Fuel film thickness measurements using refractive index matching in a stratified-charge SI engine operated on E30 and alkylate fuels

A numerical–experimental assessment of wall impingement models for spark-ignition direct-injection engines

“…Increases in film thickness beyond 15 µm could not be distinguished. These are significantly thicker films than those that have been resolved in in-cylinder measurements 1,46,47,49 that use the backscatter or reflection geometry (i.e. light source and camera on the same side of the roughened surface), for which the RIM technique underestimates film thickness as it approaches the RMS surface roughness.…”

“…Although many measurements using Mie scattering and laser-induced fluorescence have been made of free and impinging sprays, far fewer measurements have been made of the fuel films that form as a result of impinging sprays. In particular, quantitative, time-resolved, two-dimensional (2D) measurements of in-cylinder fuel film area, thickness, and volume began with the RIM measurements of Drake et al; 1,46 see Habchi et al, 42 Maligne and Bruneaux, 47 Henkel et al, 48 and Ding et al 49 for further applications and developments of the RIM technique. Laser-induced fluorescence techniques, which perform better for films thicker than those in this study (approximately >20 µm), were initially applied to study intake port fuel films in port fuel injection (PFI) engines 50 and more recently to SIDI engines.…”

“…light source and camera on the same side of the roughened surface), for which the RIM technique underestimates film thickness as it approaches the RMS surface roughness. 49…”

“…Apart from that effect, RIM measurements can also systematically underestimate film thickness. 49 In the backscatter or reflection geometry typically used for in-cylinder RIM measurements, 1,46,47,49 underestimation sets in as the film thickness approaches the RMS surface roughness. 49 As shown later (Figure 17), the largest simulated film thicknesses at 5 ms ASOI are about 15 µm.…”

“…49 In the backscatter or reflection geometry typically used for in-cylinder RIM measurements, 1,46,47,49 underestimation sets in as the film thickness approaches the RMS surface roughness. 49 As shown later (Figure 17), the largest simulated film thicknesses at 5 ms ASOI are about 15 µm. Recall that the RIM calibration (Figure 5(b)) shows declining sensitivity in the range of approximately 12–15 µm and no sensitivity to film thickness increases beyond ∼15 µm.…”