Evaluation of an UV Analyzer for NOX Vehicle Emission Measurement 2001-01-0213

Chemiluminescense detectors (CLD) represent well-established instruments to measure the concentrations of the oxides of nitrogen (NO_x) in raw as well as diluted automotive exhaust in accordance with the regulations in the United States of America and the European Community. Although the CLD offers the benefits of wide measuring ranges down to low concentrations with a fast response time, its drawbacks are characterized by quenching effects caused by carbon dioxide and water, by an adverse cost-benefit ratio, by the fact that ozone, a highly toxic gas, is necessary for operation, and by additional components needed, such as vacuum pumps and deozonizer. As a consequence, car manufacturers and agencies are looking for alternative analyzers for the measurement of NO in raw exhaust gas. Ultra-violet (UV) analyzers have potential to replace the CLD, as they offer advantages like low noise, no water and CO₂ interference, less equipment for operation and reduced costs.

This paper presents investigations on a new UV-analyzer for analysis of NOx and its potential for the detection of other compounds.

A detailed comparison of NOx measurements operating on an UV-spectroscopy based analyzer parallel to a standard CLD device is given. The experiments are performed under realistic conditions on an engine- and chassis test cell at various applications. Long-run data on t90-times, drift, repeatability, etc are presented and discussed. Moreover, both instruments have been tested at both, steady state and transient tests. A discussion of the respective data is presented and the correlation is analyzed. Additionally the analyzer specifications are determined and compared against the CLD device.