In this work, effects of direct-current (DC) electric fields on the flame propagation and combustion characteristics of premixed CH 4 /O 2 /N 2 mixtures were experimentally investigated at excess air ratios of 0.8, 1.0, and 1.2, room temperature, and atmospheric pressure. Results show that the existence of the DC electric fields significantly affects the flame propagation and combustion properties. Specifically, the flame shape becomes a prolate spheroid, with the major axis in the electric field direction as a result of the movement of positive ions by the electric body force, and a further increase in the applied voltage distorts the flame front more significantly. Additionally, the flame propagation speed in the electric field direction (S n ) and corresponding unstretched laminar burning velocity (u l ) are increased as the electric field becomes more intense, and this behavior is more pronounced for lean mixtures. Finally, the initial and main combustion durations defined by the pressure evolution profiles are shortened. The peak pressure and peak rate of pressure rise are increased with the increase of the electric field intensity just for lean mixtures. The observation of the laminar burning velocity and pressure evolution behavior substantiates the potential of the electric field in enhancing lean combustion.

Abstract:In this work, the effects of the electric fields on the flame propagation and combustion characteristics of lean premixed methane-air mixtures were experimentally investigated in a constant volume chamber. Results show that the flame front is remarkably stretched by the applied electric field, the stretched flame propagation velocity and the average flame propagation velocity are all accelerated significantly as the input voltage increases. This indicates that the applied electric field can augment the stretch in flame, and the result is more obvious for leaner mixture. According to the analyses of the combustion pressure variation and the heat release rate, the peak combustion pressure Pmax increases and its appearance time tp is advanced with the increase of the input voltage. For the mixture of λ = 1.6 at the input voltage of −12 kV, Pmax increases by almost 12.3%, and tp is advanced by almost 31.4%, compared to the case of without electric fields. In addition, the normalized mass burning rate and the accumulated mass fraction burned are all enhanced substantially, and the flame development duration and the rapid burning duration are remarkably reduced with the increase of the input voltage, and again, the influence of electric field is more profound for leaner mixtures. The results can be explained by the electric field-induced stretch effects on lean burn methane-air mixture. OPEN ACCESSEnergies 2015, 8 2588

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