The nitrogen oxide sensor (NOx sensor) is one of the core components of automobile exhaust emission control. It is mainly used to detect the concentration of nitrogen oxides (NOx) in the exhaust gas, including harmful gases such as NO and NO2. As a key part of the diesel engine SCR (Selective Catalytic Reduction) system, gasoline engine exhaust treatment system, and off - road machinery emission control, its technical principle and performance directly affect the vehicle's ability to meet environmental protection standards.

 

Technical Principle

The nitrogen oxide sensor operates based on the electrochemical principle. Its core element is a porous zirconia (ZrO2) ceramic tube with a platinum electrode coated on its surface. When the sensor probe is exposed to the exhaust gas environment, the combination of the conductivity of oxygen ions in the solid electrolyte (such as yttria - doped zirconia YSZ) and the catalytic performance of the NOx - sensitive electrode promotes the occurrence of an electrochemical reaction. The difference in the NOx concentration in the exhaust gas causes a potential difference between the electrodes, which is then converted into a measurable current signal. The built - in control chip of the sensor processes the current signal into a standard CAN bus digital signal and transmits it to the vehicle's ECU (Electronic Control Unit) to achieve data interaction.

In addition, the sensor is equipped with a dew - point protection function. By delaying the start of detection, it avoids the ceramic element from bursting due to contact with water. The sensor only starts to work when the exhaust pipe temperature reaches the set threshold and remains there for a certain period of time, ensuring that the high - temperature exhaust gas dries the residual moisture and guarantees long - term stability.

 

Core Functions and Roles

1. NOx Concentration Detection: It can accurately measure nitrogen oxides in the concentration range of 0 - 3000 ppm and is compatible with complex exhaust gas conditions such as high oxygen (21%) and high humidity (<12%).

2. Closed - loop Emission Control: Through real - time communication with the ECU via the CAN bus, it adjusts the urea injection volume or the fuel mixture ratio to optimize the efficiency of the SCR system or the three - way catalyst.

3. On - Board Diagnostic (OBD) Support: It continuously monitors the exhaust gas data and triggers fault codes to indicate abnormal emissions, ensuring compliance with strict emission regulations from China IV to China VI.

4. Adaptive Correction Ability: It integrates a storage chip and actively corrects the NOx measurement value through data such as back - pressure parameters and NH3 concentration, reducing the complexity of ECU calibration and development costs.

 

Technical Advantages

- High Sensitivity and Selectivity: It can accurately identify NOx in complex gas compositions and resist interference from CO, HC, etc.

- Fast Response and Stability: It has a short response time, can withstand high temperatures (up to 800°C), and ensures long - term reliable operation.

- Modular Design: The standardized interface is compatible with the diesel and gasoline engine systems of multiple brands, for example, it can be matched with SCR or EGR technical solutions.

 

Application Fields

1. Diesel Vehicle SCR System: It is used in commercial vehicles that meet the emission standards of China IV and above. By injecting urea to reduce NOx, it reduces particulate matter emissions.

2. Gasoline Vehicle Exhaust Treatment: It assists the monitoring of the three - way catalyst, optimizes the air - fuel ratio, and reduces the generation of nitrogen oxides.

3. Off - road Machinery: It is used in the desulfurization and denitrification systems of equipment such as generator sets and construction machinery, contributing to emission control in power plants and industries.

 

Common Faults and Maintenance

- Typical Fault Manifestations: The engine fault light comes on, the vehicle has weak acceleration, the engine idles with a jitter, and the ECU records fault codes such as abnormal NOx signals or dew - point protection failure.

- Maintenance Recommendations: The sensor is usually non - repairable. When it is contaminated by carbon deposits, you can try to clean the probe, but if it is severely aged, it needs to be directly replaced. Avoid contact with moisture or external force damage to the ceramic element during installation.

 

Development Trends

As environmental protection regulations become stricter, the technology of nitrogen oxide sensors continues to be upgraded. The HTCC (High - Temperature Co - fired Ceramic) process improves the heat resistance and signal accuracy of the chip, and the localization process further reduces costs. In the future, the development of intelligent sensors integrating optical detection, wireless transmission, and other technologies will become the focus, driving the innovation of emission control in new - energy vehicles and hybrid systems.