Control of Soot Formation in Laminar Flames by Magnetic Fields and Acoustic Waves

To limit global warming a wide set of emission control techniques is required. Here, emission and flame stability control by magnetic fields and acoustic forcing is investigated experimentally and numerically, addressing the example of oxyfuel combustion and black carbon (soot) formation. First, the CIAO in-house code's ability to predict soot volume fraction fields using detailed chemistry and the Hybrid Method of Moments is assessed in a steady coflow flame. Then, pulsating sooting flames at 20 and 40 Hz were studied. Conclusions on the coupling of flow forcing, flame temperature, and peak soot volume fraction are drawn. The magnetic field impact on soot formation was first studied experimentally in steady, coflowing, laminar, non-premixed and partially premixed flames. A magnetic scaling of soot production similar to the known scaling with oxygen was documented for the non-premixed flames. For certain conditions, a trend reversal could be observed in the partially premixed fames. Furthermore, it is shown experimentally and reproduced computationally that a magnetic field gradient can stabilize a spontaneously oscillating non-premixed flame. A local inviscid stability analysis based on the results of the direct numerical simulation is presented for the observed flame to investigate the flame response to small perturbations of the mean velocity, temperature, fuel and oxygen mass fraction under magnetic field exposure. The magnetic field is found to reduce the perturbations' spatial growth rates. The study is completed by identifying a domain within naturally oscillating flames can be stabilized and controlled by magnetic field gradients.