Study On The Performance Of A New Type Of Exhaust Muffler For Agricultural Diesel Engine Considering Temperature

As the heart of agricultural machinery,diesel engine not only provides power for the process of agricultural modernization,but also brings noise,which causes harm to the physical and mental health of workers and the environment.In this case,the use of the muffler is particularly important.A muffler with both aerodynamic performance and acoustic performance has become the common goal we pursue.However,in the process of research and design,the diesel exhaust with characteristic of high temperature is often not taken into account,which leads to the muffler cannot achieve the desired effect in the actual operation.In this thesis,a new coupling muffler is designed for the exhaust noise characteristics of agricultural diesel engine,and its comprehensive performance is studied under the condition of considering the temperature factor.(1)Structure design of new muffler based on orthogonal test.The exhaust noise spectrum of CG25 single cylinder diesel engine at idle speed,medium speed and rated speed was measured.A new type of exhaust muffler coupled based on orthogonal test in series by the shunt hedging unit and other resistance units is designed to obtain the low frequency noise within 500 Hz as the target noise reduction target.(2)Fluent software was used to verify the aerodynamic performance of the muffler in the temperature field.The inlet air temperature of the new muffler is 357 K,409K and452 K at idle speed,medium speed and rated speed,respectively.The temperature field,density field,velocity field,pressure field and turbulent kinetic energy field inside the muffler at these three temperatures were calculated respectively in Fluent.The influence law of temperature on the density field and flow field in the muffler is discussed.Temperature often affects the characteristics of flow field by affecting the density.With the increase of temperature,the density decreases,the value of pressure loss decreases,and the velocity field and turbulent kinetic energy field hardly change.(3)The transmission loss of muffler under temperature field was studied by using the software of LMS.Virtual.Lab.The acoustic software LMS Virtual.Lab and Fluent were used to conduct joint simulation,respectively calculating the transmission loss curves of the new muffler at the temperature fields of 357 K,409K and 452 K,and the influence law of temperature factors on the acoustic performance of the muffler was obtained: With the increase of temperature,the muffler noise attenuation peak moves to high frequency,and the arch area of transmission loss curve becomes wider.(4)Comprehensive performance test verification of new muffler.The pressure loss and outlet airflow velocity of the new muffler and the original muffler at normal temperature were tested on the test bench.The pressure loss and outlet airflow velocity of the new muffler were reduced by 25.4% and 20.0%,respectively.The insertion loss of the new muffler and the original muffler in three operating conditions was compared in the real vehicle test.The results show that the insertion loss of the new muffler in various operating conditions is significantly increased.Especially in the rated operating conditions,the insertion loss in the target muffler frequency band of 500 Hz is increased by 5.48 d B compared with the original muffler,and the insertion loss at the noise peak is increased by13.57 d B.The aerodynamics and acoustics of the new muffler are optimized and the expected design goal is achieved.