Fast-Response Zirconia Sensor-Based Instrument for Measurement of the Air/Fuel Ratio of Combustion Exhaust

A fast-response zirconia sensor-based instrument has been developed to measure the air/fuel ratio (A/F) of combustion exhaust. This instrument uses a reduced-pressure sampling system which improves instrument response time (due to faster diffusion at lower pressures) and eliminates the need for a heated sample line. The measured response time of the described instrument is 170 ms (0-90%) for a step-change in O₂ concentration. The prototype instrument is easily calibrated in less than 2 min, requiring only nitrogen and room air for calibration. A complete description of the instrument is given. Results of tests comparing the instrument accuracy to a chemical balance technique are given. Also, a comparison study was conducted with the prototype instrument and a conventional zirconia sensor-based A/F monitor (Lamdascan, Sensors, Inc., Ann Arbor, Mich.) with respect to accuracy and response time.