Scale-down of a cyclonic flow field under MILD combustion

The growing need to transition from carbon-based fuels to cleaner alternatives, driven by climate change, necessitates advanced combustion technologies capable of fuel flexibility and low pollutant emissions. MILD combustion is a promising technology that meets these requirements. This work presents the methodology and process for scaling down a reactor with a cyclonic flow field operating under MILD combustion. In such reactors, fluid dynamics play a crucial role due to the recirculation of flue gases, which dilute the air-fuel mixture and preheat fresh reactants. Maintaining similar fluid dynamic behavior during scaling is essential. The scaling process began with designing the new burner. Various configurations were tested, modifying the inlet diameter, nozzle-to-wall distance, and chamber height to preserve residence time. Non-reactive CFD simulations were conducted to analyze velocity fields and select the optimal design. Velocity profiles were examined along the jet injection axis and at the centerline parallel and perpendicular to the jet injection. The selected design maintained the original geometric aspect ratio while varying the nozzle-to-wall distance to avoid wall-jet effects. The scaled reactor, constructed from vermiculite, was experimentally tested under the same conditions as the original. Temperature measurements at three positions showed similar trends and values between the two reactors. Species production also exhibited comparable trends, with slight differences in O2, CO2, and CO concentrations attributed to reduced residence time in the scaled version. NO emissions remained low but showed distinct behaviors due to differences in feeding configurations and formation mechanisms. The comparable temperature distributions and species concentration behaviors between the original and scaled reactors validate the proposed scaling methodology as a reliable approach for adapting cyclonic flow field reactors for MILD combustion.