Feedback Combustion Control using Chemi-ionization Current 1

The present work demonstrates feasibility of feedback combustion control using a chemiionization current sensor placed in the combustion product flow. The experiments have been conducted in a small-scale combustor followed by a M=3 nozzle. Two electrodes placed in a supersonic flow downstream of the combustor, with a voltage bias applied to them, have been used to measure chemi-ionization current in the flow. Results of previous chemi-ionization current and flame emission measurements demonstrated that the current can be used as a flame indicator. The present experiments show that in lean fuel-oxidizer mixtures, the current is nearly proportional to the equivalence ratio. Chemi-ionization current signal from the combustion product flow have been used for feedback combustion control, to maintain the equivalence ratio in the combustor at the desired level and adjust it, if necessary. In particular, chemi-ionization current was used to control an actuator valve in the fuel delivery line and to vary the fuel mass flow rate. This approach has also been used to counter external perturbations used to deliberately change the equivalence ratio in the combustor. The results suggest that the present method can be used to operate a combustor at fuel lean conditions and to prevent flame extinction by increasing the fuel flow rate before the blow-off occurs. This approach can be used to develop a simple and straightforward combustion control technique.

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