The state of a flame in a subject combustor of a gas turbine engine is acoustically monitored using a dynamic pressure sensor within the subject combustor and one or more additional sensors in nearby combustors. Dynamic pressure sensor output signals from the sensors are cross correlated to identify acoustic oscillations generated by a flame in the subject combustor and received by the sensors. The cross correlation may be constrained by a maximum time delay between correlated components of the signals, based on physical characteristics.

A combustion assembly for a gas turbine engine includes a combustor, a monochromator, and a photodetector assembly. The combustor forms a combustion chamber. The monochromator is disposed outside the combustion chamber. The monochromator is configured to receive an optical input from the combustion chamber and direct an optical output. The optical input has a range of light wavelengths. The optical output has a subset of the range of light wavelengths. The photodetector assembly is disposed outside the combustion chamber. The photodetector assembly is configured to receive the optical output from the monochromator and generate an output signal representative of one or more optical characteristics of the optical output.

An oven appliance includes a cabinet and a chamber defined within the cabinet for receipt of food items for cooking. A gas burner is positioned in the cabinet, and a first temperature sensor is positioned proximate the gas burner. A second temperature sensor is distal from the first temperature sensor and the gas burner. The second temperature sensor is positioned and configured to measure a temperature in the chamber. A controller is positioned within the cabinet. The controller is configured for measuring a first temperature with the first temperature sensor, measuring a second temperature with the second temperature sensor, calculating a difference between the first temperature and the second temperature, and determining a flame is emanating from the gas burner in response to a positive difference between the first temperature and the second temperature.