Optimization of engine thermal management systemEngine thermal management is from the angle of the whole system, integrated control engine, turbocharger and exhaust, cooling system and engine cabin heat transfer etc., improve circulation efficiency, reducing heat load, change control engine components of high and low temperature limit, temperature distribution and regularity, improves the cooling capacity of the engine's colleagues, keep the engine in good power nature, economy and emission performance and reliability.Application of engine thermal management system technology, can effectively heat transfer system involved in the engine as a comprehensive system of consideration and get the accurate boundary parameters of the engine each fluid system, precise control of temperature and heat flux of each system, can guarantee the safe and efficient operation of the key components and system control. And the optimization of the heat transfer process, reduce the size and power consumption of cooling system, reasonable utilization of heat energy, reduce waste emissions, improve energy efficiency, reduce environmental pollution. There is significant difference between engine thermal management and traditional engine cooling system. From engine cooling to engine thermal management is not only a technological progress, but also a breakthrough in management and design ideas. Engine thermal management technology has become an important measure of engine energy saving, emission reduction, power performance, reliability and engine life.The cooling fan mechanical drive cooling system in the traditional fan from the engine crankshaft through a belt drive, the cooling air depends on engine speed and engine speed is proportional to, rather than the actual engine operation cooling capacity, unable to accurately control the air flow through the radiator, thereby it is difficult to make the engine work in the best temperature, resulting in emissions is too high, the fuel economy and engine performance deterioration. In addition to the outside of the traditional cooling fan cooling sensitivity adjustment is not high, the power loss is also large, serious power consumption, such as power consumption of the fan can reach the total output power of the engine 10%. In order tosolve the problems appeared in the self controlled electric fan, the electric fan speed according to the coolant temperature and air conditioning cycle parameters to adjust, through the sensor and computer chip according to the engine temperature control operation, to provide the best cooling medium flow and fan speed to adjust cooling capacity, reduce heat loss, the engine at low temperature when the power loss, and excessive wear, inhibit the engine overheating, reducing noise and fuel consumption. The cooling fan of transforming the traditional control mode for intelligent control, the cooling capacity of cooling fan with engine cooling and automatic precise adjustment, improved engine preheating velocity, water temperature too hot or too cold to prevent, to maintain the best working temperature, but also avoid wasting a lot of energy, which reduce the fan 90% power consumption, save fuel 10%. In addition, in order to improve the efficiency of cooling fan, replace the arc straight blade cooling fan with a plastic fan wing; with wing section plastic and streamlined hood, the formation of streamline flow in the fan airflow entrance, can improve the efficiency of hydraulic fan. Finally, the efficiency of electric fan is 85%.The traditional mechanical driven cooling water pump is driven by V or gear, and the running speed is proportional to the engine speed. Many studies show that the traditional water pump in water only 5% of the time is right, not the precise control of the flow through the radiator cooling medium, so it is hard to make the engine work at the optimum temperature, fuel economy and engine performance. The electronic control pump driven by the motor, the flow can be independently controlled. The electric pump without crankshaft drive, the installation location is flexible, can optimize the water pump characteristic design, at the same time because there is no gear or belt wheel drives, reduces cycle lateral V belt and gear of the pump bearing load capacity, reduce the loss of driving. According to the requirements of engine cooling, not only the speed of cooling water is supplied by the electronic control pump, but also the cooling state of the part load and the high speed condition is avoided, and the unnecessary power consumption is reduced. Guo Xinmin on the domestic loader cooling system control device is studied, in order to achieve automatic adjustment of cooling water pump speed regulating overflow flow proportional relief valve according to the temperature of cooling water by using scm. The results show that, when thetemperature is low, the control can reduce the preheating time by 50%, increase the heating speed, and save the fuel in the preheating stage by 43%. In 1999 Valeo proposed a new electronic tuning system in the engine to improve engine cooling performance. It realizes the separation of the pump and cylinder, flow and ventilation device of the pump to adjust and control the engine ECU, convenient pump installation, and away from the cylinder heat source, the pump can be made of plastic, which can reduce the cost and reduce the weight of the pump, the pump speed changes with temperature to achieve the change, further reducing the heat loss and mechanical loss, reduce pollution and fuel consumption. Stepanoff has put forward the design theory of high efficiency centrifugal pump and axial flow pump, which can improve the efficiency of engine cooling water pump to 75% by changing the shape of impeller and improving the surface finish. Japan NISSAN, this theory developed a water pump based on the structure by reducing the size of pump, the company also improved by increasing the number of blades, blade curve design, the maximum pump efficiency reached 75%.The thermostat thermostat function is automatically adjusted according to the cooling water into the radiator temperature of the water, change the water cycle range, to adjust cooling capacity of the cooling system, ensure that the engine work in the suitable temperature range. The thermostat is a key component to control the cooling flow path of the engine cooling system, but at present most of the thermostat using paraffin as temperature sensing medium, the existence of "delay" and "hysteresis", unable to meet the precise control of the cooling system, the engine fuel consumption, service life shorten. In order to further improve the cooling efficiency of the engine, electronic thermostat came into being. The control system of the temperature controller is composed of a sensor, a motor and a control module, which can control the coolant flow rate according to the coolant temperature or the temperature of the engine parts. When the engine is running, the control unit according to the calculated values obtained by the sensor signal conditioning unit load voltage to the temperature, the dissolution rate by controlling the load voltage to control the size of paraffin, then effectively quickly and accurately control the size of the circular opening, so that all parts of the engine is always in the optimal temperature range, in order to improve thecombustion efficiency of fuel oil increase the air intake quantity, reduce wear and prolong the service life of the engine. In 1997, the United States University of Oakland X-ZHOU and B.CAHLON et al introduced hysteretic delay differential equations to describe the dynamic characteristics of the thermostat in the engine cooling system in the work process, and gives the numerical solution of the model algorithm. 2002 ~ 2006, the United States Clemson University John R.Wagner et al. Carried out the engine cooling system intelligent thermostat. They use the servo motor to drive the gear and screw, and then screw the rotation of the movement into the piston (spool) of the telescopic movement, so as to achieve the size of the cooling fluid circulation channel switch. In 2009, T.Mitchell et al. Compared the effects of 4 different types of thermostat arrangement on the performance of the engine cooling system under the condition of warm air. They are in the use of paraffin thermostat, electric two way valve, electric three-way valve and do not install thermostat, respectively, in the 4 cases of engine warm-up test. Their study suggests that the use of electric three-way valve in this form, the engine warm-up time and fuel economy performance of the best. In 2004, Tsinghua University, Luo Jianxi, Zhang Yangjun et al. Analyzes the influence of thermostat on dynamic performance of the engine they pointed out: the effect of interaction of delayed nonlinear dynamic characteristics and the system of the thermostat, causing the engine dynamic characteristics of complex thermal system. When the temperature of the thermostat is short, the temperature deviation is small, and the temperature of the thermostat is weak, the inlet temperature of the engine is small, the time needed for stability is short, and the adjustment effect is good.The cooling water cooling fluid flow, pressure and reasonable flow field distribution have a direct impact on the cooling effect of the engine. The engine passes the water jacket to the cooling system, and the reasonable design of the water jacket is the key factor to the cooling effect of the engine. The water jacket structure reasonable first to ensure the uniformity of water jacket wall thickness, wall due to heat in some areas caused by the unreasonable distribution of the water jacket wall thickness of the engine stress occurred the situation; secondly, to ensure the rationality of the water jacket cavity, the cooling liquid can be normal flow in the water jacket, no flow dead, caused by overheating in some parts of theengine; in addition to ensure water supply to all parts of the engine should be reasonable, each cylinder of the engine combustion chamber wall temperature as possible. Improved engine cooling water jacket structure for flow field distribution right, can improve engine thermal load and thermal stress, prevent engine damage, improve the engine service life of the parts, engine power and fuel economy. Couetouse H. et al. Proposed the design of a split flow system in 1984, that is, the steam cylinder head and the cylinder body have different cooling loops, which are suitable for the cylinder head and cylinder body with different temperatures. This is due to the lower cylinder head temperature is conducive to air intake and improve emissions, while the higher cylinder temperature is conducive to reducing friction losses, improve fuel economy. The advantage of the split cooling water jacket system is to make the engine work at the best temperature setting point, and achieve the high cooling efficiency. The experimental results show that the flow of cooling fluid temperature of the cylinder head is reduced to 50 DEG C, and the flow of cooling fluid temperature of the cylinder body is 80 DEG C, the compression ratio increased from 9 to 12, can realize the part load condition, saving 7%, saving 5% idle full load power output increased by 10% of the target. Clough M.J. put forward the concept of "precision cooling" as early as 1992, that is, to minimize the cooling to achieve the best temperature distribution. The key is to determine the exact design of cooling system cooling water jacket size, selection of cooling water pump, cooling capacity, ensure the system can meet the engine at low speed and high load of key areas of the working temperature of the demand. The results show that the coolant flow rate can be decreased by 40% in the whole working speed range. The potential advantage of precision cooling is to increase the speed of the machine, reduce the thermal stress and heat loss. The friction coefficient and the power consumption of the cooling water pump can be reduced, and the average effective pressure and the antiknock property can be improved. Clough of a four valve gasoline engine cylinder body and a cylinder cover for transformation, to achieve precise cooling water jacket, the volume is reduced by 64%, the pump power consumption decreased 54%, the warm-up time is reduced by 18%. Whether it is an accurate cooling system or a shunt cooling system, it is necessary to improve the engine cooling water jacket to optimize the flow of coolant. From the point of view of design and application, thecombination of split cooling and precise cooling has a good prospect, which is favorable to the formation of an ideal engine temperature distribution, which meets the requirements of the engine to the future cooling system.At present, the material of thermal management system is relatively single, and the radiator material is usually copper, aluminum and aluminum alloy. The design method of the traditional radiator has reached the limit, so it is urgent to develop a new and efficient cooling concept to improve the cooling performance.Nanofluid nanofluid is a kind of engineering heat transfer fluid, which is formed by dispersing nano metal particles in the traditional heat transfer fluid (water, ethylene glycol mixture and oil). Argonne National Laboratory (Argonne) is developing a nano particle to improve the thermal conductivity of engine coolant and oil. The test results show that the thermal conductivity can be increased by 40%. Leong using nano fluid as the research of engine cooling fluid, the total heat transfer coefficient and the heat transfer rate than base fluid for ethylene glycol has greatly improved, Reynolds number in the air side and the radiator coolant side were 6000 and 5000, copper nanoparticles 2% to enable the heat transfer is enhanced by 3.8%, the estimation of air windward area reduced by 18.7% air radiator. At the same time, the application of nanofluids in the engine cooling system can reduce the size and weight of the cooling system of the heavy-duty vehicle by 10%, so the combustion efficiency of the engine will be increased by 5%. The use of nanofluids can also use a higher temperature of the cooling liquid to reduce heat loss. The application of the high temperature radiator reduces the size of the radiator by 30%, thereby reducing the flow resistance of the air, reducing the flow loss of the cooling fluid and the loss of the driving fan, and saving the fuel consumption by about 10%. Figure 4 shows the thermal conductivity ratios of different nanofluids (metal particles and oxide particles) k/k. (K. The relationship between the thermal conductivity of ethylene glycol and the volume fraction of nanoparticles.Aokeliqi National Laboratory (ORNL-0ak Ridge National graphite foam Laboratory) developed a unique graphite foam, can greatly improve the heat transfer coefficient. The graphite foam density is 0.2 ~ 0.6g/cm fand thermal conductivity is 40-187/m.K. Because the foam honeycomb mesh structure, large contact surface (>4 m /g), radiator made of graphitefoam is the overall heat transfer coefficient will increase more than 10 times than the traditional radiator.Klett and so on with graphite foam made of a 22.9cm x 17.78cm 15.27cm heat exchanger (radiator), installed in the 588kW V8 racing engine, replacing the original 68.6cm x 48.3cm x 7.6cm radiator. Under the condition of the speed of 290km/h, the water temperature is 99.4 degrees Celsius, the cooling water flow rate is only 57.5L/min, the fan air flow is only the original 2.3%. The overall heat transfer coefficient is 10 times higher than that of the traditional radiator. Therefore, the cross-sectional area of 48CM x 69cm car radiator, with the same amount of heat dissipation, the size can be reduced to 20cm x 20cm. This reduces the size, quality, and cost of the radiator, thereby increasing fuel efficiency.发动机热管理系统优化发动机热管理是从系统整体角度，集成控制发动机的燃烧、增压与进排气、冷却系统和发动机舱等的传热，提高循环效率，减低热负荷，控制发动机部件高低温极限、温度分布及其规律变化，在提高发动机的冷却能力的同事，保持发动机良好的动力性、经济性、排放性能和可靠性。