Diesel Injection: High Pressure, Penetration Length

Diesel Injection at High Pressure, Penetration Length Analysis

Description

This project simulates diesel injection at high pressure (500 bar) under an elevated environmental pressure (10 bar), analyzing the diesel spray's penetration length and jet angle — both critical parameters for optimizing combustion efficiency and reducing emissions in diesel engines. A two-way Discrete Phase Model (DPM) captures the interaction between diesel droplets and the surrounding air, with results visualized through animations and plots of velocity, pressure, and droplet diameter at multiple time steps.

The geometry of the diesel injector and combustion chamber was built in SpaceClaim, accurately representing the nozzle and spray region. The domain was meshed 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

The simulation was configured to handle multiphase flow dynamics, capturing the interaction between the discrete diesel droplet phase and the continuous air phase through a two-way coupled DPM, accounting for momentum and energy exchange between the two phases. Turbulence was resolved using the Realizable k-epsilon model, chosen for its robustness and accuracy in high-Reynolds-number turbulent flows relevant to droplet mixing and dispersion.

Boundary conditions included an injection pressure of 500 bar — ensuring fine fuel atomization and improved air mixing — and an environmental (chamber) pressure of 10 bar, representative of real diesel combustion chamber conditions. Diesel fuel was modeled with a density of 830 kg/m³ and a viscosity of 2.7 mPa·s. Injection was simulated using pressure swirl atomizers, a configuration widely used in diesel engines to achieve fine, uniform spray distribution.

Conclusion

The penetration length results show an initial rapid increase, consistent with the high 500 bar injection pressure, followed by a slower increase and eventual stabilization as the spray droplets undergo atomization and dispersion — behavior shaped by turbulence, droplet size, and environmental pressure. These trends offer a useful basis for evaluating and refining pressure swirl atomizer design to achieve desired spray characteristics under specific operating conditions.

Velocity contours show peak velocity concentrated near the nozzle exit, decreasing as the spray propagates into the chamber, while pressure contours reveal a high-pressure region near the nozzle that dissipates as the spray expands outward. Droplet diameter remained small under the 500 bar injection condition, indicating effective atomization — a key factor for efficient combustion and reduced emissions. Accompanying animations capture the spray's transient development, including vortex formation and the ongoing interaction between droplets and the surrounding air.