Quantitative Indicators of the Instantaneous Speed of a Ship’s Main Engine and its Usability in Assessing the Quality of the Combustion Process

Abstract

A graph of the changes in an engine’s operating speed can be used to assess the quality of the combustion in its cylinders. In this paper, the authors carried out tests on a Buckau-Wolf R8VD-136 ship engine, which was directly driving the propeller. This engine is owned by the Laboratory of Marine Engine Rooms at the Maritime University of Szczecin. For standard rotational speeds ranging from 200 to 280 rpm, with increments of 20 rpm, the authors measured the changes in the instantaneous speed for the engine’s normal operating conditions (reference graphs) as well as with one of the cylinders being out of operation. A no-combustion situation was successively introduced into each cylinder for each preset rotational speed. The obtained graphs of the instantaneous speed were then used to determine certain quantitative indicators, which the authors believe can provide information about the technical condition of the engine. The analysis concerned the averaged graphs of the speed under the conditions set for five consecutive engine operating cycles. The indicators that were calculated included the maximum difference in the speed over the engine’s full operating cycle, the uniformity of the engine speed and the differential speed area factor, the latter a term that has been proposed by the authors. The values of the individual indicators that were obtained from the reference graphs and the graphs with no combustion in one of the cylinders were compared. All indicators are sensitive to cylinder misfire. Conclusions were then drawn on the usefulness of these indicators in assessing the condition of an engine.

Spectral Analysis of Torsional Vibrations Measured by Optical Sensors, as a Method for Diagnosing Injector Nozzle Coking in Marine Diesel Engines

“…There are some commonly known ways to diagnose engine operation based on the fluctuations of angular velocity of the flywheel. Under specific engine operating conditions, changes in instantaneous angular velocity may be a source of information on the incorrect operation of specific cylinders [ 19 , 20 , 21 , 22 ]. Considering the fact that instantaneous velocity is a derivative of displacement in time (displacement is the function of time, thus it is a classic example of a derivative function based on its argument), a decision was made to check whether this signal may be relied upon for diagnostic purposes.…”