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Common Rail (2nd generation)

1600 bar, metering valve in the low-pressure circulation

From the year 2000 onwards, the 2nd generation system from Bosch was primarily built into the brands BMW, Mercedes and Opel. By now the injection pressure has risen to approx. 1600 bar. The three-piston-high- pressure pump had recieved a metering unit (see picture on the far left), which on the low-pressure side, limits the fuel allocation for the pump area, which increases the efficiency of the high-pressure pump. The pump now produces only as much high-pressure Diesel as the valve allocates. The rest benefits the lubrication and the pump-cooling. The pump is thus spared the full stroke under this high pressure, which reduces the power input and also the consumption. A three-piston pump of this type can take up as much as up to 5 kW (7 HP) of engine power.

No longer any fuel-cooling, the drive of the high-pressure unit more simple.

A further advantage is the now missing fuel cooler in the flow-back. This saves money in the manufacturing costs. The temperature and amount in the flow-back can be reduced through the regulating valve. The volume control valve can, depending on the manufacturer, have different names, e.g., metering valve, volume-control valve or inflow throttle. For their mounting, the majority of high-pressure pumps do not need any particular, precise position in relation to the crank- or camshaft. The vibration-, tensile and pressure strain are lower, e.g., in relation to the pump-jet. The possibility for the manufacturer to vary the size of the pump according to the cubic capacity, works positively on the efficiency. Thus, in the meantime, there are pumps with 1 - 4 pistons. The high-pressure valve on the Rail could actually be left out, however, for safety reasons, it sometimes still exists.

Higher voltage, two injections, softer combustion.

The injectors are, as in the 1st generation from Bosch, controlled by magnetic valves. This system functions with one pre- and one main injection. The pre-injection gives a softer combustion and a more gentle pressure increase in the cylinder, which improves the running culture of the Diesel engine. Instead of the 12V-on-board electrics, the injectors work with approx. 50 to 70 volts, which allows the injectors to open more abruptly. The high tension is created by condensers in the control device. The magnetic valves are then held by 12V-clocking. The injectors are provided with a tolerance-code from the manufacturers. This can be read out from the top of the injector and must be given to the control device. Apparently, individual injectors spray in varying amounts of fuel, despite the pressure- and opening phases being the same. After an exact testing directly after the production, the code is determined. Of course, only the manufacturer can do anything with the code.

Post-injection was already realised in the 2nd. generation.

Towards the end of the 2nd generation era, the after-burning in the particle-filter becomes acute. This is where the Common-Rail can play an important trump-card against, e.g., the pump-jet, since basically, any length of after-burning is possible. Before, in the 3rd generation, the multi-injection is realised, there will still be an optional injection long after TDC carried out through magnetic valves. However, since the introduction of this technology, the Diesel engine has, for the first time in its long life, to battle against fuel thinner in the engine oil. 07/10

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