Turbo-compound Diesel Engine Working Process Simulation And Power Turbine Flow Field Analysis

The problem of vehicle energy saving and the emission regulation are becoming moreand more strictly. Turbocharger technology becomes an important means of engine energysaving. However, the universal existences of conventional turbocharged engine are torqueshortage in low-speed condition, poor fuel economy at part load, as well as poor start-up andacceleration, high emission temperature.The new turbo-compound engine, which combines bypass and complementarycombustion system and the power turbine, not only can improve torque characteristics andacceleration of the engine in low-speed condition, but also can meet the differentrequirements of high and low power in different conditions. The power turbine of theturbo-compound engine can fully utilize exhaust energy which is recovered as effective powerto output, thus improving the total power and the total efficiency of the engine.This paper studies the performance of the turbo-compound diesel engine by numericalsimulation method, focusing two combined-cycle schemes including series and parallel of theturbo-compound diesel engine on the high-power mode. Without changing the structuralparameters of diesel engine, these two schemes meet the needs of the original diesel enginepower density, and the study of flow distribution law and power distribution law is helpful tomaximize the output power of the power turbine, providing theoretical guidance for the benchtest.This paper uses one-dimensional simulation software GT-POWER to analysis the overallperformance and parameter matching calculation, and uses three-dimensional CFDcalculation software to do the detailed simulation of critical components, the parameters ofinlet and outlet obtained from one-dimensional simulation as boundary conditions ofthree-dimensional simulation model. First, the use of GT-POWER software is to build originalturbocharged diesel engine simulation model, including the cylinder model, the injector model,the crankcase model, the intercooler model, the intake and exhaust pipe model and the turbocharger model. Comparing the simulation results and the original experimental data,check and prove accuracy of the model. Adding bypass and complementary combustionsystem and power turbine on the basis of the original engine, we establish series schememodel and parallel scheme model of the turbo-compound combined-cycle diesel engine. Thesimulation results of these two schemes at the rated condition (speed2100r/min) show theparameter variation among the corresponding pressure ratio, expansion ratio, flow, powerturbine power, turbine power, the total output power etc. Based on the optimization analysisof the results after comparing the advantages and disadvantages between two schemes, thispaper proposes the best solution.The results show that the presence of optimal power turbine output power on both seriesand parallel schemes. Series scheme has advantage over the parallel scheme as a whole,greatly improving the total power output. However, this scheme was carried out in the idealcondition of small exhaust back pressure. The actual series scheme is likely to increaseexhaust back pressure, which affects the combustion. The inlet temperature of power turbinereaches1085.34K, turbine inlet temperature of turbocharger reaches1228.45K. Therequirements for high temperature turbine materials need to consider the actual turbinetemperature limits.Aiming at the critical components, the paper uses CFX fluid simulation software toanalysis the flow field of power turbine on three-dimensional steady state, further inspectingand correcting one-dimensional simulation results. The results show that power turbine bladeleading edge and the trailing edge exist large energy loss. In order to improve the thermalefficiency of the power turbine, thereby increasing the output power of the power turbine,partial design of blade shape is unreasonable that need to further optimize.