Thick Film Zro2 Nox Sensor for the Measurement of Low Nox Concentration

Document Number: 980170

Date Published: February 1998

Author(s):
Nobuhide Kato - NGK Insulators, Ltd.
Hiroshi Kurachi - NGK Insulators, Ltd.
Yasuhiko Hamada - NGK Insulators, Ltd.

Abstract:
A practical ZrO2 NOx sensor using dual oxygen pumping cells has been introduced for the control of NOx emitted from a lean-burn gasoline engine and diesel engine. However, the mea accuracy was not high enough to be useful for controlling or monitoring a low level of NOx concentration such as several tens ppm behind a three-way catalyst or lean NOx catalyst which is NOx adsorption or De-NOx catalyst.

This paper describes improvement of the interference effect of oxygen in the exhaust gas from the lean-burn gasoline engine and diesel engine. The cause of oxygen dependency is analyzed/revealed and a method of improvement is introduced.

The improved NOx sensor has an approximately \mP2% measuring error in the wide range of oxygen concentration on a model gas system, compared to the \mP10% of the previous one. The improved NOx sensor provides a linear signal with a measuring error within \mP10%, in a diesel engine operating under practical conditions in which oxygen concentration, gas temperature, and back pressure of exhaust gas vary from 2 to 14.5%, 175 to 730\mDC and 2 to 100 mmHg respectively. It is also confirmed that the improved NOx sensor can monitor less than 100 ppm of NOx emitted from a Toyota D-4 engine equipped with a NOx adsorption catalyst. The improved NOx sensor would be capable of measuring less than 100 ppm of NOx behind catalyst.

Therefore, the improved NOx sensor would be useful for OBD of lean NOx catalyst and for control of NOx adsorption catalyst.

File Size: 182K
Product Status: In Stock

See other papers presented at International Congress & Exposition, February 1998, Detroit, MI, USA, Session: Electronic Engine Controls

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