USE OF NUMERICAL PROFILES OF THE WORKING PROCESS TO DETERMINE DYNAMIC PHASES OF EXHAUST VALVE CLOSURE OF A TWO-STROKE LOW-SPEED DIESEL ENGINE

The existing practice of diagnosing main and auxiliary engines by parameters of the working process in the merchant fleet, in the world of modern trends in the field of their operation, requires a significant revision of approaches. The increase in prices for oil fuels and the tightening of environmental standards have led to a significant decrease in commercial speeds of ships, which, in turn, has led to an increase in the operating time of main engines in partial load modes. In practice, ship mechanics are faced with the fact that during the entire voyage there is no possibility to simulate the engine in conditions that allow obtaining indicator diagrams suitable for comparative analysis with reference profiles obtained by the engine manufacturer during its bench tests. This problem can be solved by constructing numerical profiles of the working process based on the results of bench tests of the engine. The presence of such a profile allows you to obtain a reference indicator diagram for any operating mode, however, for an objective comparative analysis of the obtained during operation and reference indicator diagrams, even the presence of the latter may be insufficient. The peculiarities of the organization of gas exchange processes in two-stroke low-speed engines impose certain restrictions on the use of traditional methods of processing indicator diagrams, requiring the consideration of additional parameters, including dynamic valve timing. The design features of the gas distribution elements of these engines lead to the fact that their technical condition can significantly affect the moment of the start of the compression process, and therefore the parameters of the entire working process. The main gas distribution element of this type of engine is the exhaust valve, which has a hydraulic drive, which is driven either by the camshaft or through a pressure multiplier with electromagnetic control from the electronic engine control system. Regardless of the control method, the design of the hydraulic transmission has certain features that lead to differences in static valve timing from real, dynamic ones. This study by the authors is devoted to the study of dynamic phases of exhaust valve closing using numerical profiles of the working process.