Measurement of Carbon Monoxide (CO) in Sooting Flames Using Femtosecond Two-Photon Laser-Induced Fluorescence (fs-TPLIF)

摘要

Incomplete oxidation and soot formation in hydrocarbon flames can produce highly toxic colorless, odorless gas, carbon monoxide (CO), which also has a major role in ground-level ozone formation. In-situ, non-intrusive measurement strategies are crucial for understanding CO and soot formation pathways and to develop advance combustion concepts by minimizing partial oxidation and maximizing the energy release from hydrocarbon fuels. The objective of this work was to apply the recently demonstrated, femtosecond-laser-based, two-photon laser-induced fluorescence (fs-TPLIF) technique to measure CO concentrations in a series of sooting flames. The results show interference from photolytically produced C_2 Swan-band emission have a pronounced effect on CO fluorescence signal under fuel-rich combustion conditions, while interference of C_2 originating from soot could be avoided almost completely by using a narrower detection gate. Comparison of the measured CO fluorescence signal with the calculated CO number density shows good agreement for both premixed laminar CH_4/air and C_2H_4/air flames for a wide range of equivalence ratios. These results indicate that through the use of low-average power but high-peak-intensity, fs-duration excitation pulses in TPLIF of CO, photodissociation of excited carbon dioxide (CO_2) can be evidently reduced in fuel-rich flames. Such measurements can also provide that the fs-duration excitation pulses have potential in high-repetition-rate CO imaging measurements in sooting flames.