Abstract
This article characterises the methodology for the endoscopic testing of a laboratory diesel engine used for testing marine fuels. The ‘Shadow’ measurement method used in the XLG3 type EVEREST digital endoscope, for quantitative and qualitative identification of detected surface defects, was approximated. Representative endoscopic images of the elements limiting the working space of the research engine are demonstrated, having been recorded during the usable quality testing of newly produced, low-sulphur marine fuels, so-called ‘modified fuels’. The main purpose of the endoscopic examinations was the final verification of the tested fuel’s suitability for feeding full-size marine engines.