An investigation on the droplet characteristics of ethanol in small-scale combustors with two different systems was conducted experimentally and theoretically. The classical capillary-mesh electrode arrangement was applied in Type A electrospray system, and for Type B, an additional ring electrode is included. The droplet size and velocity were measured by a Phase Doppler Anemometer. The electric filed intensity was theoretically calculated in the two electrospray systems. Compared with Type A, Type B system has smaller droplet size and velocity in the same spraying mode. Meanwhile the electrospray process in Type B system is more stable than that in Type A with its smaller root mean square velocity. By measuring the spraying current, the average specific charge of the droplets for the two systems was obtained in different spraying modes. And it was found that the addition of the ring electrode can help to increase the droplet charge, which is the fundamental reason for Type B electrospray system to perform better. The corona charge of the droplets was theoretically calculated for the two electrospray systems. It was found that the calculated specific charge generated by corona charging was in good agreement with the experimental results.
A small ethanol diffusion flame exhibited interesting characteristics under a DC electric field. A numerical study has been performed to elucidate the experimental observations. The flow velocity, chemical reaction rate, species mass fraction distribution, flame deformation and temperature of the flame in the applied DC electric field were considered. The results show that the applied electric field changes the flame characteristics mainly due to the body forces acting on charged particles in the electric field. The charged particles are accelerated in the applied electric field, resulting in the flow velocity increase. The effects on the species distribution are also discussed. It was found that the applied electric field promotes the fuel/oxidizer mixing, thereby enhancing the combustion process and leading to higher flame temperature. Flame becomes shorter with applied electric field and its deformation is related to the electric field strength. The study showed that it is feasible to use an applied DC electric field to control combustion and flame in small-scale.
The aim of this work is to investigate the effects of direct-current electric fields on the behavior of the small-scale diffusion ethanol flame. The flow rate of liquid ethanol, the flame temperatures, and the flame shapes were measured. The results showed that the stable working ranges of a small-scale combustor became narrower under the direct-current electric field. The main reason was that the evaporation velocity of liquid ethanol limited by great heat loss effect cannot keep up with the increasing of combustion velocity by the ionic wind effect. The movements of those charged particles in flame enhanced the combustion process, resulting in higher flame temperatures under positive or negative directcurrent electric field. The flame heights decreased with increasing applied voltages, due to the ionic wind effect increasing the flame temperature and the diffusivity. The flame voltage-current characteristic was also examined. Three regions can be divided: the subsaturation region, the saturation region, and the supersaturation region. Finally, the ratios of electric active power to actual burning thermal power of ethanol flame were calculated. It can be inferred that using the external direct-current electric field with little power consumption to control combustion and flame is a feasible method.
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