This work focuses on the use of naturally occurring optical emissions, specifically chemiluminescence, for sensing applications in active control and health monitoring of combustors. First, monitoring local equivalence ratio (φ), at the reaction zone, has been demonstrated using the ratio of CH to OH chemiluminescence. This ratio (CH*/OH*) increases monotonically with equivalence ratio, and the dependence on equivalence ratio has been shown to be a universal function for combustor configurations ranging from unconfined jet flames to swirl and dump stabilized combustors. There is essentially no difference between the CH*/OH* ratio for methane and natural (city) gas, but the ratio has a lower sensitivity to φ for n-heptane compared to methane or natural gas. The ratio was found to increase almost linearly with pressure for natural gas/methane combustion above 3 atm. Second, chemiluminescence emission from the combustor was used to detect precursor events to blowout, using a robust thresholding method. This method was shown to be successful in jet flames and swirl/dump stabilized combustors using premixed methane/air and nonpremixed Jet-A/air. This method gives the kind of information on proximity to blowout that can be used by an active control system to prevent lean blowout in low NOx turbine engine combustors. © by T. M. Muruganandam, B. Kim, R. Olsen, M. Patel, B. Romig and J. Seitzman.