Diesel Fuel Combustion: Particle Surface Reaction CFD Simulation

Simulation of Particle Surface Reactions in Diesel Injection Using ANSYS Fluent

Description

Diesel Spray involves complex multiphase interactions, including liquid fuel atomization, vaporization, turbulent mixing, and chemical reactions. This study employs a Discrete Phase Model (DPM) to simulate diesel spray combustion, where diesel fuel droplets evaporate, react with oxygen, and produce combustion products. The Diesel Spray simulation considers a multi-component diesel mixture, primarily composed of gasoil and water (H2O), injected into an oxidizing environment containing O2. The reaction process leads to the formation of CO2 and H2O vapor.

The main objective of this study is to analyze the behavior of the reacting spray, track the distribution of species such as CO2 and H2O vapor, and evaluate the influence of evaporation and reaction kinetics on combustion efficiency. The study combines the finite-rate chemistry and eddy dissipation models to capture kinetic-controlled and turbulence-driven reaction dynamics. The results provide insight into the spatial distribution of combustion products and can aid in optimizing diesel combustion for efficiency and emission control.

ANSYS Fluent is utilized to solve the reacting multiphase flow using the Eulerian-Lagrangian approach. The continuous phase (gas phase) is modeled using the Navier-Stokes equations with turbulence and combustion models, while the discrete phase (diesel droplets) is tracked using the Lagrangian framework.

The geometry of the diesel injector and combustion chamber was created in  SpaceClaim, ensuring an accurate representation of the nozzle and spray region.

The  mesh was generated using ANSYS Meshing. It focused on refining the region near the injector nozzle to capture the high gradients in velocity and pressure. The final mesh comprises 1,250,256 cells, balancing computational accuracy and efficiency.

Methodology

Computational Approach

• Discrete Phase Model (DPM): Diesel droplets are injected and tracked as discrete particles that undergo evaporation and chemical reactions.
• Multicomponent Evaporation: The fuel is modeled as a mixture of gasoil and water. Water evaporates first due to its lower boiling point, while gasoline undergoes thermal decomposition and combustion.
• Finite-Rate/Eddy Dissipation Model: This approach accounts for both kinetic-controlled and turbulence-driven reactions, ensuring realistic predictions of combustion in turbulent flows.
• Species Transport Model: The transport equations for reacting species (O2, CO2, H2O vapor) are solved to determine their spatial distribution.
• Turbulence Model: The standard k-epsilon model is applied to capture turbulence effects in the reacting flow field.

Results 

The simulation results include contour plots of key combustion products:

• CO2 Distribution: The CO2 contour plot shows the regions where combustion occurs and highlights the efficiency of oxidation reactions.
• H2O (Liquid) Distribution: The liquid water droplets indicate incomplete evaporation or residual water content in the fuel.
• H2O (Vapor) Distribution: The H2O vapor contour plot shows the extent of water evaporation and combustion product formation.

• Particle Diameter Distribution: The size of diesel droplets decreases as evaporation and combustion progress, with larger droplets persisting in regions of lower temperature and turbulence.
• Particle Temperature Profile: Droplet temperatures increase as they move through the combustion zone, with peak temperatures occurring near regions of intense oxidation reactions.

These results provide insight into the spray combustion process and highlight areas for optimizing fuel-air mixing and combustion efficiency.