Femtosecond Laser Electronic Excitation Tagging, FLEET, for Combustion and Flow

Femtosecond Laser Electronic Excitation Tagging, known as FLEET, can be used to measure the nitrogen gas content within a gaseous mixture. FLEET does not require any trace particles that could affect the combustion reaction or physical properties of the flow. Another advantage is the simple experimental implementation. In this work a 120-femtosecond laser pulse was focused in to the probe volume to dissociate the nitrogen gas via multiphoton process. The intensity of the light emitted after the recombination is proportional to the nitrogen gas to oxygen mass ratio as the dissociated nitrogen bonds with oxygen to form nitric oxide and other reactions, which does not emit light. Intensity of the light from FLEET within a methane-air diffusion flame was used to determine fuel/air ratio.. The intensity of FLEET signal was calibrated for different mixtures in test cell in the ranges of pressures to simulate the change of number density due to increase of the temperature in the flame.