Carbon-monoxide (CO) Real Time Monitoring in Combustion Engines by an Optical Detection System

The experimental characterization of an innovative optical system for detection of carbon monoxide (CO) is reported. In this system a photodetector based on gallium nitride (GaN) and an UV light source are integrated. The gas flows between the light source and the GaN photodetector. The UV light source consists of a spark produced by an arc discharge which induced transitions in the gas, causing a modification of the light intensity as a function of gas composition. These transitions modify the fraction of light in the UV spectral region which is detected by the GaN-photodetector, as a function of the species concentration. By virtue of its structural properties, gallium nitride (GaN) allows to operate at high temperature and high speed and to work in-situ in the exhaust manifold of combustion engines at temperatures as high as 600degC, at which the deposited organic residuals on the detector can be oxidized. This assures the clear surface needed for a real time optical measurement of the species concentration to be used for a closed loop control of the fuel injection process. The system was applied to the detection of CO with concentration between 0-2.4% in a buffer of pure nitrogen gas, showing an increase in the measured photocurrent as a function of the above gases