| In response to the"Blue Sky Protection Campaign"plan in 2017,the state vigorously promotes the upgrading of environmental protection regulations,and the major diesel engine enterprises are actively responding to the emission of gas pollutants.At present,there are few researches on NO_X emission control of high-power non-road diesel engines in China,and the relevant high-efficiency NO_X emission treatment technologies are not mature enough.However,non-road environmental regulations of China will transition from the third stage to the fourth stage,so it is necessary to study the emission control equipment of high-power non road diesel engine with higher NO_X conversion efficiency in this paper.On the basis of consulting domestic and foreign literature and emission regulations,and understanding the research status at home and abroad,this paper mainly carried out the following work:1.The SCR internal structure and installation layout was designed,and SCR model was simulated.In order to improve the anti crystallization ability and NO_X conversion efficiency of urea SCR system,the urea spray point was placed in the center of the pipeline according to the analysis,and the spray cone angle of urea was 60°.According to diesel engine exhaust gas flow rate and other parameters,the urea mixing pipe is improved and designed.The diameter of the urea mixing pipe is increased from250mm to 300mm.The multi-stage mixer is used in the mixing pipe.The installation mode of 7-row catalyst in parallel is used in the package barrel.According to the different bending direction of urea spray gun and exhaust pipe,four kinds of SCR packaging installation structures are designed.SRAR-CCM+is used to simulate the performance of four SCR structures.It is found that the SCR system has the lowest crystallization risk and the best NO_X conversion performance when the B side of the exhaust pipe is bent and the urea spray gun is installed on the A side.2.The urea injection strategy for SCR was designed.There are many application scenarios of high-power diesel engine studied in this paper.The developed strategy can match different application conditions by calibrating NO_X conversion efficiency.The off-line test of the developed urea injection strategy proves the accuracy of the strategy.The precision of the injection system is tested,and the precision is within±2%,which meets the application needs.3.The crystallization contrast test of SCR system was carried out.A new type of crystallizing bench is designed,in which fans and electric heating equipment are added to change the exhaust gas flow and temperature on the bench,which can verify the anti crystallizing ability of SCR system under different matching conditions.The crystallization test results show that when the exhaust pipe is bent to B side,the urea spray gun is installed on the A side of mixing pipe,the anti crystallization ability of the urea SCR system is stronger,and there is no crystallization under all test conditions,meeting the matching requirements of the diesel engine.4.The performance of SCR urea system was verified and the NO_X conversion performance was tested.The experimental results show that the NO_X conversion efficiency of SCR system is 70.7%and 93.2%respectively under the two calibration efficiencies,and the specific emissions of NO_X after treatment are 2.32g/(kW·h)and0.54g/(kW·h),which are lower than 3.5g/(kW·h)and 0.67g/(kW·h)in the fourth stage of non-road emission regulation. |
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