Extended lattice Boltzmann scheme for droplet combustion

Area of Science:

• Computational Fluid Dynamics (CFD)
• Combustion Science
• Multiphase Flow Modeling

Background:

• Existing lattice Boltzmann (LB) models for combustion or phase change are limited to single-phase flows or two-phase flows with constant densities.
• Simulating spray combustion requires models that can handle complex phenomena like phase change and density variations in multiphase systems.

Purpose of the Study:

• To propose a novel two-phase lattice Boltzmann (LB) method for simulating the combustion of liquid fuel droplets.
• To enable the simulation of spray combustion by addressing limitations in current LB models.

Main Methods:

• Developed a two-phase LB scheme incorporating phase change and combustion, accounting for gas-phase density variations.
• Modeled chemical reactions using the Cahn-Hilliard free-energy approach and evaporation via a source term in the continuity equation.
• Applied low-Mach-number approximations to Navier-Stokes and energy equations, including source terms for heat release, density variation, and radiative heat loss.

Main Results:

• Validated the model by simulating the combustion of n-heptane and n-butanol droplets in stagnant air.
• Achieved good agreement between simulated diameter history and flame standoff ratio and existing numerical and experimental data.
• Demonstrated the model's capability to handle density variations and chemical reactions in droplet combustion.

Conclusions:

• The proposed two-phase LB method is a promising approach for accurately modeling liquid fuel droplet combustion.
• This method provides a foundation for future simulations of complex spray combustion phenomena.
• The model successfully integrates phase change, chemical reactions, and density variations within a unified LB framework.