Liquid Fuel in a Combustion Chamber: DPM

Liquid Fuel Combustion Inside a Chamber Using DPM

Description

Liquid fuel combustion processes have been at the core of energy production and propulsion systems for over a century, providing the necessary thrust and power for a wide range of applications. Among the various fuel types, liquid ethanol (C₂H₅OH) has gained attention as a renewable and cleaner-burning alternative to fossil fuels, and when paired with an oxidizer such as nitrous oxide (N₂O), it can undergo a vigorous combustion reaction that releases energy for various industrial and technological applications.

This project models that ethanol-nitrous oxide combustion process using ANSYS Fluent, with the geometry designed in SpaceClaim. The combustion chamber measures 6000 mm in diameter, featuring a fuel nozzle positioned at its center. The domain was meshed in ANSYS Meshing, generating a total of 769,000 elements.

Methodology

The liquid fuel droplets were modeled using a two-way Discrete Phase Model (DPM), with the continuous phase solved under steady-state conditions while the discrete phase was tracked unsteadily to capture droplet behavior over time. Turbulence was resolved using the standard k-epsilon model, while the combustion of ethanol and nitrous oxide was captured using the Species Transport model with its volumetric reaction option, coupled with the Eddy-Dissipation turbulent-chemistry interaction model.

Conclusion

The simulation proceeded in two major stages. First, the continuous phase was solved, allowing the velocity and pressure fields to reach steady conditions, with the chamber's average temperature settling at 320 K while filled with nitrous oxide. Once this steady state was established, fuel injection began: ethanol droplets measuring 0.5 mm were injected at a temperature of 273.15 K.

As the fuel droplets absorbed heat from the surrounding environment, their temperature rose over time until reaching the devolatilization point, at which ethanol vapor was released and given the opportunity to mix with the nitrous oxide oxidizer and react. This reaction drove a dramatic temperature rise, with the chamber's average temperature climbing to approximately 460 K, while producing combustion products according to the following reaction:

3C₂H₅OH + 2N₂O → 3CO₂ + 4H₂O + 2N₂