Effects of Electrostatic Voltage and Polarity on Diffusion-Controlled Propane Flame for Enhanced Efficiency

In this study, the direct current (DC) electric field effect on the diffusion-swirling flame dynamics and flame temperature profiles was investigated experimentally with the aim of establishing the feasibility of electric control of combustion in controlling the heat transfer rate and NOx formation. It was observed that with an increase in voltage and change in polarity, the flame configuration, such as shape, size, and length, changes as a result of drastic change in temperature profile for the fuel lean case along the combustor length. Although air flow was turbulent, generating an irregularly dynamic flame, the applied voltage and polarity made the temperature profile more uniform throughout the combustor. Consequently, it was observed that the applied electric field played a vital role in manipulating the flame significantly in terms of flame shape, size, temperature distribution, and flame behavior. Hence by varying the applied voltage from 0 to 2 kV with positive and negative polarities, a field-enhanced reduction in flame temperature was obtained due to increased convective heat transfer to the cooling water, which finally led to lowering thermal NOx formation during the fuel combustion. In the current experimental case the maximum NOx reduction was approximately 30%. A clear difference in sooting behavior was also observed depending on the polarity. While the soot particles accumulated on the injector base away from the positive electrode, they stuck to the negative electrode.