The application of spectrum analysis in the visible wavelength region of a large flame was studied theoretically and experimentally. Theoretical study of a flame model, which has a temperature distribution with some variations of optical thickness, indicated that the apparent mean emissivity of continuum emission, calculated on a hypothesis of gray approximation, was applicable to large industrial flames to evaluate flame conditions. An experimental study using a large (12 MW) oil flame also supported the appropriateness of the theoretical study and the apparent mean emissivity was evaluated to correlation well with NOx emissions corresponding to the various kinds of flame conditions.
