Investigation Of Heat Transfer Characteristics For Non-road High Pressure Common Rail Diesel Engine

China has a complex terrain and a vast plateau.Atmospheric pressure,air density and oxygen concentration change with the altitude.These factors will affect the combustion process of the engine and make the heat flow distribution of the engine different.In addition,high temperatures are common in most area of China.High ambient temperature will reduce the air density,which leads to the decline of the heat transfer capacity of radiator and increase of engine heat load.The situation will affect the performance and reliability of engine.Therefore,the thermal management in high temperature and variable altitude environment has become a key problem to limit the performance of the engine.It is of great practical significance to study the heat transfer characteristics of diesel engine at high temperature and variable altitude for the formulation of engine heat load control strategy,the rational design and optimization of cooling system structure,and the study of engine adaptability to plateau environment.In order to understand the heat transfer characteristics,influencing factors and influencing laws of the cooling system of diesel engine in closed cabin in Plateau and high temperature environment,a two-cylinder turbocharged intercooled diesel engine was treated as the research object.The one-dimensional simulation model of diesel engine cooling system was established by GT-suite simulation software.The heat balance test of diesel engine under different altitude was carried out.The influence of different altitude(atmospheric pressure)on the heat flow distribution of diesel engine was analyzed,and the accuracy of the one-dimensional simulation model was verified by the test data.The effects of altitude and ambient temperature on the heat transfer characteristics of diesel engine cooling system were studied when the boundary conditions of the model were changed.AVL-fire simulation software was used to simulate the flow field of diesel engine cooling water jacket.The simulation results were analyzed and the jacket structure was optimized.The experimental results show that:1)At the altitude of 0?2 km,the average heat dissipation of coolant increases by 0.8 kw(about 1.83%)every 1 km;the fan mass flow,radiator convective heat transfer coefficient,radiator heat dissipation,radiator inlet and outlet temperature difference and engine inlet and outlet temperature difference decreased by 12.47%,13.30%,8.15%,8.88%and 4.19%respectively.2)When the altitude is 2 km and the ambient temperature is in the range of10?50?,the radiator heat dissipation,radiator convection heat transfer coefficient and fan mass flow decrease by 16.5%,3.57%and 3.64%respectively for every 10?increase in the ambient temperature;the cooling capacity of the engine cooling system is insufficient under the condition of high speed and high load when the ambient temperature is more than 40?,which cause the coolant temperature to exceed the limit value.3)Before optimization,the flow velocity of the cooling water jacket is low(the average flow velocity is less than 0.5 m/s),and the flow field distribution in some areas is unreasonable,which is difficult to meet the cooling requirements.The cooling strength of the cylinder head and block is significantly improved by increasing the inlet flow of the cooling water jacket.By optimizing the structure of the water inlet of the cylinder head water jacket and the connecting water hole of the cylinder head water jacket,the pressure concentration near the inlet of the water jacket of the cylinder head is eliminated,and the cavitation corrosion is avoided.In addition,the mobility of the upper part of the cylinder-block-water-jacket is significantly enhanced,the flow field distribution is more reasonable,and the flow uniformity of the whole water jacket of the cylinder block is significantly improved.