Experimental investigation into simulated aging effects of common-rail injector nozzles: Influences on injection rate, spray characteristics, and engine performance

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 NO_x 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 NO_x 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.