Optical Sensor for the Needle Lift Detection in the Common Rail Injector

The detection of needle displacement within a Common Rail injector is a crucial step to suitably characterize the behaviour of an injector. The needle motion is traditionally measured by means of an eddy current sensor. Apart from its high cost, scientific literature highlights its drawbacks, such as the introduction of mechanical weakness on the control piston as well as the electromagnetic disturbance affecting data acquisition. In order to provide an improved quality of signal, other solutions have been developed, which require a large number of components, leading to increased layout complexity. This layout can create a packing issue while mounting the sensor on the test rig. A novel sensor (UK Patent Application No.1819731.9) using fibre optic cable has been designed and built to overcome the limitations typically associated with needle displacement transducers. Variations in light intensity, stemming from control piston displacement, underlie the working principle of the proposed sensor. The paper provides technical details and describes the experimental tests proving the sensor capability to detect injection events under various injection scenarios. The use of the new sensor highlighted the key relationship between injector needle lift and backpressure. Given the cost-effectiveness and the downsized layout, the sensor serves as a crucial step towards the thorough understanding of injection process.