| Exhaust gas recirculation(EGR)is a technology that can effectively reduce the NO_x emission of engine,but it has a negative impact on the engine power and fuel economy.For an engine,only the matched EGR system can effectively achieve energy saving and emission reduction.EGR cooler is the critical component of EGR system.Therefore,this paper takes the EGR cooler of off-road diesel engine as the research object,and it has important engineering application value to design it.The paper built the simulation model of ISME380 30 off-road diesel engine on GT-POWER software firstly.Based on this model,the effects of EGR rates and EGR temperatures on power performance,fuel economy and emission of diesel engine were studied at different rotating speeds(1200r/min?1400r/min?1600r/min?1800r/min?1900r/min)and load rates(20%?40%?60%?80%).Considering engine performance and emission limits,the EGR rates and EGR temperatures under various simulation conditions were optimized,and the MAP was drawn.The results show that,after optimization,the NO_x emission rate of the disesl engine can meet the national stage fourth emission limit of off-road disesl engines.The design of EGR cooler with small volume,high efficiency of heat exchange and easy to manufacture is an important prerequisite for the implementation of EGR Technology.In this paper,according to the optimized EGR system operating parameters,the maximum heat load operating point of EGR cooler was obtained by calculation.And this operating point was taken as the design goal of the cooler.Through the combination of structural design and thermal design,the structural form and size parameters of the cooler were designed and the structural parameters of the shell-and-tube cooler were finally determined.According to the calculated structural parameters of the cooler,the models of straight tube,bow baffle plate,bellows and screwed tube coolers were established.Then taking the maximum heat exchange condition of EGR cooler as the boundary condition,the temperature field,velocity field and pressure field of those four coolers were studied by numerical simulation on ANSYS CFX software.The simulation results show that the heat transfer performance of the cooler can be improved more by using the heat exchanger with grooves than by adding baffles in the shell side,and the shape of the grooves also has a great influence on the heat transfer performance.Among the four coolers in this paper,the heat transfer performance of the screwed tube cooler is the best.Its heat transfer efficiency is 11.4%higher than the straight tube cooler.The outlet temperature of the exhaust gas is reduced to 424K and the outlet temperature of the coolant is 365K.It can meet the heat transfer demands under the maximum heat load condition.In addition,the fluid velocity in the shell side of the screwed tube cooler is high and the high temperature area is small,so its reliability and service life are better than the other three coolers.Through the comparison of comprehensive performance,the screwed tube cooler was determined as the EGR cooler of the engine. |
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