Research On Technology Of Waste Heat Recovery Based On The Rankine Cycle

Since the beginning of the21st century, the energy crisis and environmental issueshave become increasingly prominent, making people pay more and more attention to theimprovement of new energy development and energy efficiency. In the modern industry,seen by the energy balance of the internal combustion engine, the external output of usefulwork accounted for only25%~45%of the total energy released in the combustion of thefuel, while the rest is eliminated by exhaust releasing of the cooling system and the engine.Thus, the energy has not been fully utilized. If the power and thermal efficiency of internalcombustion engines in the process of energy releasing from gas emission is increased,energy efficiency can be improved significantly. Rankine cycle waste heat recoverytechnology has been widely used in the recovery of industrial waste heat due to its highenergy efficiency and good adaptability. As to the automotive industry, the Rankine cycleenergy recovery technology has great potential for development.Firstly, this thesis investigate on the thermal parameters of the engine exhaust andthrough thermodynamic properties and its proportion of the exhaust gas components, derivecalculation formula of the thermal parameters of the exhaust gas mixture which facilitatesthe calculation and analysis of the heat transfer process. Thermal equilibrium analysis of CA6DL heavy-duty diesel engines which is the research object makes it clear that the engineexhaust energy accounted for about28%to30%of the total fuel energy; taking into accountthe quality of exhaust gas energy, from exhaust heat available conversion potential estimatesbased on energy analysis we can conclude that the maximum convertible available energyaccounted for about40%of the exhaust energy. The analysis results show that the waste heatof high temperature exhaust of the engine has great value of recycling.Secondly, through theoretical Rankine cycle thermodynamic analysis and study on theimpact of the working fluid nature of the Rankine cycle on the performance of the Rankinecycle, set the selection criteria of the Rankine cycle working fluid. Then the law of influenceof operating parameters on the performance parameters of the Rankine cycle is analyzed byEngineering equation solving software (EES) the preparation of the general program,combined with the working fluid thermal parameters. The variation rule of water and organic fluid cycle under various cycle parameters such as different vapor pressure and condensedpressure on cycle system efficiency are discussed respectivelyAgain, ascertain the Rankine cycle working fluid is the organic fluid R123bycomparison analysis, and thus determine the operating parameters of the system. Conductdesign calculations of structural parameters of Rankine cycle components with theirrespective design manual and analyze the performance parameters of the designed system bythermodynamic calculation. The results show that under calibration conditions, energyrecovered from the Rankine cycle system reached11.9kW. In the event this part of energy isconverted into engine power output, there will be an increase of about10.1%in overallthermal efficiency of engine, an increase4.6%in power, and a decrease of4.4%in fuelconsumption.Lastly, use GT-POWER software to set the simulation model of the engine and theRankine cycle system and by comparing the simulation with the experimental data theaccuracy of the model can be verified, which means it can be used for simulation. Simulationresults show that with the installation of the Rankine cycle system, the total power of theengine is improved up to6.4%, the exhaust temperature is decreased significantly. Under thehigh-speed and high-load conditions, the Rankine cycle system thermal efficiency can reachup to13%. While under low-speed and low-load conditions, exhaust energy results in lowefficiency of the waste heat recovery system. This thesis set forth that by changing theworking fluid flow and other measures to improve the efficiency of the Rankine cycle underlow-speed and low-oad conditions. The simulation results show that the improved Rankinecycle efficiency is improved in the full range of operating conditions.In summary, since the Rankine cycle waste heat recovery system can effectively recoverengine exhaust heat, improve the thermal efficiency while reducing CO2emissions, it is avery promising technology roadmap to achieve vehicles energy saving.