Preliminary Evaluation of NDIR CO_2 Sensors for Bleed Air Monitoring

摘要

The air used to pressurize the cabin in the majority of commercial airliners is provided by the bleed air system which delivers compressed air from the engine. On rare occasions, the bleed air may become contaminated due to oil leaks, de-icing fluid or ingestion of exhaust from other aircraft or equipment. Potentially, the aviation community is interested in using non-dispersive infrared (NDIR) carbon dioxide sensors onboard commercial aircraft as part of a cabin air quality monitoring system. In this study, four commercially available NDIR sensors have been evaluated to determine their suitability for this application. Sensor characteristics of interest include: weight, volume, range, resolution, response time and accuracy of steady-state readings. In addition, the transient response of these sensors is of particular importance because carbon dioxide concentrations are unlikely to reach steady-state values during a potential contamination event. Two methods, flowing gas and gaseous diffusion, were used to characterize response times. The flowing gas method subjected the sensors to step inputs of premixed, certified gases with concentrations ranging from 600 ppmv to 2000 ppmv CO_2 while the diffusion method enabled measurements of concentrations as low as 550 ppmv.