Search Results

This work was carried out as a part of a European project coordinated by Daimler Benz. The aim of this research programme was to reduce HC emissions of a petrol engine by using a newly designed carbon piston. The Mercedes-Benz mid-series four-valve petrol engine (M111, 2.2 litre) was used as the demonstration engine. A number of finite element (FE) analyses were carried out to predict thermal and mechanical stresses in the piston and optimise its shape. The original design of the piston was fully analysed under full load and maximum torque conditions. Results showed two critical areas in the piston with very high stresses and very low safety factors. A parametric study of various design features / dimensions was conducted to strengthen the design and improve its safety. Several specific features of the original design such as the crown thickness and pin hole profile, were modified to reduce stresses in the critical areas of the piston.

A general purpose computer model has been developed for analyzing the thermal performance of thermofluid systems. The system thermal behaviour is governed by heat convection and conduction. The model represents a thermofluid system as a thermal network, consisting of several different fluid circuits which are separated by solid walls. The solid walls are represented by hexahedral elements with lumped heat capacitance. The model has the capability to set up and link an equivalent thermal network from input data, using two types of junctions: wall-to-wall and fluid-to-wall. The flow calculations are based on the one-dimensional incompressible flow equation and the heat transfer calculations are based on either forced or natural heat convection for internal and external flows. The heat convection formulae used in the model are in the non-dimensional form which simplifies the program structure.