Multifield Coupling Heat Transfer With3-D Working Process Simulation In An Internal Combustion Engine

The modern engine analysis is an important tool that helps design an engine with high efficient, low emissions and high reliability, in which the engine working process simulation and engine heat transfer analysis is one of the most important tools. Due to the complexity of the structure and the variability of the working process of the engine, for a long time, the related research work at home and abroad are respectively analyzing the working process and structure strength of the engine. However, due to the temperature field of the gas domain related to engine performance analysis, pressure, velocity, etc. with the engine structure analysis involves solid domain temperature field and thermal stress field is a mutual influence relationship, as a result, only establishing a complete and comprehensive multifield coupled model which coupling the engine working process with the engine heat transfer and thermal load can effectively take account of their mutual influence and help design a high-performance and high reliability engine.In this thesis, a3-D model for multifield coupling engine work process and combustion chamber heat transfer was built based on the FEM and CFD. The fluid domain was discretized by a block structured hexahedron grid, whose corresponding interface mesh is quadrilateral, and the solid (FEM) domain was discretized by an unstructured tetrahedral grid, whose corresponding interface mesh is triangle. Two special treatments for the grid generation were designed and utilized. In order to implement the coupled heat transfer model, a FEM program was developed, the KIVA3V code was improved, and a KIVA-FEM interface program was built. Then on this basis, the gas-solid coupled model was utilized to simulate the3-D work process and combustion chamber heat transfer of a gasoline engine. The result shows:(1)The temporal and spatial non-uniformity of thermal boundary conditions has an important influence on the steady temperature field of the chamber components, especially near the piston crown.(2)The temporal and spatial non-uniformity of thermal boundary conditions has an important influence on the transient temperature field of the chamber components, especially near the piston crown. However, the transient temperature wave of the combustion chamber components is limited in the area very close to the surface of the gas-side. With the distance increased from the combustion chamber wall, the transient temperature fluctuations weakened. When the depth reached1.Omm, the temperature fluctuation is not obvious, according to quasi-static temperature distribution。(3)The temporal and spatial non-uniformity of thermal boundary conditions has an important influence on the heat flux of the of the chamber components, especially during the blow-down period. During this period, a significant temperature fluctuation appears near the gas-side surface of the cylinder head, but there are no significant temperature fluctuations near the other surfaces of combustion chambers. Furthermore, the heat flux is very different among the different regions of the same surface of the combustion chamber.(4) The temporal and spatial non-uniformity of chamber wall temperature has a weak influence on the in-cylinder flow. The calculation results are no obvious difference when adopting uniform temperature boundary conditions and non-uniform temperature boundary conditions respectively. The temporal and spatial non-uniformity of chamber wall temperature influence the fuel evaporation in the early period of the fuel evaporative process. However, when close to the later period of the compression stroke, this influence is weak. The spatial non-uniformity of chamber wall temperature obviously influence the emissions of the NOx and SOOT, and it also influence on the distribution of NOx.