Modelling the Measurement Techniques of the Ion Current in Stagnated Premixed Ammonia-Air Flames

抄録

In order to further investigate the discrepancy between the numerical and experimental outcomes of ion current trends of stagnated ammonia-air flames, the measurement technique of the ion current was altered from the flame being scanned by a single vertically moving cathode probe, to both the anode and the cathode moving in tandem horizontally through the flame. As with the vertically scanning cathode method, horizontal scanning results show that, as the equivalence ratio increases from 0.89 to 1.19, the peak value of ion current generally decreases as progress is made into the rich zone. The horizontal scan technique results in a peak ion current at φ = 1.01, whereas the vertical scanning method gives a peak at φ = 0.95. Elementary reaction calculations performed using an expanded ionic mechanism and the burner-stabilized stagnation flame model, predicts the dominant positive ion NO⁺ to peak at φ = 0.98. Furthermore, the new expanded mechanism predicts the existence of high concentrations of OH^- ions in the burned gasses peaking at φ = 0.95. These negative ions could possibly explain the variance in equivalence ratios where the peak ion current occurs with different measurement techniques. This paper attempts to create a model to explain the phenomena based on these findings. It is concluded that in stagnated ammonia-air flames, and possibly in ammonia-air flames in general, the technique used to measure the ion current must be taken into consideration when used as a diagnostic tool.