Influence of aging of a diesel injector on multiple injection strategies

Abstract

Multiple injection strategies have contributed to the improvement of thermal processes in Internal Combustion Engines. On this matter, the correct performance of the injector is a critical factor in the implementation of these techniques, as changes in the behavior of the injector could affect the injection development, altering the combustion process and heat transformation efficiency. Thus, the present study analyzes the development of multiple injection events in a diesel injector aged due to partial obstruction of the holes of the nozzle. To this end, a multi-hole piezoelectric injector was employed, in which the aging of the injector is evaluated through momentum flux measurements for each hole. Afterwards, rate of injection tests with pilot and post injection strategies are performed, and the results are compared to the injection events made by the same injector before aging. The results provided by the momentum flux experiments confirmed the partial obstruction of two holes. Furthermore, rate of injection comparisons showed that the injector had a lower steady-state rate of injection after aging and required a longer time to end the injection. These phenomena affected the multiple injection events, as the extended time required to end the injection reduced the hydraulic dwell time between pilot/post injection and the main injection. Furthermore, for short dwell times, this phenomenon led to the unification of the main and post injection, resulting in a large single injection. Hence, not only an increase in fuel consumption would appear, but the thermal benefits of implementing the post injection would be lost.