High-speed combustion diagnostics in a rapid compression machine by broadband supercontinuum absorption spectroscopy

Area of Science:

• Spectroscopy
• Combustion Science
• Internal Combustion Engines

Background:

• Supercontinuum absorption spectroscopy offers a non-intrusive method for analyzing combustion processes.
• Accurate measurement of thermodynamic properties like temperature, pressure, and water mole fraction is vital for understanding and optimizing internal combustion engines.
• Previous spectroscopic methods faced limitations in robustness and spectral range for high-temperature combustion environments.

Purpose of the Study:

• To present the first results from a supercontinuum absorption spectrometer under fired internal combustion engine conditions.
• To demonstrate simultaneous inference of temperature, pressure, and water mole fraction using broadband H2O absorbance spectra.
• To enhance the spectrometer's robustness and extend its detectable wavelength range for improved combustion monitoring.

Main Methods:

• Utilized a supercontinuum absorption spectrometer to monitor auto-ignition combustion of n-heptane/air mixtures in a rapid compression machine at 10 kHz.
• Extended the detectable wavelength range to 1340-1440 nm, focusing on the P-branch above 1410 nm for high-temperature water transitions.
• Implemented a strategy to mitigate line-of-sight (LOS) effects by evaluating spectra within a narrower region (1410-1440 nm) to minimize interference from low-temperature molecules.

Main Results:

• Successfully inferred temperature, pressure, and water mole fraction simultaneously during combustion events exceeding 65 bar and 1900 K.
• Demonstrated improved spectrometer robustness against beam steering for combustion measurements.
• Showed that evaluating spectra in the 1410-1440 nm range effectively mitigates LOS effects from cold molecules.

Conclusions:

• The developed supercontinuum absorption spectrometer is robust and effective for in-situ combustion analysis in internal combustion engines.
• The method allows for precise, simultaneous measurement of key combustion parameters under extreme conditions.
• Optimized spectral evaluation strategies are crucial for accurate spectroscopic analysis in complex combustion environments.