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 pollutant emissions and fuel consumption, researches are focusing on improving the efficiency of combustion engines. Among the strategies being applied to this end, having precise control of the timing and amount of fuel mass injected is proving to be critical in the combustion efficiency of multiple injection techniques. However, the aging of the injector and its effect on the mass injected is still unclear. In this work, the behavior of 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 rate of injection measured at the beginning of its lifetime to the rate of injection provided by the injector after extensive use, maintaining the same injection conditions in both measurements. Injection pressures up to 200 MPa were used throughout the experiments. The results showed that, for the same energizing time and voltage signal, the steady rate of injection was lower and longer in the measurements taken after extensive use. Specifically, 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 some holes were partially obstructed. Thus, the presence of coking in the injector was attributed as the cause of the difference seen in the rate of injection. In this sense, the difference in pressure between the control volume and the nozzle is bigger, leading to a longer time required by the needle to descend and end the injection.
Raul Payri, Francisco Javier Salvador, Jaime Gimeno, Tomas Montiel