| With the increasing of vehicle possessing in our country,the exhaust gas pollution problem can't be neglected even more.Because diesel engine has the advantage of high dynamic performance,it is widely used in long-distance transport and other fields.A large amount of nitric oxide is produced during the working process of diesel engine,which can cause acid rain and photochemical smog,so SCR technology,as one of mainstream technology to reduce nitrogen oxide emissions has been widely used at present.During the working process of diesel engine,much noise can also be produced,so the exhaust noise needs to be reduced at the same time of purifying exhaust gas.The normal way to reduce noise is to install muffler after exhaust gas purification device.For the restriction of installation space and the bad influence to engine,exhaust gas purification device and muffler usually can't be used at the same time.So at present a lot of researches have been done on exhaust catalytic muffler which has functions of purifying exhaust gas and reducing noise.In this paper,a detailed research on exhaust catalytic muffler of diesel engine was carried out by means of experiment and numerical simulation.The main work was as follows:(1)Designed and set up the exhaust noise offline simulation test bench and choosing the critical component,such as air blower,flow meter and so on.Then adjusted and replayed the exhaust noise by use of mixer,power amplifier and loudspeaker.Used vibration and noise test equipment to detect the noise characteristic at the outlet.(2)Did the off-line simulation test under cold condition to get the insertion loss of exhaust catalytic muffler with the exhaust noise offline simulation test bench.At the same time used the GT-POWER software to simulating the real condition and got the insertion loss under hot condition.Then compared the two insertion losses as described above to ensure the result from off-line simulation test should be corrected.(3)A detailed research on difference value between insertion loss under hot condition and insertion loss under cold condition for expanding structure and catalyst carrier under different working conditions was carried out by means of experiment and numerical simulation.And then chose some kinds of expanding structure and catalyst carrier with different structure parameters to do the simulating calculation to see if structure parameters had influence on the difference value stated above.The results indicated that under different working conditions insertion losses under hot condition and cold condition for expanding structure were normally the same.That was to say,temperature had almost no influence on noise reduction performance for expanding structure.But for catalyst carrier,different temperatures really had significant influence on insertion loss.The insertion loss got under hot condition was higher than the one got under cold condition.Therefore,the reason why test article had different insertion loss under different temperatures was that the catalyst carrier had different insertion losses under different temperatures.Finally,for the problem described above,used dimensional method to find out three non-dimensional numbers,and then used multivariate fitting software to fit correction formula.After verification,proved the formula to be suitable.(4)For the problem that the insertion loss of the test article couldn't satisfy the request of laws and regulations,optimized the structure to increase the insertion loss.By extending the inlet pipe into the expansion chamber and punching many holes on it to form the perforated pipe,the noise reduction performance on some frequency bands of this test article could be increased.In addition,increased the length of the first expansion chamber to improve the silencing frequency characteristic.At last,by means of software simulation,confirmed that the insertion losses of the optimized structure were all significantly increased under every working condition. |
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