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The role of nitrogen and oxygen sensor in exhaust gas monitoring

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Direct-injection gasoline engines, motorsport applications, and even motorcycles place very specific demands on the technology used for exhaust gas measurement and its aftertreatment, but as you will learn, the engine brings engineers what it takes to “keep it clean” major challenge. Environmental protection In the popularization of automobiles, nitrogen and oxygen sensor technology is particularly important.

Nitric oxide and nitrogen dioxide

To make gasoline engines more economical and environmentally friendly, automakers are increasingly relying on direct gasoline injection engines, which under certain conditions, mainly part load (cruising) conditions, can operate on fairly lean air/fuel mixtures run. The result of this could be a 12-20% reduction in fuel consumption, but as with most things in life, there is a price to pay for this gain.

One of the gaseous compounds produced as a result of the combustion process within an engine during spark ignition is a compound collectively referred to as NOx. For the automotive industry, the term is used to describe nitric oxide and nitrogen dioxide contained in exhaust gas. NOx compounds are environmentally harmful by-products of the combustion process, which are effectively addressed in most vehicles through the function of the three-way catalytic converter.

Spark ignition engines tend to produce more of these compounds when operating on very lean fuel conditions, while direct injection engines operate in this region in stratified mode. Three-way catalysts cannot cope with this problem due to the excess oxygen in the exhaust gas, which reforms NOx and requires additional treatment of the exhaust gas.

NOx gas treatment, automotive gas monitoring

One countermeasure strategy is to use NOx storage catalysts, which are additional hardware installed on the exhaust system that temporarily store and chemically reduce compounds to harmless nitrogen and oxygen at predetermined points. This “regeneration” function is triggered by a change in fueling calibration, resulting in a temporary rich state of fuel within the storage unit.

An important part of the system’s control strategy is the NOx sensor, which is used to detect when the storage capacity (saturation point) limit is reached and then instruct the fuel management system to begin the regeneration phase. The frequency of this cycle may be about once every 60 seconds, then a rich regeneration period begins for about two seconds, and then returns to lean mode.

The NOx sensor is an evolution of the broadband oxygen sensor, the housing of the element is made of stainless steel deep-drawing process, which contains two cooperating oxygen density detection chambers, which can determine the NOx concentration. Their functions are so complex that these sensors require dedicated computer boards that are either integrated into the vehicle’s control module or contained in a unit that is permanently connected to the sensor wiring harness.

It is well known that most spark-ignition vehicles must be equipped with catalyst monitoring diagnostic sensors. However, this may not be the case with NOx sensors.

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