Dynamic Simulation And Optimization Of Rankine Cycle System For Vehicle Based On Drive Cycle

Energy saving and emission reduction is a long-term concern in today’s social development.Making a profound study on vehicle energy saving technology to reduce fuel consumption is an important aspect of promoting energy saving and emission reduction.At present,the thermal efficiency of automotive gasoline engine is between 30%to 40%,a lot of fuel energy is lost in the form of heat via exhaust gas.Researching on exhaust heat recovery is of great significance in vehicle energy saving.Rankine cycle has a good application prospect in vehicle waste heat recovery.The Rankine cycle system for vehicle and its control system are designed based on driving cycle,and optimized by special optimization algorithm.The main achievements are as follows:（1）Based on the modeling of a light-weight passenger vehicle,combined with engine MAP data and exhaust waste heat calculation,the exhaust waste heat characteristics of the vehicle in driving cycle and all conditions are analyzed.（2）Combined with the analysis results,the vehicle Rankine cycle system is preliminary designed and optimized in terms of system structure,components,and working fluid.Also,the corresponding thermodynamic model is established.（3）The control system for Rankine cycle system is designed in order to improve the system response speed and waste heat recovery performance under driving cycle.（4）According to the characteristics and optimization requirements of Rankine cycle system,a special optimization algorithm is designed based on Particle Swam Optimization algorithm（PSO）,the system parameters are optimized by the special optimization algorithm,and the performance of the optimization results and special optimization algorithm is evaluated.The main results are as follows:（1）Under Worldwide harmonized Light vehicles Test driving Cycle（WLTC）,the average exhaust temperature of the vehicle and exhaust mass flow are 983 K and 0.016 kg?s^-1,respectively,which show the characteristics of high temperature and low mass flow.Such characteristics are beneficial to improve thermal efficiency of the Rankine cycle system.（2）The maximum net power of simple Rankine cycle system with R744and spiral tube heat exchanger is 3.187 k W,with an average of 0.327 k W.The average net power drop to 0.258 k W under the limitation of exhaust acid dew point temperature,which decreased by 21.1%.It shows that exhaust acid dew point temperature has a significant limitation on the system.When the system starts up,the maximum net power is minus 1.676 k W with a long system boost time of 18.32 s,which shows that system response speed is slow.（3）After regulated by the mass flow control system with pre-pressurized expander inlet pressure control,the response time of the Rankine cycle system is reduced to 0.20s,which is significantly improved compared with that of the non-control system.（4）After optimization by special optimization algorithm,the maximum net power of Rankine cycle system is 2.260 k W,with an average of 0.269 k W under the limitation of exhaust acid dew point.Compared with original system,the maximum net power decreases by 29.1%,and the average value increases by 4.2%.The maximum net power during system start up is minus 0.778 k W,with a decrease of 53.6%,revealing the optimization results is immensely satisfying.The average fuel consumption of the vehicle with optimized Rankine cycle system is8.33 L?100km^-1 under WLTC driving cycle,which is 2.1%less than that of original vehicle.