Visualization of hydrogen flame by differential imaging in the ultraviolet region

摘要

Hydrogen flame, which emits only in the ultraviolet and infrared regions and is therefore invisible, was visualized by imaging at 309 nm, which corresponds to the peak in the OH emission. The background was imaged simultaneously at 337 nm, where the flame emission is very weak. Both images were obtained using narrowband interference filters of 1.5 nm bandwidth and image intensifiers, and the flame image was extracted from the difference in the intensity of the images at the two wavelengths. A combination of (1) digitization using a threshold intensity level and (2) Gaussian blur were applied to the difference image for rejection of spurious spots which resulted from the grainy appearance of the image obtained by the image intensifier. This method allowed elimination of reflected sunlight. The method was also used to image hydrogen flame using interference filters of 10 nm bandwidth. The flame region was successfully extracted up to a working distance of 30 m under outdoor daylight conditions.