International Journal of Automotive Technology, Vol. 18, No. 4, pp. 729-742 (2017) DOI 10.1007/s12239-017-0072-y Copyright © 2017 KSAE/ 097-17 pISSN 1229-9138/ eISSN 1976-3832 729 OPTICAL DEVICE FOR MEASURING THE INJECTORS OPENING IN COMMON RAIL SYSTEMS Riccardo Amirante, Carlo Coratella, Elia Distaso, Gianluca Rossini and Paolo Tamburrano * Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Bari 70125, Italy (Received 18 November 2015; Revised 14 December 2016; Accepted 2 January 2017) ABSTRACT-Since the needle displacement exerts a fundamental influence on the operation of Common Rail injection systems, accurate measurements of the control piston position can be crucial for a more thorough analysis of the behaviour of injectors, in particular when multiple injections are employed. Eddy current sensors have traditionally been used in lab activities to measure the control piston position inside injectors; apart from the high cost, the scientific literature clearly shows their inadequacy, which is mainly due to the presence of electromagnetic disturbance: the current pulse, which controls the opening of the injector, generates electromagnetic fields which strongly affect the acquisition of data. Many attempts have recently been made either to solve the interference occurring during such measurements or to propose alternative displacement transducers whose operation is not influenced by electromagnetic interference. In this paper, a new device for measuring the injector opening is proposed: it is an optical transducer characterized both by simple and very cheap construction and by a reliable physical principle for measuring the control piston lift. The reliability of the proposed sensor is assessed by a thorough experimental campaign and by comparing the experimental results with the numerical predictions achieved by a Common Rail injector model. Since the assembly of the optical sensor does not affect the injector operation, it can efficiently be used both for experimental tests and for on-board diagnosis and monitoring of the injector operation. KEY WORDS : Common rail, Injector, Diesel engine, Optical sensor, Displacement measurement 1. INTRODUCTION The advent of the electronic Diesel engine control plays an important role in the development of diesel engines, in terms of performance improvement and optimization of consumptions. As is well known, the Common Rail (CR) MultiJet system has replaced the previous UniJet system, allowing Diesel engines to satisfy all the environmental targets (euro 3 and euro 4 standards) concerning the reduction in exhaust emissions and combustion noise (Tanaka et al., 2002; Celikten, 2003; Vanegas and Peters, 2009). However, in order to satisfy the stricter limits imposed by new European emission standards (Euro 5 and, after 2014, Euro 6), reliable predictions of the engine behaviour, including all the parameters affecting it, are required. Current research studies have been focused on the injection process. The effects of different parameters upon the quantity of fuel injected by a common rail injector was thoroughly analyzed by Bai et al. (2016). An effective one-dimensional spray model was developed by Xu et al. (2016), in order to understand the effect of gas flow on the penetration of diesel sprays. The impact of different injection types and after-treatment systems on particulate emissions of light-duty vehicles was deeply investigated by Oh and Cha (2015). Nanoparticles and other harmful exhaust emissions in accordance with injection strategies and air-fuel ratio changes for small diesel engines were analyzed by Eom et al. (2017). All the abovementioned papers along with other relevant research papers (e.g., the studies developed by Lim and Lee (2016) and Wang et al. (2015)) have provided advancements in modelling, predicting and understanding some important aspects regarding the injection process. In this scenario, this paper is focused on a very important aspect of the injection process, which is the measurement of the needle lift inside an injector. Infact, since the displacement of the needle exerts a strong influence on the injection performance, accurate measurements of the needle position can be instrumental in achieving a more thorough analysis of the behaviour of injectors. Precise knowledge of the needle lift during injections can also help researchers better investigate misfire in Diesel engines (which is due, as is well known, to injection problems) in order to improve current methods for detecting the phenomenon (Chang et al., 2002; Hu et al., 2011; Liu et al., 2013; Fan et al., 2014). Significant improvements must still be done as far as the measurement of the needle lift is concerned, in spite of the several advancements achieved in measuring systems for internal combustion engines, such as highly-effective measurement techniques for the characterization of particle emissions (see, e.g., the studies developed by Amirante et *Corresponding author. e-mail: paolo.tamburrano@poliba.it