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Diesel injection 2012
Previously, when this subject was brought up, one always spoke of a new generation of plunger-type pumps, strictly divided into the motor car- and the truck type. Nowadays they almost all fall under the category of
Common Rail. Bosch in fact, states that have delivered 2,3 million Common Rail systems to the utility vehicle sector in 2011. It is however, not enough to deal with the purely motoric aspect of the injection. At the latest,
since the appearance of Bio-Diesel, and also the exporting of vehicles to countries that have a known problem as far as fuel quality is concerned, a sensor has been added, which measures the quality and enables
the engine control to react accordingly.
| Truck-Diesel is approx. 15 percent more efficient than motor car diesel |
The exhaust side of things was also pretty much settled. In utility vehicles the particularly economic, hot combustion with the respective SCR-follow-up preparation appeared to be asserting itself. The Euro-6 regulation burst the bubble. One could maintain the theory, that in the field of Diesel-injection, there is no calm development,
comparable with that of the petrol engine
exhaust gas, particularly as this is the beacon of hope for lower fuel consumption and lower CO2-emission. As a hybrid, it would be more welcome than the petrol burner, if in addition, the manufacturing
costs were to fall.
Let's limit ourselves to injection, in spite of the continued existence of the pump-jet in trucks, to the increasingly used Common Rail and even further, to it's injectors. Here a battle is going on between the Piezo-
system, which is offered by several suppliers and the magnetic valves still supported by Bosch (see picture). The latter have again become the subject of a great deal of attention, after Delphi, together with Mercedes
Benz, in the case of the so-called 'direct actuation', brought an unbelievable amount of defective injectors onto the market. This mishap, which cost millions, indirectly benefitted the tried and tested, reasonably priced
magnetic valves.
The problem with Piezo is obvious. Although one layer is very fast, it doesn't generate enough stroke. The necessary number of layers can apparently, not be accomodated. Thereby, direct actuation would be the ideal
target, especially in the case of small injection amounts, even moreso than the larger amounts. By the way, the test-cycle also depends on these to show evidence of the CO2-values. The dreaded
oscillations also take place in this region, which makes it difficult for the engine control to determine the exact volume regulation.
All in all, people seem to be trying various methods to reduce the oscillations. Either one directly actuates hydraulically or even machanically, or one places the Piezo technology very close to the nozzle-needle, thus
preventing the development of pressure oscillations, which lead to differing opening phases of the nozzle-needle. One could also measure the injection-pressures directly in the injector, thus controlling the next
injection accordingly.
Finally, we once again end up with Bosch, who generate more than 50% of their turnover in the automobile sector. They have again increased the peak-pressure, which is now at 2500 bar,
indeed, only in the mid- and heavy load area. Then, at least here, should up to 7 partial injections be possible, of course, more at full- than at lower partial load. Apparently, even higher pressures are in the
development stage. 10/12
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