Characterization of different endoscopic imaging systems in ultraviolet range for combustion applications

Endoscopic optical diagnostics for IC engines offer the advantage of retaining the full operating range and thermal properties of the production engine. The custom-designed modular hybrid UV endoscope system is optimized for application in IC engines.; however, its hybrid refractive/diffractive relay element is expensive and has a narrow operating wavelength range. To make the endoscopic imaging more universally applicable, the hybrid relay element of the mentioned endoscope system was replaced by commercial UV camera lenses, and several combinations were characterized in terms of resolution, brightness, and chromatic aberration. With an unintensified CCD camera, endoscope systems using commercial camera lenses had better resolution at investigated magnifications of 0.5 and 1. However, with an intensified camera, the system with the hybrid relay lens had the best overall performance in its design wavelength range. Selected imaging systems were used in a spark-ignition engine to image O H ^∗-chemiluminescence, with results consistent with those from bench-top characterization.