Engine SCR (Selective Catalytic Reduction) catalyst system and control method thereof

Abstract

The invention discloses an engine SCR (Selective Catalytic Reduction) catalyst system and a control method thereof. The engine SCR catalyst system comprises an engine body, an SCR catalyst and a bypass pipe; a supercharger compressor, an intake pipe, an engine intake manifold and an intake throttling valve are arranged at the intake end of the engine body, and the intake throttling valve is located on the intake pipe; an engine exhaust pipe and a turbocharger turbine are arranged at the exhaust end of the engine body, and an exhaust temperature sensor is arranged on the engine exhaust pipe; an SCR upstream temperature sensor and an SCR downstream temperature sensor are arranged in the upstream and the downstream of the SCR catalyst respectively; the bypass pipe is connected at the front end of an inlet of the SCR catalyst in parallel, and a two-way bypass valve is arranged at an inlet of the bypass pipe. The engine SCR catalyst system can reduce heat loss of the SCR catalyst to the maximum extent, raise or keep temperature of the SCR catalyst and improve the conversion efficiency of the SCR catalyst.

Description

technical field [0001] The invention relates to the field of engine NOx emission reduction, in particular to an engine SCR catalyst system and a control method thereof. Background technique [0002] As the engine reduces NO X An important technology for emissions, SCR (Selective Catalytic Reduction) is widely used in medium and heavy vehicle engines. In the case of a certain hardware configuration such as the SCR catalytic converter coating and carrier, the actual conversion efficiency of the SCR catalytic converter can be improved by increasing its temperature and reducing the exhaust space velocity. [0003] With the increasingly stringent emission regulations, especially for urban vehicles that implement the WHTC emission cycle, in order not to sacrifice too much fuel consumption to ensure emissions, the burden on the SCR catalyst is also increasing. However, for low-horsepower and low-load engines in the WHTC emission cycle area, the temperature of the SCR catalytic co...

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Problems solved by technology

[0005] 1. In reverse dragging condition, the air intake throttle valve cannot be completely closed, and a part of the airflow always flows through the SCR catalytic converter to take away heat; and the exhaust gas from the exhaust pipe to the SCR catalytic converter can be regarded as an adiabatic expansion process. temperature will drop further

[0006] 2. If the opening of the air intake throttle valve is too small, a large negative pressure will be generated in the cylinder during the air intake process, and the oil in the crankcase will flow up, and the insufficiently burned oil will lead to increased particles and smoke

[0007] 3. In the non-emission area, especially in the idling condition, some exhaust gas with very low nitrogen and oxygen and relatively low average temperature TC of the SCR catalyst flows through the SCR catalyst, causing unnecessary heat loss, and this part Exhaust gas flowing through the SCR catalyst for a long time will reduce the ammonia storage continuously, which is not conducive to the improvement of the efficiency of the SCR catalyst

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