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

Area of Science:

• Optical Engineering
• Internal Combustion Engines
• Spectroscopy

Background:

• Endoscopic optical diagnostics are valuable for internal combustion (IC) engines, preserving engine operating conditions.
• Existing hybrid UV endoscope systems feature expensive relay elements with limited wavelength ranges.

Purpose of the Study:

• To enhance the universal applicability of endoscopic imaging in IC engines.
• To evaluate commercial UV camera lenses as replacements for expensive hybrid relay elements.

Main Methods:

• Replaced the hybrid refractive/diffractive relay element with commercial UV camera lenses.
• Characterized endoscope system performance (resolution, brightness, chromatic aberration) with different lens combinations.
• Utilized unintensified and intensified CCD cameras for evaluation.
• Applied selected imaging systems to a spark-ignition engine for OH* chemiluminescence imaging.

Main Results:

• Endoscope systems with commercial camera lenses demonstrated superior resolution with unintensified CCD cameras at magnifications of 0.5 and 1.
• The original hybrid relay lens system performed best with an intensified camera within its designed wavelength range.
• In-engine imaging results for OH* chemiluminescence correlated well with bench-top characterization.

Conclusions:

• Commercial UV camera lenses offer a viable, cost-effective alternative for endoscopic imaging in IC engines, particularly with unintensified cameras.
• The choice between commercial lenses and hybrid relay elements depends on camera type and specific application requirements.
• Successful in-engine application validates the bench-top characterization and potential of these endoscopic systems.