Diffuse-light two-dimensional line-of-sight attenuation for soot concentration measurements

Area of Science:

• Optical Physics
• Combustion Science
• Spectroscopy

Background:

• Accurate transmissivity measurements are crucial for characterizing particulate media and flames.
• Traditional methods like collimated 2D-LOSA can suffer from beam steering interference.
• High sensitivity is required to detect subtle changes in optical thickness.

Purpose of the Study:

• To introduce and validate a diffuse-light two-dimensional line-of-sight attenuation (diffuse 2D-LOSA) technique.
• To demonstrate its high sensitivity and improved noise rejection capabilities.
• To compare its performance against collimated 2D-LOSA in flame studies.

Main Methods:

• Utilized an optical system with an arc lamp and integrating sphere for diffuse light.
• Imaged diffuse light to the center of the particulate medium and then to a CCD detector (1:1 magnification).
• Performed comparative measurements in nonpremixed methane-air flames (weakly sooting and high pressure).

Main Results:

• Diffuse 2D-LOSA achieved very high sensitivity, measuring optical thicknesses down to 0.001.
• The technique effectively mitigated interferences from beam steering.
• Comparative tests showed improved optical noise rejection over collimated 2D-LOSA.
• Sensitivity was primarily limited by the shot noise of the lamp and CCD detector.

Conclusions:

• Diffuse 2D-LOSA is a highly sensitive and robust technique for transmissivity measurements.
• It offers significant advantages in noise reduction compared to collimated methods.
• The technique is well-suited for analyzing complex environments like flames and particulate-laden flows.