Hybrid Endoscopes for Laser-Based Imaging Diagnostics in IC Engines

Laser-based in-cylinder diagnostics are well established in engine research. The requirement of large-scale optical accesses, however, makes the application expensive and time consuming. It furthermore limits the engine operation range to low loads and speeds. We introduce laser excitation and imaging optics with a minimal outer diameter of 10 mm (imaging optic) respectively 9 mm (excitation optics). The imaging optics allow the observation of a 30×30 mm² field with a working distance of 35-42 mm. In order to increase the optical performance diffractive elements are integrated. These elements provide great flexibility for the excitation beam shaping and help to reduce aberrations in the imaging system with a light throughput comparable to imaging setups with standard large-scale UV optics at the same image magnification. We present this miniaturized diagnostic technique based on fuel tracers for measuring fuel density, equivalence ratio and temperature in IC engines. A two-color detection scheme is applied for oxygen concentration measurements in gas jets and a flow-tagging approach for measuring flow velocities is demonstrated. Additionally, chemiluminescence and fuel concentration measurements in a production engine are presented. Finally, first results of an endoscopic LIF-based in-cylinder temperature measurement are shown.