Swirl chamber injection

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Principle sketch of the vortex chamber injection

The swirl chamber injection was until the 1990s, widespread injection principle for diesel engines ( chamber diesel engine ). It was developed by Harry Ricardo in 1931 . Today it has largely been supplanted by direct injection and is only used if a direct injection system would mean a disproportionate effort in relation to the requirements ( emergency power generators , lawn tractors , micro-cars, small boats, etc.).

description

Diesel engines that work according to the swirl chamber process have a swirl chamber in the shape of a ball or cylinder, which is connected to the main combustion chamber via a tangentially opening channel (firing channel) . As with other chamber diesel engines, the fuel is injected indirectly into the combustion chamber, in contrast to direct injection .

During compression, air from the main combustion chamber is pressed through the firing channel into the swirl chamber and, due to the tangential opening of the firing channel, is set in strong rotation (air vortex). The fuel is now injected into the swirl chamber in the direction of the air movement. The centrifugal effect creates a mixture stratification with a rich mixture on the periphery of the chamber, but hardly any fuel accumulates on the chamber walls. This results in a good fuel- air mixture.

When combustion begins, the rich mixture is pressed through the firing channel into the main combustion chamber, where it mixes with the rest of the air and burns completely. Mixing is supported by suitable shaping of the top of the piston for air swirling.

Advantages and disadvantages

Compared to the pre-chamber process , the flow losses are lower and the efficiency is higher. In addition, the turbulence improves the mixing and thus the combustion, which, together with the larger firing channel area, enables adequate power , torque and efficiency even at higher speeds (over 5000 min −1 ) . In contrast to the prechamber, the swirl chamber does not have an impact pin, but rather the fuel is partially injected onto the swirl chamber wall opposite the injection nozzle . The operating temperature of the wall is sufficiently high that the fuel evaporates quickly here too, and it is carried away by the air vortex. The good mixing of the fuel with the combustion air is also achieved by the spherical design of the swirl chamber, which ensures particularly high flow speeds.

The spherical shape means that the swirl chamber heats up more quickly after a cold start . This allows the ignition delay to be reduced, which is noticeable in a good exhaust gas behavior even without aids.

The swirl chamber injection produces a very soft combustion, the engine runs comparatively quietly. In the 1990s, some car manufacturers stuck to vortex chamber technology for a relatively long time, because at that time it represented the best compromise in terms of noise, exhaust emissions and consumption and it would have incurred disproportionate costs to adapt a direct injection engine in this regard.

The combustion process makes the swirl chamber principle suitable for a wide variety of fuels. Therefore, multi-fuel engines are often designed as vortex or pre-chamber engines .

The disadvantage of this two-stage combustion is the large cooling surface of the vortex chamber, which quickly cools the compressed air. For this reason, such engines do not start even when they are warm without additional chamber heaters; glow plugs for swirl chamber heating are common for cold starts , and their failure can only be compensated for by towing the vehicle. Even more serious, especially for larger trucks, are the flow losses, which at higher speeds increase consumption by up to 30% compared to direct injection and reduce torque by approximately the same percentage. However, swirl chamber motors reach their maximum performance at higher speeds, so that the performance disadvantage is only approx. 16%.

The large surface area of ​​the swirl chamber and the flow losses due to the division of the combustion chamber have a negative effect on consumption, which, depending on the speed and load, can be 5–30% higher than with a comparable diesel engine with direct injection.

Exhaust emissions

The exhaust gas behavior of the vortex chamber injection depends on the combustion air ratio . From a combustion air ratio of about are hydrocarbon - and nitrogen oxide emissions at its lowest. The carbon monoxide emissions are negligibly low due to the diesel principle. Other exhaust gas components are water, oxygen, nitrogen and C 2 .

literature

swell

  1. ↑ Heinz Grohe: Otto and diesel engines . Vogel-Verlag Würzburg, ISBN 3-8023-1559-6
  2. ^ Otto Kraemer , Georg Jungbluth : Construction and calculation of internal combustion engines . Springer publishing house. Berlin, Heidelberg. 1983. ISBN 9783642932410 . Pp. 65 and 66.

See also