Measurement&Analysis Of Transient Temperature Field Of Piston Of Marine Diesel Engine

The surrounding parts of combustion chamber contact with high temperature and high pressure gas directly when the diesel engine is in operating.The heat transfer characteristics between gas and the wall of combustion chamber will influence the working process in cylinder,thermal efficient,emission characteristics and thermal intensity.The temperature field is the main parameter for evaluating the heat transfer characteristics so it is the important basis for design of combustion chamber structure,cooling system and lubrication system.Numerical simulation and experimental study on the transient temperature fields of the combustion chamber's composition parts is significant important for improving the capacity of analyzing and evaluating the performance of combustion chamber's key components for it is effective for mastering the meathods of simulation and dynamic test,describing and analyzing the microscopic mechanism of heat transfer and distribution of heat transfer rate of diesel engine.The piston is a moving part around the combustion chamber.So the modeling and experimental test of the temperature field of piston are the most difficult and typically reseacch work.Considering piston as a research object,the paper has completed the research work in numerical transient temperature field modeling of the piston,influence factor analyzing of simulation precision,optimization of boundary conditions of 3D transient numerical simulation,development of high dynamic response temperature sensor and real-time wireless transmission system.1)A numerical model for simulating the 3D transient temperature field of piston has been developed.And the characteristics of piston's transient temperature field are analyzed in detail based on the piston of 620 single cylinder diesel engine.The results show that the temperature fluctuation of piston's transient temperature field mainly concentrate on the contact surface of piston and gas within 2mm from piston surface.The peak value of temperature transient change rate in this area can reach to 25?/ms.2)The influence on simulation precision ca ? sed by heat transfer coefficient of cooling chamber and heat transfer coefficient between gas and piston wall surface,piston ring set and cylinder liner is investigated deeply.By taking the temperature of feature points selected in gas side of piston,ring area and cooling chamber as evaluation index,the influence degree of different key parameters and boundary conditions on simulation has been studied.The numerical results provide clear insight of research emphasis and technical requirements for numerical simulation as well as experimental tests of piston's transient temperature field.3)The temperature field test system characterized by high dynamic response temperature sensor and real-time wireless transmission system is developed based on the characteristics of piston's transient temperature field and simulation's precision and verification requirements.The temperature element with high dynamic response has been developed through deeply analyzing the working mechanism of thin-film thermocouple.Then precise dynamic calibration of the system is finished by using a special high energy and short pulse laser calibration system.In this paper the in-cylinder real-time wireless data transmission system whose system bandwidth is not less than 100Hz has also been developed for data transmission.The test system developed can realize technical index with cam shaft resolution less than 1 CA and dynamic measurement error less than 1%,it can completely meet the experimental°verification requirements of transient temperature field,4)Experimental verification of piston temperature field is carried on 620 single cylinder diesel engine by using self-developed transient temperature field test system.The dynamic temperature data at key points of piston temperature field has been obtained.Simulation precision has been analyzed by comparing the results with experiments.The results show that the calculation error of dynamic temperature at some feature points is larger than 10%.This means that the numerical model which takes empirical formulas as boundary conditions can not guarantee good calculation accuracy.The main reason for this is because of the heat transfer coefficient between at gas side of piston is more complex been described by any available empirical formulas.The value of heat transfer coefficient in different area has several times discrepancies,it means that it is necessary to test and correct the boundary conditions by using the dynamic temperature test system.5)The optimization method of numerical simulation boundary conditions is investigated based on measured results and the simulation error is well corrected after optimization.A feasible process for optimizing boundary condition has been proved by ? sing the in-cylinder transient temperature test system and the reverse method.The optimization process is suitable for boundary conditions' optimization of any piston or other components of combustion chamber.