The Research On The Influence Of Sequential Turbocharging Combined With EGR On The Performance Of A Yacht Engine

With the depletion of petroleum resources and the increasingly stringent emission restriction regulations,requirements for working performance and emission of yacht engines are becoming higher.In order to effectively improve the poor performance of yacht engine at low load and reduce the emission of polluted gases from yacht engine,this thesis chooses sequential turbocharging technology and EGR technology,researches the effect of sequential turbocharging combined with EGR technology on the performance of yacht engine based on TBD234V6 diesel engine.?1?The simulation model of TBD234V6 diesel engine is established by GT-power software based on the data of engine structure parameters and initial boundary conditions.The accuracy of the simulation model is verified by comparing the power,torque,maximum burst pressure and fuel consumption rate in the simulation calculation with the experimental data.?2?The original turbocharging system of TBD234V6 diesel engine was transformed into a sequential turbocharging system and an external high pressure EGR system with venturi tube was installed,propulsion characteristic test is carried out on the test platform after the completion of the refit,by comparing and analyzing the test data with the original data,the effects of successive turbocharging combined with different EGR rates on the performance of yacht engines under different loads were studied,the results show that:When no exhaust gas is introduced,the sequential turbocharging system works separately,compared with the original machine,the engine's low-load power and economy are optimized,the emission of NO_X and soot is reduced;the performance of the engine at medium and high loads is slightly reduced.After the introduction of the exhaust gas,the engine's NO_X emission decreases as the EGR rate increases,but the maximum combustion pressure in the cylinder decreases,the fuel consumption rate increases,the engine power and economy deteriorate.?3?A multi-objective optimization decision-making model based on grey theory is established,the test data are substituted into the model,the comprehensive optimization effect values corresponding to different EGR rates are calculated to determine the optimal EGR rates under different loads of sequential turbocharging combined with EGR engines.The results show that:The optimum EGR rate is 0.03 at 25%load,compared with the original machine,the maximum combustion pressure in the cylinder increases by 0.73 MPa,the fuel consumption rate decreases by 6.9 g/kW·h,and the NOx emission decreases by 249 ppm,the smoke decreases by0.061m^-1,the poor performance of yacht engine under low load is optimized;the optimal EGR rates for 50%,75%and 100%loads are 0.09,0.12 and 0.12 respectively,at this time,at the cost of a small reduction in power and economy,engine NOx emissions are reduced by 26.9%,34.7%and 38.2%compared with the original engine respectively.?4?Transforming the original simulation engine model into a simulation model of sequential turbocharging combined with EGR and verifying the accuracy of the model.Take25%load,EGR rate 0.03;50%load,EGR rate 0.09;75%load,EGR rate 0.12 as research operating point,by adjusting the compression ratio in the simulation model,the influence of compression ratio on the performance of yacht engine is studied and the optimum compression ratio is determined.Based on the optimal compression ratio,further study the effect of injection advance angle on engine performance and determine the optimal injection advance angle.The results show that:The optimal compression ratio of the 25%,50%,and 75%load corresponding to the operating point is 15.5.Based on the optimal compression ratio,the optimal injection advance angles for each operating point are 25°CA,26°CA,27°CA respectively.The performance of the engine is further improved by optimizing the compression ratio and the fuel injection advance angle of the sequential turbocharging combined with the EGR engine.