1.0 TD engine swirl chamber. On the right is the vortex chamber under magnification. The arrows show the swirl of air in the chamber, which is thus mixed with the injected fuel.
1 - nozzle
2 - glow plug
3 - vortex chamber
4 - cut-off channel
5 - piston
With TDI engines, fuel is injected directly into the main combustion chamber, namely into the combustion channel in the piston. In order to ensure good combustion of the mixture, the air must first be swirled. For this reason, the air on its way to the combustion chamber swirls in the spiral intake ducts (see illustrations 1.0a).
The high-performance distributor injection pump generates injection pressures up to 900 bar. This allows short injection times to be achieved. The high pressure also ensures a high degree of atomization of the diesel fuel. This is facilitated by the new design of fuel injectors, which have five holes with a diameter of 0.21 mm.
The advantage of direct injection is lower fuel consumption. The disadvantage of this method is the increased noise of the engine. To eliminate this disadvantage, pre-injection in multi-jet sprayers is carried out using a nozzle with a double spring valve (see illustration 1.0b).
This injector performs fuel injection in two stages. When making the first move (rise) valve, a small amount of fuel is pre-injected. This fuel provides improved conditions for igniting the main quantity that is injected during the second valve lift.
The injector valve is held by two springs, acting in such a way that during the preliminary injection of fuel, the resistance of only one spring is overcome and the injector opens by 0.06 mm. At the end of the pre-injection, a higher pressure is created in the injector, due to the need to inject more fuel. As a result of the increased pressure, the resistance of the second spring is overcome and the valve performs a second lift.
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