Ammonia injection system and control method thereof

Abstract

The invention discloses an ammonia injection system and a control method thereof. The ammonia injection system comprises an ammonia storage tank, an ammonia supply module, an ammonia regulating valve,an ammonia metering valve, a pressure sensor, a valve seat, an ammonia nozzle and a controller, wherein the ammonia supply module communicates with the ammonia storage tank, and the ammonia supply module is connected with the ammonia regulating valve; ammonia in the ammonia storage tank enters the ammonia metering valve, and the stable ammonia injection pressure is guaranteed by the controller bycontrolling the opening and closing of the ammonia metering valve; and the controller is combined with the ammonia injection pressure to control the opening and closing duration of the ammonia metering valve so as to inject a proper amount of ammonia. According to the ammonia injection system, double valves including the ammonia regulating valve and the ammonia metering valve are controlled by anelectronic control unit (ECU), so that the stable ammonia injection pressure can be guaranteed, thereby realizing the accurate measurement of ammonia and satisfying the CHINA VI emission requirements; the ammonia regulating valve is an electric control switching valve, the structure is simple, the process is mature, the cost is low, and compared with a mechanical pressure regulating valve, the ammonia regulating valve has obvious cost advantages and reliability advantages.

Description

technical field [0001] The invention relates to an ammonia gas injection system and a control method thereof, belonging to the field of post-treatment of diesel engine exhaust. Background technique [0002] With the implementation of the National IV emission regulations for commercial vehicles, the vehicle must be equipped with after-treatment devices for nitrogen oxide (NOx) emissions. [0003] China's medium and heavy-duty diesel engines generally adopt the selective catalytic reduction (SCR) technology route, that is, the standard vehicle urea aqueous solution is injected into the exhaust, and the ammonia gas generated by its decomposition is used for selective catalytic reduction of NOx to generate harmless nitrogen and water. . [0004] The existing SCR reductant supply system takes the urea system as the absolute mainstream, that is, the standard vehicle urea solution (hereinafter referred to as urea solution) is injected into the exhaust of the engine, and the urea s...

AI Technical Summary

Problems solved by technology

However, the urea solution requires an exhaust temperature above 250°C to be fully decomposed into ammonia gas. When it is below 250°C, it is easy to decompose into intermediate products such as biuret and cyanuric acid. These intermediate products are white crystalline objects, which can cause Urea nozzles, exhaust pipes, after-processors, etc. are clogged, which in turn affects engine emissions

At present, with the implementation of the National V regulations, in order to meet the requirements of the WHTC cycle, the injection temperature of the urea system is generally below 200°C, so urea crystallization is prone to occur, and the conversion efficiency of urea is low, making it difficult to meet the emission requirements

There are other obvious disadvantages of urea solution as a reducing agent: it freezes in winter and needs more than half an hour of heating and thawing before it can work normally; The production process needs to consume 3 times ordinary water

However, this technology requires large-scale infrastructure promotion, which is very difficult to implement and will cause great inconvenience to users

The system requires high-power heating, complex structure and high cost

The system needs a pressure stabilizing valve to stabilize the pressure. The cost of the stabilizing valve is high and the structure is complicated.

The system uses a large number of pure mechanical components, and the OBD function is weak

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