MHD & EHD: Combustion in the Presence of Electrohydrodynamics

Description

This project simulates combustion in the presence of an electrohydrodynamic (EHD) field using ANSYS Fluent. A simple combustion chamber is designed, into which airflow and fuel enter axially. The fuel, C₁₀H₂₂ (decane), enters through the central section, with the airflow surrounding it.

The study is carried out in two stages. First, ordinary combustion between air and fuel is investigated; then the same combustion is performed in the presence of an EHD field. Applying EHD causes the fluid to become electrically charged, and the motion of the ionized particles or molecules — together with their interaction with the electric field and the surrounding fluid — is studied. The combustion reaction is modeled using the Species Transport model, with C₁₀H₂₂ and O₂ defined as reactants and CO₂ and H₂O as products.

Airflow enters the chamber at 447 K with a velocity of 5 m/s, while fuel enters at 300 K with a velocity of 0.01 m/s. The EHD model is used to impose the effect of the electric field on the chamber's performance: a current density of 40 A/m² is applied at the inlet and outlet boundaries, with a positive charge defined on the inlet boundary and a negative charge on the outlet boundary.

Geometry & Mesh

The geometry was created as a 3D model in Design Modeler. The computational domain is a horizontal cylindrical combustion chamber; fuel enters through a narrow inner tube, and airflow enters around this tube. Meshing was performed in ANSYS Meshing using an unstructured grid, producing 1,000,658 cells.

Setup & Solution

Several assumptions underpin the simulation: a pressure-based solver is used, the simulation is steady, and the effect of gravity is neglected.

Viscous model — standard k-epsilon with standard wall functions

Species — Species Transport with 5 volumetric species (C₁₀H₂₂, O₂, CO₂, H₂O, N₂) and volumetric reactions

Energy — enabled

Potential (electric field) — enabled

Boundary conditions — Inlet-Air: velocity inlet at 5 m/s, 447 K, O₂ mass fraction 0.21, current density −40 A/m²; Inlet-Fuel: velocity inlet at 0.01 m/s, 300 K, C₁₀H₂₂ mass fraction 1, current density 0 A/m²; Outlet: pressure outlet at 0 Pa gauge, current density 40 A/m²; Inner Wall: stationary, coupled thermal condition; Outer Wall: stationary, zero heat flux, current density 0 A/m²

Methods — Coupled pressure-velocity coupling; second-order for pressure; second-order upwind for momentum, species mass fraction, and energy; first-order upwind for turbulent kinetic energy and turbulent dissipation rate

Initialization — standard method, with 0 Pa gauge pressure, O₂ mass fraction 0.21, velocity 5 m/s, temperature 447 K, and potential 0

Conclusion

On completion of the solution, 2D and 3D contours of temperature, velocity, pressure, and the mass fraction of each species (CO₂, C₁₀H₂₂, O₂, N₂, and H₂O) were obtained. These results are presented in two modes — without EHD and with EHD — so that the effect of the electric field can be assessed through direct comparison.

The contours show that when EHD is applied to the combustion chamber, more energy is delivered to the species, producing higher product temperatures. This rise in the temperature of the reacting species accelerates the combustion reaction. Furthermore, examination of the reaction products indicates that combustion in the presence of EHD proceeds with higher quality, demonstrating how the electric field can be used to enhance combustion performance.