Empirical assessment of thermodynamic processes of a turbojet engine in the process values field using vibration parameters Marek Waligórski ⇑ , Karolina Batura, Karolina Kucal, Jerzy Merkisz Poznan University of Technology, Faculty of Civil and Transport Engineering, Piotrowo 3, 60-965 Poznan ´, Poland article info Article history: Received 23 October 2019 Received in revised form 21 January 2020 Accepted 29 February 2020 Available online 10 March 2020 Keywords: Turbojet engine Diagnostics Combustion process and its irregularity Vibroacoustic methods Empirical research Faults detection abstract The possibilities of the vibration accelerations signals parameters application for the assessment of ther- modynamic processes in the turbojet engine of the F-16 airplane given in its real work conditions have been presented in the paper. The aim is early detection of negative changes in the mixture formation and combustion processes taking place at the aircraft turbojet engine to maintain the high overall efficiency and safety of aviation tasks. Diagnostics of combustion and injection processes have been conducted for stationary engine investigations in the way to obtain quantity measures (dimensional and non- dimensional) and characteristics for these phenomena in the process value domain. The quality of the fuel injection and combustion, expressed in engine operation parameters of the best sensitivity, has been linked to the particular vibration impulse and energy representations, giving the important functional relations for building a diagnostic system for turbojet F-16 airplane engines for real operating conditions. The results show the proposed method assures early and accurate diagnostics for engine dynamic char- acteristics, making possible diagnostic system application. The diagnostic system design for combustion and injection processes monitoring and malfunctions detections has been proposed. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction The problem of evaluation of short-time dynamic processes (in the sense of high variability of changes occurring within a given process run, not the conditions in which the research is carried out) occurring in turbojet engines of aircrafts used in military avi- ation is extremely important for this kind of transport. The above issue is of paramount importance for the assessment of aircrafts throughout their operation time, based on monitoring the correct- ness runs of main and accompanying processes, and diagnostics of the technical object, so as to verify the changes in parameters and operational characteristics of the engines, resulting from the wear processes and to detect the first symptoms of disability (of struc- tural and process sources). The main goal in the above process is not only to maintain the highest level of the engine overall effi- ciency, but also to assess the proper operation of individual engine components and structural capability of its components to ensure the implementation of aviation tasks with the high value of safety indicators. The fuel injection and mixture combustion processes carried out in the continuous air flow through the turbojet engine influence on the above efficiency significantly (directly in the form of mechanical, thermal and vibroacoustic loads) on the structure and service durability of kinematic pairs and the engine subassem- blies components. The current accurate assessment of the combustion and fuel injection as well as other dynamic processes requires application of appropriate measurement tools that will provide clear and quick responses to the qualitative and quantitative changes in the tech- nical facility, resulting in changes of the operational functions effi- ciency and their specific impact on the efficiency of mechanisms and security. Therefore, one should look for a method that can be used in the real operation conditions, without changing the accu- racy of the diagnostic assessment, when the application of an appropriate method for diagnosing a turbojet engine is being con- sidered. Different methods for engines diagnostics [1–10,13– 17,20] have been discussed in the worlds literature (related to achievements in the considered topic), but most of them are con- nected with internal combustion engines and their stationary and traction applications. The research of turbojet engines in their real operation conditions, especially of the military applications, have been discussed only in few of them. It has been assumed that vibration methods can be used for this kind of tasks, and unam- biguous functional relations between the main and accompanying processes can be obtained using the detailed analysis of the vibra- tion acceleration signal and the determination of point measures https://doi.org/10.1016/j.measurement.2020.107702 0263-2241/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: marek.waligorski@put.poznan.pl (M. Waligórski). Measurement 158 (2020) 107702 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement