Measurement of Carbon Monoxide (CO) in sooting flames using femtosecond two-photon laser-induced fluorescence (fs-TPLIF)
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2017 Eastern States Section of the Combustion Institute. All rights reserved. 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 C2 Swan-band emission have a pronounced effect on CO fluorescence signal under fuel-rich combustion conditions, while interference of C2 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 CH4/air and C2H4/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 (CO2) 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.
