High Fuel Utilization in Solid Oxide Fuel Cells: Experimental Characterization and Data Analysis with Continuous Wavelet Transform Angelo Esposito a, * , Luigi Russo b , Christoph K € andler a , Cesare Pianese b , Bastian Ludwig a , Nadia Yousfi Steiner c a European Institute for Energy Research (EIFER), Emmy Noether Strasse 11, 76131 Karlsruhe, Germany b Department of Mechanical Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, SA, Italy c Laboratory of Excellence ACTION, FEMTO-ST (UMR CNRS 6174)/FCLAB (FR CNRS 3539), University of Franche-Comt e, Rue Thierry Mieg, F90010 Belfort, France highlights  High Fuel Utilization in SOFCs was studied experimentally and numerically.  An experimental procedure was developed to characterize SOFC under high fuel utilization.  A micro-CHP system was characterized with the mentioned test procedure.  Continuous Wavelet Transform was applied to the voltage to develop a diagnostic tool.  Signatures were found for different fuel utilization levels. article info Article history: Received 2 April 2015 Received in revised form 21 February 2016 Accepted 18 March 2016 Keywords: Fuel utilization Solid Oxide Fuel Cell On-line diagnostics Fault detection Continuous Wavelet Transform abstract The on-line diagnostics of Solid Oxide Fuel Cells (SOFCs) is a critical tool to achieve optimal performance and extend the lifetime. The Continuous Wavelet Transform (CWT) methodology was applied to the SOFC voltage signal to detect signatures that reveal the presence of a fault in the cell/stack. The selected fault was anode re-oxidation caused by high Fuel Utilization (FU) (higher then nominal). To experimentally emulate the high FU faults, a standard test procedure was developed, which was used to characterize a m- CHP system at high FU operation. To complete the analysis, data collected on Single Cells were exploited too. The CWT was applied to the voltage signal for each FU level to verify the qualitative difference (signature) between the signals at different FU's within the same tests as well as the correspondence between the same conditions over different tests. A statistical study was performed to quantify the observed differences and to determine the correspondence between CWT coefficients and operating conditions. The approach proves to be suitable to diagnose high FU in SOFC, showing a successful detection rate above 76%. The results show the good potential of using the CWT methodology as diag- nostic tools for SOFCs from cell to stack level. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The Solid Oxide Fuel Cell (SOFC) technology is nowadays widely recognized as a promising alternative solution for Auxiliary Power Units (APUs) and Combined Heat and Power (CHP) systems, to meet the targets of higher efficiency and lower carbon dioxide emissions [1]. Although many achievements, such as high efficiency, fuel flexibility, and low emissions show the benefits of this technology, crucial bottlenecks, such as low durability and reliability, still need to be overcome. Reliability targets have been set in the USA, European Union (EU) and Japan. For instance, the EU commission has set the target of 5000 h lifetime for transportation applications, which is the mini- mum requirement for vehicles in practical use; while the target for stationary applications has been set to 40.000 h of operation. * Corresponding author. E-mail address: angelo.esposito@gmail.com (A. Esposito). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2016.03.069 0378-7753/© 2016 Elsevier B.V. All rights reserved. Journal of Power Sources 317 (2016) 159e168