Laminar flame speed provides a metric by which to evaluate chemical kinetics models, which are used to predict the complex behaviors of combustion processes. Historically, the schlieren technique has been used in the spherically expanding, optically tracked flame rig to measure laminar flame speed, but this experimental method only produces laminar flame speed data. Chemiluminescence of intermediate radicals is indicative of the high-temperature reaction zone of the flame, and it can be used to measure laminar flame speed in a similar fashion to the widely used schlieren imaging technique while also measuring other species-specific data to be used for model validation. An experimental study of laminar flame speed of spherically expanding methane-air flames measured from chemiluminescence of OH* at 306 nm and of CH* at 430 nm is presented for the first time. To validate the new diagnostic and compare to existing data in the literature, flame speeds for one atmosphere and room temperature methane-air flames were measured from OH* and CH* chemiluminescence for equivalence ratios from 0.7 to 1.3. There was no significant difference between flame speeds measured from different wavelengths (or species) of chemiluminescence. The new data are in good agreement with data from the literature, indicating that chemiluminescence can be used to extract accurate laminar flame speed measurements from spherically expanding flames. Additionally, a set of experiments was performed that took advantage of the window arrangement of the facility by simultaneously capturing schlieren images and chemiluminescence images of each experiment. This set of flame speed data showed that, within the uncertainty of the chemiluminescence measurements, there was no difference between the flame speed measured using schlieren and that measured using chemiluminescence. Another set of experiments was conducted for mixtures of methane, oxygen, and carbon dioxide in the interest of studying oxy-methane combustion for supercritical carbon dioxide power cycles. These tests showed good agreement with existing data. Future improvements to the chemiluminescence technique can be made, specifically with respect to image quality and noise reduction.
