Nguyen V. Piston of a medium-speed diesel engine construction designing using the modified method of thermal-stress state analysis

The paper deals with the existing and proposed methods of modeling the temperature and thermal stress of the composite piston on a constant and transient modes of diesel operation, the use of which allowed to offer a new design of the piston diesel type D-100 whose weight is reduced by 45% (up to 22 kg). An algorithm for the process of determining boundary conditions (BC) for pistons is proposed. It is shown that the transition time should be taken into account when determining the BC for non-stationary modes of operation. For this purpose, the temperature of the piston, the thermal properties of the working fluid and the means of cooling over time are determined. The BC models are designed for all piston surfaces - combustion chambers (CC) - through a workflow model; internal - oil-cooled; lateral - subject to clearance and / or contact. BC on short circuit is defined by the developed program of thermal calculation of the work process, which allowed to study the model process using known formulas of heat exchange (α-formulas). It has been shown that the GB-Rosenblitt α-formula is best suited for D-100 diesel studies. BC on the inner surface of the piston is determined by the variable acceleration of the piston. BC on the side surface is determined by the variable speed of gas movement in the gap. Formulas for determining the coefficient of heat transfer of gases in the gaps with the piston wall are proposed. Simulation at all stages of work was carried out for both the proposed and for comparison for the standard piston. It is shown that the new design is colder up to 40K (on the surface of the piston CС) and voltage less than 30 MPa (on the surface of the piston CС).