Flash-Boiling Atomization of Liquid Ammonia: Influence of the Nozzle Aspect Ratio and Injection Conditions on Steady-State Spray Morphology

Energy & Fuels, vol. 40, pp. 16121–16137

Abstract

High Resolution Image Download MS PowerPoint Slide Optimized mixture formation is critical to overcome the combustion-averse properties of ammonia (NH 3 ) in carbon-free energy systems. This study investigates the steady-state flash-boiling atomization of liquid ammonia in stainless-steel micronozzles ( D = 100 μm), linking internal flow mechanics to macroscopic spray morphology. By integrating high-speed shadowgraphy and in-line mass flow measurements with high-resolution μ-CT characterization, we demonstrate that internal manufacturing defects such as nearly planar inlets and localized roughness act as dominant heterogeneous nucleation sites that override idealized CAD predictions. A key finding is the identification of a stochastic regime bifurcation unique to the ultrashort nozzle ( L / D = 1.53), which alternates between non-flashing liquid jets and fully flashing plumes under identical thermo-hydraulic conditions. In contrast, longer nozzles ( L / D ≥ 4.21) remain hydraulically locked in stable flashing regimes. Furthermore, localized nozzle-tip condensation is shown to produce peripheral droplets that may compromise flame stability. By providing a comprehensive data set that links the hydraulic characterization and μ-CT scans of the nozzle internal geometry with spray dynamics, this work establishes a high-fidelity empirical foundation for the development of predictive numerical models and computational fluid dynamics simulations in ammonia-fueled injection systems.

Authors 12

1. Peter W. Augustin corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   Institute of Heat and Mass Transfer

   RWTH Aachen University

2. Marvin Alt Aachen

   RWTH Aachen University

   Affiliation as printed

   Institute of Heat and Mass Transfer

   RWTH Aachen University

3. Lukas Heine Aachen

   RWTH Aachen University

   Affiliation as printed

   Institute of Heat and Mass Transfer

   RWTH Aachen University

4. Reinhold Kneer Aachen

   RWTH Aachen University

   Affiliation as printed

   Institute of Heat and Mass Transfer

   RWTH Aachen University

5. Wilko Rohlfs Aachen

   RWTH Aachen University

   Affiliation as printed

   Institute of Heat and Mass Transfer

   RWTH Aachen University

6. Henry Axt Aachen

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology

   RWTH Aachen University

7. Martin Kratz Aachen Fraunhofer Institute for Laser Technology ILT

   RWTH Aachen University · Fraunhofer Institute for Laser Technology

   Affiliation as printed

   Chair for Laser Technology

   Fraunhofer Institute for Laser Technology ILT

   RWTH Aachen University

8. Christian Hinke Aachen

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology

   RWTH Aachen University

9. Constantin Häfner Aachen

   RWTH Aachen University · Fraunhofer-Gesellschaft

   Affiliation as printed

   Fraunhofer-Gesellschaft e.V

   RWTH Aachen University

10. Fabian Fröde Aachen

    RWTH Aachen University

    Affiliation as printed

    Institute for Combustion Technology

    RWTH Aachen University

11. Heinz G. Pitsch Aachen

    RWTH Aachen University

    Affiliation as printed

    Institute for Combustion Technology

    RWTH Aachen University

12. Manuel Armin Reddemann Aachen

    RWTH Aachen University

    Affiliation as printed

    Institute of Heat and Mass Transfer

    RWTH Aachen University