Flash Boiling Spray Dynamics in Direct Injection Engines

Flash boiling occurs when liquid fuel under high pressure enters an environment whose pressure lies below the liquid’s saturation pressure, driving rapid vapour nucleation and explosive atomisation. In direct injection engines, finely atomised droplets enhance fuel–air mixing, promoting more uniform combustion and reduced emissions. However, under certain superheat conditions, rapid vapour growth can induce spray collapse, in which interacting vapour jets and local shock structures cause plume contraction and droplet coalescence. The onset and progression of flash boiling depend on fuel volatility, injector geometry and in-cylinder thermodynamic state. Experimental diagnostics, including high-speed imaging and tomography, reveal plume–plume interactions and recirculation zones, while computational methods—ranging from Eulerian–Lagrangian solvers to large-eddy simulation—capture phase change, droplet breakup and shock interactions. Advances in real-fluid models and dimensionless characterisations of superheat ratio now allow predictive control of spray morphology across a wide range of injection pressures, nozzle designs and alternative fuel chemistries. A detailed understanding of flash-boiling dynamics is critical to optimising mixture formation in modern spark-ignited engines and emerging high-volatility fuels.

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Flash Boiling Spray Dynamics in Direct Injection Engines publication trend

The graph below shows the total number of articles in flash boiling spray dynamics in direct injection engines across all publications each year (not limited to Nature Index journals).

Technical terms

Flash boiling: Rapid vapour generation when a liquid is injected into an environment below its saturation pressure, leading to explosive atomisation.

Superheat ratio: Dimensionless measure of liquid temperature above its saturation point relative to ambient pressure.

Spray collapse: Inward contraction of a spray plume caused by interacting vapour jets and shock structures, often reducing droplet dispersion.

Lagrangian particle tracking: Computational method that follows individual droplets or parcels through the flow field to model atomisation and phase change.

References

1. Numerical modelling of fuel spray formation and collapse from multi-hole injectors under flash-boiling conditions. Fuel (2018).
2. Numerical Investigation of Spray Collapse in GDI with OpenFOAM. Fluids (2021).
3. Numerical Analysis of GDI Flash Boiling Sprays Using Different Fuels. Energies (2021).
4. Liquid Propane Injection in Flash-Boiling Conditions. Energies (2021).
5. A real-fluid low-dissipative solver for flash boiling simulations of non-equilibrium mixtures. International Journal of Heat and Mass Transfer (2024).
6. Advances in Liquid Atomization via Flash Boiling—A Global Overview. Energies (2023).