Study On Transient Response Characteristics Of Vehicle Turbocharger

In a typical natural gas engine,only 35%～45%of the fuel energy is converted into useful work output by the crankshaft,while the remaining energy is discharged into the atmosphere as waste heat,resulting in huge energy waste and environmental pollution.ⅥNatural gas engine using equivalent ratio combustion technology leads to high exhaust temperature,high thermal load,causing a series of poor reliability,cooling system design difficulties and other problems.Therefore,the recovery and utilization of the waste heat energy of natural gas engine can not only reduce the reliability problems caused by high temperature overheating of the engine,but also be an effective way to realize automobile energy saving and reduce CO₂emissions.In order to make full use of the waste heat energy of each part of the engine,this paper studies the waste heat recovery system ofⅥnatural gas engine Rankine cycle.This paper takes YC6K13N-50 NationalⅥnatural gas engine as the research object,carries out the heat balance test,studies the distribution law and recovery potential of the engine’s waste heat energy,and provides the basis for the design and selection of the subsequent Rankine cycle system.Abstract:A two-stage organic Rankine cycle system was proposed for the waste heat characteristics ofⅥnatural gas engine with multiple grades and large temperature gradient.The system consisted of high temperature cycle and low temperature cycle.In the high temperature cycle,the waste heat of exhaust gas and EGR exhaust gas were recovered by efficient,stable and difficult decomposed water.The organic working medium with better thermodynamic performance is used to recover the waste heat of cooling water and the condensing heat load of high temperature cycle in order to realize the efficient recovery and utilization of various waste heat.According to the first law of thermodynamics and the second law of thermodynamics,the thermodynamic model of the system is established,and the model is verified to ensure that the calculation program written according to the method is reliable.The rated working conditions of the engine were selected as the starting point of the system design.The influences of different working medium,cycle mode,system operating parameters（high temperature cycle evaporation temperature,high temperature cycle expansion inlet temperature,low temperature cycle evaporation pressure）on the system performance were analyzed.The results show that for each given medium and cycle mode,there is an optimal operating parameter that maximizes the net output work of Rankine cycle system.The net output work of cryogenic cycle using subcritical cycle is higher than that using transcritical cycle.In the subcritical circulating working medium combination,R123 has the highest net output work under the optimal operating parameters,followed by R1233zd,R601a,R245fa,R600 and R600a.In the combination of transcritical circulating working medium,R32 has the highest net output work under the optimal operating parameters,followed by R143a,R404a,R507a,R125a and R218.Total net output work,flow rate of working medium,evaporation pressure,UA value of system and exergic loss of each working medium combination were compared.The comparison results show that the combination of R601a and subcritical cycle is the most suitable for low temperature circulation,which can give good consideration to the system performance and economy.When water and subcritical cycle are used in high temperature cycle,R601a and subcritical cycle are used in low temperature cycle,the inlet temperature of high-temperature cycle expander is 735K,and the evaporation temperature is 520K,the overall performance of the system is optimal.At this point,the maximum net output work of the two-stage cycle was about 74.93k W,the flow of working medium water in the high-temperature cycle was about 0.08kg/s,the flow of working medium R601a in the low-temperature cycle was about 0.82kg/s,the exergic loss of the system was about 79.91k W,and the UA value of the system was about 68.36k W.k^-1.In order to obtain the maximum energy recovery of Rankine cycle waste heat recovery system,five common operating points（1000r/min,1200r/min,1400r/min,1700r/min,2100r/min）under external characteristics were selected for simulation calculation.The calculation results show that the power of the engine with the two-stage organic Rankine cycle system increases gradually with the increase of the speed at full load,and decreases slightly when approaching the maximum speed.When the engine speed is 1700r/min,the maximum power of the modified engine is about 410k W,the power is increased by about 22%,and the thermal efficiency is increased from 38%of the original engine to 46.4%.The outlet temperature of exhaust gas and EGR exhaust gas decreased significantly,with an average decrease of about 400K and 500K,respectively.