Research Projects

Project at a Glance

Project Status: complete

Title: Demonstration of a fast response on-board NOx sensor for heavy-duty diesel vehicles.

Principal Investigator / Author(s): Smith, Jack A

Contractor: Southwest Research Institute

Contract Number: 98-302

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


A literature search, laboratory testing, and a field demonstration were conducted to determine the suitability and performance characteristics of fast response NOx sensors designed for use on heavy-duty diesel vehicles. Results of the literature search indicated that only the NGK Insulators, Ltd. combined NOx/O2 sensor was available and prepared to be evaluated in this program. Four NGK Insulators, Ltd. combined NOx/O2 sensors were tested under steady-state conditions, transient conditions, under the influence of interference gas, and during real world driving conditions in diesel engine exhaust. Results from the diesel engine steady-state tests showed that the sensors were accurate to Ī10 percent of reading from 0-2000 ppm. In addition, the transient characteristics are such that the NOx component of the sensor responds on average 100 to 200 msec after the O2 component of the sensor (which takes approximately 50 msec) responds due to its design. Carbon dioxide, oxygen, and propylene interference gases all have an effect of decreasing the NOx sensor output as the interference gas concentration is increased at a constant exhaust gas NOx level. A steady-state natural gas engine test was also conducted on two of the sensors. The two sensors performed well and can be used in either diesel or natural gas engine exhaust in a research and development program. However, further investigation is required to fully quantify reliability issues and their impact on a production engine control system in long term, heavy-duty, diesel engine emissions control applications. In the present prototype form, the sensors are not suitable for implementation into heavy-duty, diesel engine emissions control systems.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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