Effect of Turbulence on Forced Ignition of Jet-A/Air Mixtures

Abstract

Consistent ignition of reactive mixtures in turbulent conditions continues to be a challenge, particularly for large, multicomponent fuels. Prior work has shown that turbulence can affect ignition parameters such as flame speed, mixture temperature, and minimum ignition energy (MIE). However, these works have primarily considered small, single-component fuels. This work studies the effect of turbulence on forced ignition of jet-A/air mixtures with φ between 0.3 and 0.7. The ignition probability of these mixtures was measured for bulk velocities between 5 and 7 m/s and turbulence intensities between 3% and 9%. A FLIR SC6700 infrared camera was used to measure the radiation intensity emitted by the flame kernels. Increases in turbulence intensity between 3% and 4% cause the probability of ignition to generally increase. This increase is attributed to the negative flame stretch that develops as a result of the turbulence. This observation is significant because it shows that turbulence can facilitate ignition for jet-A/air mixtures. In contrast, increasing turbulence beyond 5% causes ignition probabilities to decrease. This reduction occurs due to the increased role of heat diffusion and the associated reduction in kernel temperature. The sensitivities of ignition behavior to turbulence intensity and fuel chemistry are reasonably captured using the Peclet number. Further agreement in ignition behavior is achieved by considering Pe/TI2. Ignition probability data for two additional fuels were compared using Pe/TI2. Reasonable agreement within a 95% confidence interval was observed for CH4 mixtures but not for C3H8 mixtures.