The Development Of Non-gas-assisted Urea Injector For SCR System

Automobile exhaust emission threatens environmental safety,and in order to protect the air environment,more and more stringent emission regulations have been introduced.Each major diesel engine manufacturer and auto parts manufacturer separately introduce their own tail gas disposal system to meet the requirements of emission regulations.The SCR technology reduces the emissions of pollutants by injecting urea into the exhaust gas and reducing the nitrogen oxides in the tail gas to water and nitrogen.The urea injectors are the key components of SCR system,and it can be divided into air-assisted type and non-air-assisted type.The non-air-assisted urea injector’s system is simple and suitable for vehicle of wide range.This kind of injector is generally consist of the rapid opening and closing mechanism and atomization components.The injector’s working environment temperature is high,and its low pressure atomization performance and injection precision must be good.At present the domestic market mainly occupied by foreign products.In this paper,a non-gas-assisted urea nozzle is developed for domestic diesel engine demand,and the specific work of this paper is as follows.A new structure of urea injector was proposed.The modified maximum flow coefficient method was applied to design the atomization mechanism,and the atomization effect at low pressure was optimized.The basic parameters of the injector’s runner and the influence of the gap flow on the atomization effect is analyzed,and the viscous force of the annular gap on the valve core is calculated.According to the requirement of sealing pressure,the cone valve is designed and calculated,and the contact ratio pressure of the valve seal is checked by APDL simulation.Electromagnet is designed according to the suction demand.Maxwell and Simulink are used to simulate the valve core motion and calculate the valve core response speed.The temperature distribution of the injector was analyzed by Fluent software,and the performance of the electromagnet at rated temperature was checked.A performance test system for urea injector was established,and the atomization performance and control properties of the urea injector were determined.The experimental results show that the flow rate and atomization angle of the urea injector can meet the design requirements,and the average diameter of the particles is the same as that of the Bosch and the Tenneco urea injectors.Under the rated pressure,with the increase of the power time ratio,the flow rate of urea injector increases linearly,and the control performance meets the design requirements.