Combustion Dynamics of Emulsified Fuel Droplets

Emulsified fuel droplets, in which a dispersed phase (often water or a volatile component) is suspended within a continuous hydrocarbon medium, undergo complex combustion events that can enhance atomisation and mixing. The key dynamics include heat transfer to sub-droplets, internal bubble nucleation and growth, and eventual disruptive phenomena such as puffing and micro-explosions. These processes significantly increase the liquid–gas interfacial area, accelerating evaporation and promoting homogeneous mixing of fuel vapour with oxidiser. Puffing is characterised by successive small vapour expulsions, whereas micro-explosions involve violent droplet disintegration into multiple child droplets. The occurrence and intensity of these events are governed by factors such as fuel composition, volatility differentials, droplet size distribution, heating rate and ambient conditions. Understanding these interactions is vital for optimising combustion efficiency, reducing pollutant emissions and advancing next-generation engines and spray-flame technologies. Recent advances in high-speed imaging, direct numerical simulation and theoretical modelling have elucidated the interplay between bubble dynamics, interfacial instabilities and secondary atomisation, paving the way for rational design of emulsified fuels in industrial and environmental applications.

Research from Nature Portfolio

Recent studies have delineated the atomisation mechanisms in multi-component fuel droplets with marked volatility differences. Time-resolved high-speed experiments revealed that vapour bubble formation drives ligament-mediated breakup, with bubble aspect ratio determining whether ligaments undergo mild oscillations or full micro-explosions. In blends with small volatility differentials, micro-explosion arises primarily from bubble expansion, while high differential systems also engage Rayleigh–Taylor instabilities at the vapour–liquid interface. The resulting ligament growth and pinch-off processes were shown to produce narrowly distributed secondary droplet sizes, highlighting how tailored volatility contrasts can be exploited to fine-tune atomisation and combustion performance.

Combustion Dynamics of Emulsified Fuel Droplets publication trend

The graph below shows the total number of articles in combustion dynamics of emulsified fuel droplets across all publications each year (not limited to Nature Index journals).

Technical terms

Emulsified fuel droplet: A liquid droplet comprising a dispersed phase suspended within a continuous fuel phase.

Puffing: Repetitive gentle vapour expulsions from superheated sub-droplets causing minor droplet deformation.

Micro-explosion: Rapid, violent disintegration of a droplet into multiple child droplets due to internal bubble collapse.

Sauter mean diameter (SMD): Diameter of a droplet with a surface-to-volume ratio equal to the ensemble average.

Rayleigh–Taylor instability: Interfacial instability occurring when a lighter fluid accelerates into a denser fluid.

Ohnesorge number (Oh): Dimensionless parameter quantifying the ratio of viscous forces to inertial and surface tension forces.

Ligament-mediated atomisation: Breakup mechanism in which fluid ligaments form and fragment into secondary droplets.

References

1. Atomization characteristics and instabilities in the combustion of multi-component fuel droplets with high volatility differential. Scientific Reports (2017).
2. A computational study of thermally induced secondary atomization in multicomponent droplets. Journal of Fluid Mechanics (2022).
3. Micro-Explosion Phenomenon: Conditions and Benefits. Energies (2022).