Particle Surface Reaction in Diesel Fuel Combustion

Diesel Fuel Combustion: Particle Surface Reaction CFD Simulation

Description

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

The primary objective is to analyze the behavior of the reacting spray, track the spatial distribution of species such as CO₂ and H₂O vapor, and evaluate how evaporation and reaction kinetics influence overall combustion efficiency. The study combines finite-rate chemistry with the eddy-dissipation model to capture both kinetically-controlled and turbulence-driven reaction dynamics, offering insight into the spatial distribution of combustion products that can help optimize diesel combustion for efficiency and emissions control.

ANSYS Fluent solves this reacting multiphase flow using an Eulerian-Lagrangian approach: the continuous gas phase is modeled through the Navier-Stokes equations coupled with turbulence and combustion models, while the discrete diesel droplet phase is tracked using the Lagrangian framework. The geometry of the diesel injector and combustion chamber was built in SpaceClaim to accurately capture the nozzle and spray region, and the mesh was generated in ANSYS Meshing with refinement concentrated near the injector nozzle to resolve the high velocity and pressure gradients occurring there. The final mesh totals 1,250,256 cells, balancing computational accuracy with efficiency.

Methodology

Diesel droplets were injected and tracked as discrete particles using the Discrete Phase Model, undergoing evaporation and chemical reaction as they traveled through the domain. Since the fuel was modeled as a mixture of gasoil and water, multicomponent evaporation was applied: water evaporates first due to its lower boiling point, while the gasoil component undergoes thermal decomposition and combustion afterward.

Combustion itself was captured using a combined finite-rate/eddy-dissipation approach, accounting for both kinetically-controlled and turbulence-driven reaction behavior to ensure realistic predictions within the turbulent flow field. The Species Transport model solved the transport equations for the reacting species (O₂, CO₂, H₂O vapor) to determine their spatial distribution, while turbulence was resolved using the standard k-epsilon model.

Conclusion

The results include contour plots of the key combustion products and particle behavior throughout the domain. The CO₂ distribution highlights the regions where combustion is occurring and reflects the efficiency of the oxidation reactions taking place, while the liquid water distribution indicates areas of incomplete evaporation or residual water content remaining in the fuel. The H₂O vapor distribution, by contrast, shows the extent of evaporation and combustion product formation across the domain.

Particle diameter distribution shows diesel droplets shrinking as evaporation and combustion progress, with larger droplets persisting in cooler, lower-turbulence regions, while particle temperature profiles show droplet temperatures rising as they move through the combustion zone, peaking near regions of the most intense oxidation activity. Together, these results characterize the spray combustion process in detail and highlight opportunities for optimizing fuel-air mixing and overall combustion efficiency.