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Technical Paper

Thick Film ZrO2 NOx Sensor for the Measurement of Low NOx Concentration

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.(1),(2). However, the measuring 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 · · 2% measuring error in the wide range of oxygen concentration on a model gas system, compared to the · ·10% of the previous one.
Technical Paper

Thermal Reliability and Performance Improvement of Close-Coupled Catalytic Converter

This paper proposes a high temperature catalytic converter design using a ceramic substrate and intumescent matting. It also describes the improvement of converter performance using an advanced thin wall ceramic substrate. Due to future tightening of emission regulations and improvement of fuel economy, higher exhaust gas temperatures are suggested. Therefore, reduction of thermal reliability of an intumescent mat will be a concern because the catalytic converter will be exposed to high temperatures. For this reason, a new design converter has been developed using a dual cone structure for both the inlet and outlet cones. This minimizes heat conduction through the cone and decreases the temperature affecting the mat area. This design converter, without the use of a heat-shield, reduces the converter surface temperature to 441°C despite a catalyst bed temperature of 1050°C. The long term durability of the converter is demonstrated by the hot vibration test.