Matching Study Between Organic Rankine Cycle System And Selective Catalytic Reduction System Used For Vehicle

The increase of automobile has not only aggravated the large-scale consumption of fossil energy,but also caused severe environmental pollution,which is attributed to the low efficiency and worse emission of the engine.Organic Rankine Cycle（ORC）technology and Selective Catalytic Reduction（SCR）technology have been widely studied and exerted,because both of them can effectively alleviate the above two problems of the engine.Since both the ORC system and SCR system are used for the engine exhaust and have strict request for the exhaust temperature and mass flow rate,their performance will be substantially affected by matching order between ORC system and SCR system.Therefore,this article focuses on the matching study between the ORC system and SCR system.Firstly,the engine,ORC system and SCR system simulation model are established based on GT-Suite,and the accuracy of simulation model are verified by experimental data and theoretical calculations,respectively.Then,simulation model is used to study the exhaust waste heat characteristics,Nitrogen Oxides（NOx）emission characteristics,waste heat recovery characteristics of ORC system and NOx emission reduction characteristics of SCR system under engine operating condition.Results show that under engine operating condition,the range of exhaust temperature and mass flow rate are 505-782 K and 30-158 g/s,respectively.The NOx concentration varies in the range of 60-3400 ppm.Both net power output of ORC system and the outlet temperature of evaporator positively correlate with exhaust temperature and mass flow rate,with the variation of 0.009-2.12 k W and 307-457 K,respectively.The NOx conversion efficiency of SCR system is substantially affected by exhaust temperature of engine,and extreme high and low temperature will downgrade its performance.Therefore,it is necessary to cool the engine exhaust through the ORC system before entering the SCR system to avoid the impact of high-temperature exhaust.At the same time,it is necessary to avoid that the performance of SCR system is downgraded due to excess dcrement of exhaust temperature when maximizing the performance of waste heat recovery of ORC system.In order to avoid the adverse effects of the ORC system and the SCR system in the matching process,the operating mode of the ORC system and SCR system under engine operating condition is divided,and the strategy based on the engine exhaust temperature is proposed to control the switch of operating mode.Afterward,the simulation model of ORC-SCR combined system and corresponding control system are established based on GT-Suite and Matlab/Simulink,which is used to compare and analyze the performance of ORC system and SCR system before and after coupling mutually.Results show that the performance of SCR system is substantially improved after coupling with ORC system under engine operating condition,with an average NOx conversion efficiency increment of 11.79% and an maximum increment of 34.57%;the performance of ORC system decreases,with an average waste heat recovery efficiency decrement of 0.67% and a maximum decrement of 1.9%.In order to study the matching characteristics of the ORC system and SCR system under the real road condition,a vehicle simulation model including engine,ORC system,SCR system and control system is established.The vehicle simulation model is used to analyze the operating characteristics of the ORC system and SCR system before and after coupling mutually under UDC road condition and Artemis motorway130 road condition.Results show that the average NOx conversion efficiency of SCR system can be increased by 2.78% after coupling with the ORC system under UDC road condition,while the average waste heat recovery efficiency of ORC system decreases by 0.07%.The average NOx conversion efficiency of SCR system can be increased by 15.56%after coupling with ORC system under the Artemis motorway130 road condition,while the average waste heat recovery efficiency of the ORC system decreases by 1.66%.In summary,the poor performance of SCR system is mainly caused by the low exhaust temperature under urban road condition which consist of low velocity.Therefore,the performance improvement of SCR system after the coupling with ORC system is subtle.Although the performance of ORC system is also affected more slightly,the waste heat recovery efficiency of ORC system is still poor due to low exhaust energy caused by low exhaust temperature and small mass flow rate under low velocity road condition.In contrast,the overall engine exhaust temperature is high and stable under highway road condition which consist of high velocity.Therefore,the performance improvement of the SCR system is manifest after coupling with ORC system.Although the performance of ORC system is affected severly,the waste heat recovery efficiency of ORC system is still more acceptable due to high exhaust energy caused by high exhaust temperature and large mass flow rate under high velocity road condition.Therefore,the combined system coupling ORC system with SCR system should be applied to high velocity road condition with high exhaust temperature and large mass flow rate,while the low velocity road condition with low exhaust temperature and small mass flow rate should be avoided as much as possible.