A new optical sensor for the measurement of the displacement of the needle in a Common Rail Injector

Since the needle displacement exerts a fundamental influence in the operation of a Common Rail Diesel injection equipment, an accurate measurement of the instantaneous position of the control piston is crucial for a more thorough analysis of the behavior of the injectors, in particular when multiple injections are employed. Moreover, the development of a cheap instrumentation would allow to enlarge the Diesel engine on-board equipment with an instrumentation for the diagnosis of the injector operation. Eddy current sensors have been traditionally used in lab activities to measure the position of the needle inside the injector; apart from its high cost, the scientific literature clearly shows their inadequacy, given the presence of electromagnetic disturbance: the current pulse which controls the opening of the injector nozzles generates electromagnetic fields which strongly affect the acquisition of data. Many attempts have been made either to solve the interference occurring during the measures or to propose a displacement transducer whose operation is not influenced by electromagnetic interference. The sensor that will be proposed in this paper (Patent filing October 2012, under submission for PCT extension) follows the latter line: it is an optical transducer which joins the simple and very cheap construction with the employment of a reliable physical principle for measuring the needle lift. The paper provide all technical and scientific details of the operation of the proposed sensor, as well as a wide proposition of experimental applications aiming at assessing its capability of detecting also multiple injections