Fuel Film Dynamics in Direct Injection Engines

Direct injection engines deliver fuel at high pressure directly into the combustion chamber. When the fuel spray strikes surfaces such as the piston crown or liner, a thin liquid film forms. This film evolves through spreading, breakup and evaporation, interacting with the in-cylinder air flow to influence fuel–air mixing. Film thickness and coverage determine the rate of vapour formation and entrainment into the combustion core, thereby affecting flame propagation, ignition timing and particulate formation. Key factors controlling film behaviour include injection pressure, spray momentum, surface temperature and fuel thermophysical properties. Experimental methods—such as laser-induced fluorescence, refractive-index-matching and high-speed optical imaging—have revealed the transient, two-dimensional distribution of these films under engine-relevant conditions. Complementary computational fluid dynamics (CFD) models using Lagrangian–Eulerian spray representations coupled with wall-film submodels have deepened understanding of heat and mass transfer at the spray–wall interface. Advances in this field support global efforts to enhance fuel efficiency, reduce pollutant emissions and optimise the use of alternative or blended fuels in modern direct injection powertrains.

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Fuel Film Dynamics in Direct Injection Engines publication trend

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Technical terms

Fuel film: A thin liquid layer deposited on chamber surfaces after spray impingement, which governs local evaporation and mixture formation.

Spray–wall impingement: The event in which fuel droplets impact a surface, leading to film formation, splashing and secondary atomisation.

Evaporation rate: The mass of fuel vapourised per unit area and time from the liquid film, determined by surface temperature and film thickness.

Lagrangian–Eulerian approach: A CFD technique that tracks individual droplets (Lagrangian particles) within a continuous gas phase (Eulerian grid).

Large eddy simulation (LES): A turbulence modelling method that resolves large-scale flow structures while modelling smaller eddies, applied to spray and wall-film interactions.

References

1. Novel method for the measurement of liquid film thickness during fuel spray impingement on surfaces. Optics Express (2016).
2. Experimental and numerical investigation of evaporating fuel films in combustion. Applications in Energy and Combustion Science (2021).
3. Experimental Study on Macroscopic Spray and Fuel Film Characteristics of E40 in a Constant Volume Chamber. Energies (2023).
4. Experimental Study on the Adhesive Fuel Features of Inclined Wall-Impinging Spray at Various Injection Pressure Levels in a Cross-Flow Field. Sustainability (2023).