Influence of Boundary Conditions on Deformation and Stresses of a Cooled Piston in Diesel Engine
The effects of boundary conditions on the mechanical and thermal stresses of an oil-cooled piston in a diesel engine Scania DC09074A, as well as its deformation due to high combustion pressure and variable temperature, are discussed in this chapter. The deformation of the piston shape and von Misses stresses vary at the same boundary conditions due to different pin fixings in the piston centre. Since the piston transfers heat from the gas to the cylinder walls through piston rings, and some heat is transferred from the bottom surfaces of the piston to the gas within the crankcase, the piston is an indirect element in heat exchange in combustion engines. The piston loads were calculated using a 0D mathematical model with the Wiebe combustion model and the Woschni heat transfer model for a homogeneous mixture as assumptions. The CFD technique was used to precisely determine the gas temperature in the combustion chamber, and the simulation of compression, combustion, and expansion processes was carried out using the Fluent programme. The calculations were performed for two types of fuel: diesel oil and compressed natural gas (CNG). The compression ratio was reduced to ensure proper operation of the CNG engine. This was accomplished by reducing the combustion chamber’s volume. The overall stresses are not greatly affected by the piston change, according to calculations performed in the Ansys software. The total stresses and piston deformation at a fastened piston hub and a “floating” piston pin are compared in this chapter. The majority of calculations are based on the premise that the piston hubs are fixed, which is incorrect. In conclusion, the paper explains how to set boundary conditions for a “floating” piston pin. The deformation of the piston shape and von Misses stresses vary at the same boundary conditions due to different pin fixings in the piston centre. According to the findings, FEM piston calculations should be performed in conjunction with pin calculations to provide engineers with the necessary information on how to design the piston shape, which is typically “barrel-oval,” in order to ensure proper clearance between the piston and cylinder walls, particularly at high loads.
Author (s) Details
Cracow University of Technology, Al. Jana Pawla II 37, 31-864 Krakow, Poland.
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