Urea injection system for reducing NOx discharge of engine and control method thereof

Abstract

The invention discloses a urea injection system for reducing the NOx discharge of an engine. The urea injection system mainly comprises a urea supply unit, an injection unit, an unfreezing unit and a control unit. The urea supply unit comprises a urea unidirectional flow pump, a secondary filter, a first electromagnetic valve and a gas liquid mixer which are sequentially connected with a urea tank by a first pipeline; and a spray nozzle part in the injection unit is used for spraying the gas liquid mixture into an exhaust pipeline communicated with the upstream of an SCR (Selective Catalytic Reduction) catalyst; according to the system disclosed by the invention, urea is sucked out of the urea tank and a certain pressure is formed, the injection quantity of the urea is automatically regulated according to the operation working condition of the engine, and the urea is sprayed into the exhaust pipe of the engine after the urea is atomized by high pressure air so as to react with NOx discharged from the engine on the SCR catalyst, and thus, the aim of reducing the NOx discharge is fulfilled; and the control unit is communicated with an engine controller to coordinate the normal work of the integral system and monitor the working conditions of the system and the parts.

Description

technical field [0001] The invention relates to an engine exhaust purification system, in particular to a urea injection system for reducing engine NOx emissions. Background technique [0002] With the rapid growth of China's automobile production and ownership, the problem of automobile exhaust pollution is becoming more and more serious. In order to deal with this prominent problem, the country has successively issued automobile emission standards and regulations at different stages, and various automobile and engine companies have also gradually adopted automobile engines. Corresponding technical measures have been taken to meet the gradually tightening emission regulations. In terms of diesel engines for heavy-duty vehicles, before and after China III emission standards, internal measures are basically adopted to achieve the goal, such as using high-pressure common rail, increasing fuel injection pressure, precisely controlling fuel injection time and angle, using exhaus...

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Problems solved by technology

[0009] At present, there are vehicle exhaust SCR post-treatment urea injection systems that can meet the above requirements, such as the urea injection system developed by PUREM disclosed in DE102006040411A1, the SCR system of Siemens disclosed in US6209315B1, including the Granite used in the domestic market. Fu company and German Bosch company's systems, some of which use gas-assisted injection, are more ingenious in design and have better atomization effects, but the above are all foreign systems, and the design and manufacturing costs of components are very high, which is not conducive to SCR systems Large-scale promotion in the country

Similar systems have also appeared in China in recent years, including the SCR urea injection system developed by the Wuxi Oil Pump Nozzle Research Institute disclosed in CN101737127A, and the quantitative injection device of Suzhou Paigeli Emission Reduction System Co., Ltd. disclosed in CN101818677A. It is too perfect, but there are some problems. For example, the scheme of thawing with the help of engine exhaust mentioned in the former system is not easy to realize control; The designed passive pressure stabilizing airbag cannot play the role of energy storage when the gas source is turned off, and cannot effectively return when the system is turned off, and there is no thawing measure, which cannot solve the problem of urea freezing at low temperature

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