Quantitative comparison of fuel spray images obtained using ultrafast coherent and incoherent double-pulsed illumination

TL;DR

This paper compares fuel spray images captured with ultrafast coherent and incoherent illumination, demonstrating that incoherent supercontinuum illumination yields clearer images with reduced artifacts and better correlation with simulations.

Contribution

It introduces a quantitative comparison method for fuel spray imaging using ultrafast coherent and incoherent light sources, highlighting the advantages of supercontinuum-derived incoherent illumination.

Findings

Incoherent supercontinuum illumination produces clearer spray images.

Incoherent images show reduced speckle and diffraction artifacts.

Incoherent images correlate better with numerical simulations.

Abstract

We present a quantitative comparison between the high-pressure fuel spray images obtained experimentally using classical imaging with coherent and incoherent ultrafast illuminations recorded using a compatible CMOS camera. The ultrafast, incoherent illumination source was extracted from the supercontinuum generated by tightly focusing the femtosecond laser pulses in water. The average velocity maps computed using time-correlated image-pairs and spray edge complexity computed using the average curvature scale space maps are compared for the spray images obtained with the two illumination techniques and also for the numerically simulated spray using the coupled volume of fluid and level set method for interface tracking (direct numerical simulation or DNS). The spray images obtained with supercontinuum-derived, incoherent, ultrafast illumination are clearer, since the artifacts arising due to laser speckles and multiple diffraction effects are largely reduced and show a better correlation with the DNS results.