Study On Turbocharged Engine Exhaust Noise Prediction And Reduction Technology

Turbocharged engine was widely used in the automotive and shipbuilding industries,because it can effectively improve the dynamic performance. But, as people's attention to environmental protection, the exhaust noise problem has become one of the problems to be solved in today's society. A simulation modal of SUV turbocharged engine is established by using GT-Power software. The other engine model also was set up after turbocharged engine has checked with the experimental data. This modal has the same speed and load with turbocharger engine to ensure the exhaust noise source of different modals is roughly equal.According to the analysis of flow field and acoustic field exhaust subsystem, this dissertation mainly studied the influence on engine exhaust noise of the turbocharger. Studies have shown that the turbine of the acoustic effect is similar to a quieter element,through the consumption part of the kinetic energy of the exhaust and reflected a part of the sound energy, made the exhaust noise effectively attenuation in the low frequency domain. But it created higher sound pressure amplitude. in the part of high frequency domain because of the eddy current and rotation noise.In order to explore the relationship between the engine structure and the exhaust noise, in this thesis, the injector, the combustion process, ignition timing,exhaust valve,compression ratio and exhaust manifold forms were studied, and found some relation between exhaust noise and the structure of the above. Exhaust noise and combustion pressure in cylinder has a close relationship at exhaust valve opening moment. Pressure pulse of exhaust pipe changed significantly because pressure is relatively higher in cylinder, and it lead to exhaust noise enhanced accordingly. On the premise of improve the power output, structure parameters need to be optimized, to reduce the exhaust noise.Silencer was installed in noise transmission way is the most effective means of noise reduction. In the process of study of silencer, the one dimensional time domain method was compared with three dimensional finite element method,and calculated the transmission loss of four muffler model. The results were analyzed and compared with the experimental data, it verified the one dimension acoustic time domain method in low frequency domain calculation has higher reliability. On this basis, according to the requirements of the muffler design, the appropriate ternary catalytic converters,the former silencer and rear silencer were selected to make up exhaust muffling system, and had a coupling calculation with engine. In view of the exhaust noise spectrum characteristic, two improved schemes for rear muffler were put forward to satisfy the noise reduction target, and choose the optimal solution. Because of the exhaust noise sound pressure level has reached the nonlinear range, this paper also studied the exhaust system acoustic nonlinear analysis.Finally, according to the actual data of the car, a turbocharged engine and the SUV coupling model were established,and calculated the acceleration of the car and by noise. The modal calculated the exhaust noise in common speed(2000r/min),as while analyzed the impact of the transient change of exhaust noise .The load suddenly was increased or decreased when the speed did not change. In addition, the article also calculated the engine exhaust noise when the load is constant,the speed at 2000r/min instantly add or subtract 200r/min.Results show that the speed of turning points, there will be noise peak of exhaust noise in the transient process, and it is higher than the steady state condition.