Aging of a Multi-Hole Diesel Injector and Its Effect on the Rate of Injection 2020-01-0829

In order to comply with the increasingly restrictive limits of emissions and fuel consumption, researches are focusing on improving the efficiency of combustion engines. In this area, the aging of the injector and its effect on the injection development is not entirely analyzed. In this work, the rate of injection of a diesel injector at different stages of its lifetime is analyzed. To this end, a multi-hole piezoelectric injector was employed, comparing the injection rate measured at the beginning of its lifetime to the rate provided by the injector after aging, maintaining the same boundary conditions in both measurements. Injection pressures up to 200 MPa were used throughout the experiments. The results showed that the steady-state rate of injection was lower after the injector aged. Furthermore, the injector took a longer time to close the needle and end the injection, in comparison with the measurements done at earlier stages of its lifetime. To explain this phenomenon, measurements of momentum flux for each injector hole were done, and results showed that two holes were partially obstructed. Thus, the presence of coking in the nozzle of the injector was considered as the cause of the differences between stages seen in the rate of injection. In this sense, a reduction of the effective outlet holes area due to deposits would restrict the flow rate. Moreover, the pressure in the nozzle due to the contained fuel is extended, leading to a longer time required by the needle to descend and end the injection. Then, aging of the injector was attributed to deposits in the nozzle holes. This phenomenon could result in an inhomogeneous spray distribution, which should be taken into account when designing the combustion process.