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Diesel exhaust emission regulations & SCR technology & high accuracy NOx sensors

The exhaust emission gas regulations on truck diesel engines are becoming increasingly stringent in various countries in the coming years.

SCR technology is widely used in diesel exhaust post-treatment, by optimizing the fuel injection and combustion process, as far as possible in the engine to control the generation of particulate PM, and then outside the engine to deal with nitrogen oxides formed under oxygen-rich conditions, timely vehicle urea (vehicle urea decomposition at a certain temperature into ammonia) for selective catalytic reduction of nitrogen oxides (NOx). In order to achieve both energy saving and emission reduction, this technology is the mainstream technical route in Europe, Europe long-distance trucks and large buses almost all adopt this technology.

For such SCR systems to be realized, high precision NOx sensors for carrying out urea injection quantity control and SCR degradation diagnosis are absolutely indispensable.

The NOx concentration is generally detected using a NOx sensor as follows: O2 is emitted using an O2 detection electrode; the remaining NOx is decomposed by a NOx detection electrode; and the NOx concentration is detected by current when oxygen ions are passed through a solid electrolyte. This sensor is ideally suited for the monitoring and control of different kinds of NOx catalysts and for the measurement of raw NOx emission in exhaust systems.

A NOx sensor consists of a probe, connecting harness and driving control module. The probe converts O2 and NOx in the air into basic current signals by electrochemical reaction. The connecting harness has eight built-in cables to connect the probe and the driving control module. The driving control module is responsible for driving the probe and generating the electrical signal in a proper temperature environment, adjusting the electrical signal calibration to the standard value, and outputting the calibrated value to the external interface through the CAN bus.

the key components as below

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