Flash boiling spray has exhibited remarkable atomization performance by utilizing
the sudden alterations in the thermodynamic state of the fluid during injection.
The notable evaporation properties of flash boiling spray provide potential
remedies for the problem of fuel film adhesion resulting from spray-wall
impingement, especially during cold starts in reciprocating engines. Multi-hole
injectors, which are often employed, frequently experience spray collapse under
flash boiling conditions. The collapsing spray impinging a wall involves a
complex multi-phase coupling mechanism. Once the spray impinges the wall, the
heat and mass transfer between the wall and the adhering liquid film complicates
the predictability of the fuel film characteristics. The quantitative evaluation
of fuel film is crucial for studies on wall impingement. Nonetheless, the
quantitative measurement of phase change fuel films necessitates addressing
multiple problems, including evaporation and vapor phase interference. This work
utilizes Mie scattering photography and Laser-Induced Exciplex Fluorescence
(LIEF) techniques to examine the multi-plume spray impingement process. The
impacts of the flash boiling superheat index and wall temperature were examined,
alongside a quantitative analysis of the evolutions in the thickness, area,
mass, and temperature of the adherent fuel film. The study results indicate that
the spray collapses at a low superheat index. High fuel temperature diminishes
liquid volume flux, hence reducing the mass of droplet impinging on the wall.
The mass of the deposited fuel film reduces with an increase in fuel
temperature, but low plate temperatures hinder evaporation and increase the mass
of fuel film. The interplay of impinging droplets and evaporation governs fuel
film’s thickness and temperature. Under flare flash boiling conditions, even
with a plate temperature of -25°C, the adhered film comprising merely 4% of the
total injected fuel.