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In this paper the experimental setup of a commercial third generation common rail solenoid injector with advanced measurement is discussed. The motion of the control piston is measured while performing injection rate investigations using a purpose-built injection rate analyzer of the Bosch type. At the same time fuel pressure in the feed line of the nozzle is gauged and contrasted to fuel pressure before the inlet connector. In contrast to the steady rise observed in a similar study, the motion of the control piston in this case is characterized by a changing gradient in the upward movement. The magnitude of the negative displacement of the upper part of the control piston due to the fuel pressure in the control volume corresponds to simulation results of the elastic deformation. Pressure before the inlet connector and pressure in the feed line exhibit a similar course with a difference in magnitude that is rising with higher rail pressures. Precisely with the end of injection the pressure in the feed line surpasses the pressure before the inlet connector for a short moment. The measurement results of control piston motion and pressure inside the injector are of particular interest because these parameters are to serve as indicators for changes in the injection rate caused by phenomena like wear and coking amongst others.Keywords common rail injector, injection rate measurement, eddy current sensor, control piston motion, feed line pressure IntroductionThe act of injecting diesel not only supplies the fuel for the subsequent combustion, but at the same time also determines the start of combustion with the diesel combustion process. This is unlike the gasoline combustion process, where injection and ignition are separated. Thus, the injection process is a major influence factor to consider in order complying with the increasingly severe emission legislation for compression ignition engines. Furthermore, alterations affecting the injection parameters of common rail diesel injectors that emerge during engine operation have been identified. Research efforts focused on brittle external nozzle deposits mostly consisting of carbon referred to as coking. In recent years, a type of sticky, the so-called internal diesel injector deposits (IDID) have appeared in production engines and caused needles to stick in common rail diesel injectors. It has been observed that the addition of certain additives (polyisobutylene succinimide; PIBSI) to diesel fuel, which are to inhibit the formation of coking deposits, have the side effect of contributing to the formation of IDID [1] [2]. These PIBSI react with acids that emerge from fatty acid methyl ester (FAME), a biodiesel supplement to common diesel in the European Union, to form IDID. Other major factors that influence the occurrence of IDID are high fuel temperatures and the content of aromatics and oxygen in the diesel fuel [2]. Deposits on the nozzle tip and inside the nozzle holes due to coking cause numerous adverse effects. It is proven that this type of deposits exe...

Emission performance of combustion engines has gained outstanding importance with both legislators and customers over the past years. Injector aging, such as nozzle wear or coking, results in the deterioration of injection and emission parameters. In this study, the influences of aging effects on injection rate, fuel spray as well as engine performance and emissions were assessed. Nozzles, which had previously been operated in a vehicle engine and were likely to have suffered from aging, showed no aging-induced characteristics during injection rate and spray measurements and were not investigated further. Therefore, nozzles with different nozzle hole diameters were utilized to simulate the different aging effects. Injection rate measurements demonstrated, that for smaller energizing times, a nozzle with smaller nozzle holes can deliver a higher injected mass than a nozzle with bigger nozzle holes. The adaptation of energizing time or injection pressure demonstrated the potential to compensate the change in engine load due to smaller or bigger nozzle holes. For bigger nozzle holes, the adaptation of injection pressure in order to restore the target load returned lower NOx emissions, whereas the adaptation of the energizing time always yielded lower soot emissions compared to the reference nozzle. For small nozzle holes, the optimization of the start of energizing reduced specific NOx emissions without increasing specific soot emissions. The comparison of measured injection rate and fuel spray characteristics to the ones reported in literature confirms the possibility of simulating nozzle wear by increased nozzle holes and coking by smaller nozzle holes. The results of this study are of vital interest to the research of aging effects and add useful knowledge about compensation methods for nozzle aging.

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