A PRACTICAL FIBER OPTIC AIR-RATIO SENSOR OPERATING BY FLAME COLOR DETECTION

This article discusses the development of a simple fiber-optic sensor used to detect the air-ratio in a premix type gas boiler, by monitorin g and appraising the color of the flame emission, including the effect of radical emissions. Such boilers with a multi-port plate burner sho w an improved thermal efficiency, with the environmentally friendly ef fect of a reduction in both NOx and CO in the exhaust gas. The sensor is used to monitor and maintain the air-ratio in order to enable effec tive feedback control, and a low-cost, durable and small sensor soluti on is presented. Tests carried out show the potential of the sensor fo r use outside the laboratory and image processing techniques are used to analyze the spectral features of the emissions seen to confirm the spectral regions of use of the fiber-optic sensor. (C) 1997 American I nstitute of Physics.