Features of hydrody-namics and heat exchange in the cavities and the temperature state of the pistons oil-cooled diesel engines

The article notes the need to reduce the thermal load of pistons while increasing the power of diesel engines to ensure the reliability and service life of the cylinder piston group. Taking into account the insufficiency of reducing the thermal load only by improving the combustion process and the working cycle as a whole, methods of forced cooling of diesel pistons are substantiated and analyzed. The specifics of the movement of lubricating oil in the cooling cavities and the features of its hydrodynamics are noted, due to both the method of oil supply to the cavity and the nature of oil movement in the cavity with varying degrees of filling of the cross section, causing laminar, turbulent and transient modes of movement. A feature of hydrodynamic phenomena is the dependence of the area of the inner surface of the cavity washed with cooling oil as a function of the degree of filling of the cavity and the flow of lubricating oil through the cavity. The design features and functioning, both in static and dynamic modes, of non-motorized stands for studying the geometry of the nozzle of the oil supply nozzle, which ensures the consumption of oil supplied to cool the piston and the degree of expansion of the jet to minimize return losses when oil enters the inlet oil intake channel during piston movement are described. The geometry of the inlet oil intake and outlet drain channels, the oil levels in the cavity and the degree of its filling as a function of flow are determined. It is noted that increasing the crankshaft speed reduces oil consumption through the cooling cavity and increases return losses. Using literature sources and computational and experimental procedures, the nature of oil movement in the cooling cavity is analyzed and the dependence of the heat transfer coefficient from the piston to the cooling oil, the amount of heat given by the piston to the cooling oil, the oil temperature at the outlet of the cooling cavity and the temperature of the characteristic points in the piston section on the oil flow through the cooling cavity in the piston head of a transport diesel engine is presented. A pattern is presented that relates the relative consumption of cooling oil through the cooling cavity and the area of the inner surface of the cavity, obtained by the authors, and makes it possible to evaluate the effectiveness of various shapes of the cross-section of the cavities using the proposed cross-sectional shape indicator. Using the boundary conditions of heat exchange in the cavity, determined using the stated provisions on the features of hydrodynamics and heat exchange in the cooling cavity, the influence of local oil cooling on the temperature state of some piston designs is analyzed.