Simulation Analysis And Optimization On The Scavenging Process For The Uniflow-scavenged Diesel Engine

Valve-inlet type, large-bore low-speed uniflow-scavenged two-stroke cycle diesel engines are increasingly being used in ships as they have the advantages of high efficiency, high power, reliability, long life and so on. However, a two-stroke engine doesn't have separate scavenging stroke, which makes its scavenging quality poorer than that of four-stroke engines. Therefore, its performance depends largely on the degree of perfection of the process of scavenging. When the process of scavenging is to be perfect, there is less exhaust gas and more fresh air in the cylinder, which creates conditions for the good combustion of the fuel. This improves dynamics of the engine, reduces pollution emissions, and improves overall reliability of the engine.The paper takes the method of numerical simulation to study the scavenging process of a two-stroke engine. It verifies the model established first, and then makes an optimization of the intake port by varying the angle of elevation of the scavenging port and the size of radial angle of slope. The paper conducts numerical simulation of various models, and predicts which model's scavenging quality is more perfect so as to guide the inlet structural design.This paper takes 6S50MC-C engine as its base of study object. It uses PRO-E 3D drawing software to model according to their relevant design sizes first, and then uses AVL-BOOST software to conduct preliminary calculations to get the boundary conditions. At last, the paper uses AVL-FIRE software to conduct three-dimensional simulation calculation of scavenging process of the established model. We can see from the results of the simulation, when the angle of elevation of the scavenging port is big, it is conducive to pre-ventilation, however, there will be a more serious mix of exhaust gas and fresh air, and the scavenging quality depends on the engine speed. When the speed is big, it is good to have a certain angle of elevation, on the contrary, it need not have the angle of elevation; it is suitable for the radial angle of inclination of the scavenging port to be 20°or so. In summary, this paper has a certain guide to the design of air-port structure of the uniflow-scavenged two-stroke cycle diesel engines.