Thermal Load Analysis And Research For The Key Components In The Improvement Of High Power Specific Diesel Engine

This article is based on the project of improvement for high-speed terrestrial diesel engine, and the goal of this project is to improve terrestrial diesel engine to be a marine special high-power diesel engine. Thermal load is one of the conclusive elements that determine the project to be success or failure. Therefore, it is necessary to evaluate and analyze the thermal load for key components of diesel engine in order to assess the safety and reliability of improved diesel engine.The investigated subject of this article is cylinder head and cylinder of diesel engine, which works in specific condition, various exhaust backpressure condition and suction vacuum degree condition. Firstly, simulation for the thermal load of cylinder head and cylinder that works in specific condition is carried out by partitioned solution in Fluent and Ansys Workbench, and the heat transfer coefficient of firepower face and temperature field of cylinder and cylinder head can be obtained. Then input these heat transfer coefficients of firepower faces onto later calculations, and regard the temperature field of cylinder and cylinder head as one of criterions for thermal load. On the basis of previous results, simulations for the thermal load of cylinder head that works in different cooling water flux and cooling water temperature conditions are carried out by directly coupled solution, and the impact of cooling water on thermal load of cylinder head can be researched and analyzed. Finally, on the basis of previous method of calculations and the distribution of heat transfer coefficients on the firepower faces of cylinder head and cylinder, aiming at the improved diesel engine working in different exhaust backpressure conditions and suction vacuum degree conditions, the thermal load evaluation for cylinder head and cylinder is carried out so as to assess the safety and reliability, and then summarize the methods of thermal load evaluation.After a series of researches, the main results are obtained as follows:1. Both of partitioned solution and directly coupled solution have their own advantages and disadvantages, so the choice of coupled solutions should depend on project. Taking the computational controllability into consideration, partitioned solution is recommended at the beginning of thermal load calculation.2. Both the highest temperature of cylinder head and that of cylinder are lower than the critical temperature of thermal load of specific condition. Then their maximum thermal stress is also lower than the tensile strength. Therefore, the thermal load of key components is acceptable.3. Without regard for boiling of cooling water, both increasing the flux and decreasing the inlet temperature of cooling water can reduce the temperature of cylinder head, but raising the flux will increase the flow loss,and reducing the inlet temperature will raise the thermal stress. So, comprehensive consideration is needed in design and improvement of diesel engine.4. Both the increasing of exhaust pressure and suction vacuum degree of diesel engine lead to raise the temperature of fire power faces on the foundation of keeping the other parameters being constant.5. The improvement for diesel engine is reasonable according to the thermal load analysis and research for key components,which include cylinder and cylinder head.