburg 1995, ISBN 3-8023-1559-6 .

swell

^ Uwe Todsen: Internal combustion engines , 2nd edition, Carl Hanser, Munich, 2017. ISBN 978-3-446-45227-5 . P. 96
↑ Heinz Grohe: Otto and diesel engines. Function, structure and calculation of two-stroke and four-stroke combustion engines. 11th edition. Vogel-Verlag, Würzburg 1995, ISBN 3-8023-1559-6 .
↑ F. Sass, Ch. Bouché, A Leitner (ed.): Dubbels Taschenbuch für den Maschinenbau , 12th edition, Springer, Berlin / Heidelberg, 1963. ISBN 978-3-662-41645-7 . P. 177
↑ ^a ^b ^c ^d ^e ^f Rüdiger Teichmann, Günter P. Merker (ed.): Fundamentals of internal combustion engines: Functionality, simulation, measurement technology , 7th edition, Springer, Wiesbaden, 2014. ISBN 978-3-658-03195-4 . P. 381 ff.
↑ ^a ^b ^c Hans-Hermann Braess, Ulrich Seiffert (ed.): Vieweg Handbook Motor Vehicle Technology , 7th edition, Springer, Wiesbaden, 2013. ISBN 978-3-658-01691-3 . P. 310 ff.
↑ Konrad Reif: Fundamentals of vehicle and engine technology , Springer, Wiesbaden, 2017. ISBN 978-3-658-12636-0 . P. 13

[Todsen-1] Uwe Todsen: Internal combustion engines , 2nd edition, Carl Hanser, Munich, 2017. ISBN 978-3-446-45227-5 . P. 96

[Grohe-2] Heinz Grohe: Otto and diesel engines. Function, structure and calculation of two-stroke and four-stroke combustion engines. 11th edition. Vogel-Verlag, Würzburg 1995, ISBN 3-8023-1559-6 .

[Dubbel-3] F. Sass, Ch. Bouché, A Leitner (ed.): Dubbels Taschenbuch für den Maschinenbau , 12th edition, Springer, Berlin / Heidelberg, 1963. ISBN 978-3-662-41645-7 . P. 177

[Teichmann-4] ↑ ^a ^b ^c ^d ^e ^f Rüdiger Teichmann, Günter P. Merker (ed.): Fundamentals of internal combustion engines: Functionality, simulation, measurement technology , 7th edition, Springer, Wiesbaden, 2014. ISBN 978-3-658-03195-4 . P. 381 ff.

[HKT-5] Hans-Hermann Braess, Ulrich Seiffert (ed.): Vieweg Handbook Motor Vehicle Technology , 7th edition, Springer, Wiesbaden, 2013. ISBN 978-3-658-01691-3 . P. 310 ff.

[Reif-6] Konrad Reif: Fundamentals of vehicle and engine technology , Springer, Wiesbaden, 2017. ISBN 978-3-658-12636-0 . P. 13