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Release: April 3, 1996


NGK (President: Masaharu Shibata, Head office: Nagoya) developed a NOx sensor for vehicle exhaust gas. The technique, to create a thick film zirconia used in an automotive oxygen sensor, is applied to the NOx sensor.

This development responds to the lean-burn and diesel engine management, both of which have been sophisticated for the purpose of less fuel consumption in the future.

Measuring NOx concentration of exhaust gas by the newly developed NOx sensor, made it possible for the lean-burn and diesel engines to operate most effectively; as a result, NOx emission was reduced.

NGK read the technical paper regarding a NOx Sensor at SAE, held in Detroit in February, 1996. The NOx sensor, as a leading product for the pollution-free vehicle development in the future, created a sensation more than expected especially among the automotive manufacturers. NGK, at this time, makes every possible effort to create a prototype.

Background and Effect

In response to the demand for less fuel consumption by gas engines, the burning technique for lean-burn engines has been actively developed. However, in general, as the engine is lean-burned, more NOx is emitted. To solve this problem, NOx catalyst also has been developed.

NOx is adsorbed and stored on NOx catalyst, and it is deoxidated by the surplus gas. The NOx, which exceeds the capacity of the catalyst, can be found in the exhaust gas. Therefore, if the surplus gas is used when the NOx sensor recognizes NOx in the exhaust gas, the maximum result of NOx deoxidation is obtained; in other words, the surplus gas does not have to be used in vain. NOx sensor plays an important role not only to obtain maximum NOx deoxidation but also not to waste the surplus gas.

On the other hand, for a vehicle with a diesel engine, the relationship between NOx emission and unburned carbon emission is trade-off, which means if NOx emission is reduced, unburned carbon emission is increased. By using a NOx sensor, it becomes possible to maintain NOx emission at the most regulated level and keep unburned carbon emission as little as possible.

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