## 2 Materials and Methods
### Research Method  
The choice of sensor location significantly impacts the quality of the information in a given signal and the accuracy of diagnostic decisions [3,9,10]. Based on preliminary studies [3,9,10,30,31], the following measurement points were selected: engine component locations with the highest unreliability and the area with the highest vibration signal generation level. The vibration signal, recorded anywhere on the engine body, is a weighted sum of the responses to all elementary events. The weights are convolutions with impulse functions of the transition from the place of generation to the reception of the diagnostic signal. The received vibration acceleration signals were in three channels, and each channel took a component of the vibration signal in one of three directions: parallel, horizontally perpendicular, and vertically perpendicular to the axis of the injection pipe. One of the methods of obtaining diagnostic information is the measurement of vibrations generated by a piston combustion engine. Therefore, an attempt was made to diagnose marine diesel engines using vibration signals in various directions and simultaneously measuring the pressure signals in the combustion chamber and vibrations [31]. The architecture of a computer measurement system that provides support for sensors in terms of the power supply, signal loading, the preprocessing of the measured analog signals, synchronous or asynchronous analog-to-digital processing, analysis of selected signals and their archiving, and the transfer of signals to the database and knowledge base was presented in previous studies [9,32]. The measurement system consisted of vibration accelerometers and preamplifiers from Bruel and Kjaer, a photo-optical crankshaft position sensor, a terminal block, and a portable computer (Figure 2). The accelerometers were attached to the injection pipe with a portable bracket. As a result, the design of the injection subsystem was not affected, which is a requirement for classification societies. During diagnostic tests, passive and passive-active diagnostic experiments were conducted. The tests were carried out for all cylinders with the same repetitive loads, resulting from the power consumption of the receivers under the natural conditions of a seagoing vessel. Rotational speeds were nearly nominal at the same level as the internal combustion engine that drove the generators. The measurements of vibration accelerations were performed at experimentally determined points of the injection subsystem for various types of diesel engines in addition to the type 6 AL20/24D presented in this article in a sea vessel. Figure 1: View of the nozzle of the injector \(159\times 9\times 023R\) with a piece broken off (**a**) and the turbine rotor damaged by fragments of the nozzle (**b**). The following parameters were determined during the acquisition and analysis of diagnostic signals: analysis domain, frequency bands, the number of signal averaging, the use of filters, etc. The effect of the frequency band on the analysis results was examined, and the selected band for these tests ranged from 0 to 10 kHz for vibration acceleration signals and from 0 to 2.5 kHz for the in-cylinder pressure signals. The DaqView computer program from IOtech was used for signal acquisition. DaqView is a configuration and measurement software that operates with measurement systems from various companies. The integrated data acquisition system consisted of a device archiving a large volume of data in the main memory, controlled with a portable computer, and recording and analyzing systems. This enabled the configuration of the devices and measurements. This software allows one to select these settings, observe the measurement results, and save them in real time. Using this program, selected signal analyses were performed in various domains, and the resulting data were transferred to other programs.