Rate Determination of the CO2* Chemiluminescence Reaction CO + O + M = CO2* + M

The use of chemiluminescence measurements to monitor a range of combustion processes has been a popular area of study due to their reliable and cost-effective nature. Electronically excited carbon dioxide (CO2*) is known for its broadband emission, and its detection can lead to valuable information; however, due to its broadband characteristics, CO2* is difficult to isolate experimentally, and the chemical kinetics of this species is not well known. Although numerous works have monitored CO2* chemiluminescence, a full kinetic scheme for the species has yet to be developed.

A series of shock-tube experiments was performed in H2-N2O-CO mixtures highly diluted in argon at conditions where emission from CO2* could be isolated and monitored. These results were used to evaluate the kinetics of CO2*, in particular, the main CO2* formation reaction, CO + O + M CO2* + M (R1). Based on collision theory, the quenching chemistry of CO2* was determined for eleven common collision partners. The final mechanism developed for CO2* consisted of 14 reactions and 13 species. The rate for R1 was determined based on low-pressure experiments performed in two different H2-N2O-CO-Ar mixtures.

Final mechanism predictions were compared with the experimental results at low and high pressures, with good agreement seen at both conditions. Peak CO2* trends with temperature as well as overall CO2* species time histories were both monitored. Comparisons were also made with previous experiments in methane-oxygen mixtures, where there was slight over-prediction of CO2* experimental trends by the mechanism.Experimental results and mechanism predictions were also compared with past literature rates for CO2*, with good agreement for peak CO2* trends, and slight discrepancies in overall CO2* species time histories. Overall, the ability of the CO2* mechanism developed in this work to reproduce a range of experimental trends represents an improvement over existing models.