Fiber Optic Sensors for In-Situ Monitoring of Diesel Engine Exhaust Gas

Abstract

<p>A fiber optic carbon dioxide sensing system was developed for in-situ monitoring of carbon dioxide within a diesel engine exhaust environment. The fib er sensor was based upon the encapsulation of pyranine paired with tetraoctylammonium hydroxide within a hydrophobic glass formed using the sol-gel process. The sensitivity of the sensor to carbon dioxide was shown to follow a non linear trend with the highest sensitivity in the 0 - 5% CO₂ range. The lower detection limit was experimentally determined to be better than 0.3 % CO₂ . The fiber sensor's response was also characterized within an environment similar to that within an diesel engine exhaust stream. The fiber sensor was shown to be relatively unaffected by carbon monoxide and nitric oxide at concentrations which are typically found within a diesel engine exhaust gas. Nitrogen Dioxide, however, caused an effect in biasing the sensor response to erroneously report higher concentrations of carbon dioxide than were present . Higher concent rations of nitrogen dioxide were shown to permanently damage the fiber sensor and render it inoperative. The effects of increased environmental temperature and relative humidity were shown to decrease the sensitivity of the fiber sensor within the range of interest tor carbon dioxide sensing within diesel exhaust gases. An experiment within the exhaust stream of a single cylinder 2.4 kW diesel engine demonstrated that the fiber sensor was capable of monitoring the carbon dioxide levels for 6 minutes, however, longer exposure to this exhaust environment caused the destruction of the fiber.</p>