## 3 Results
### Microscopic and Macroscopic Droplet Measurements  
#### 3.2.1 LIF and Mie Signals of Toliso  
Figure 3 shows the simultaneous single-shot images of the LIF and the Mie signals of the Toliso droplet chain of the microscopic and macroscopic detection systems at reference conditions (293 K, 0.1 MPa). Due to the larger ROI, the macroscopic resolution was around 24 times lower than the microscopic resolution. The laser light enters the droplets from the left side. The images are shown zoomed for clarity. Bright spots and glare points become visible inside the droplets in the LIF and Mie images. Morphology-dependent resonance (MDR) effects are also visible, mainly in the form of a ring-shaped outer layer (see also Figure 7 below). The MDRs are commonly present at high laser fluence. The Mie images of the microscopic image (bottom row) mainly consist of two glare points. The intensity of the entrance glare point (reflection) is higher in comparison to the exiting glare point, as refraction and extinction effects take place within the droplet. The macroscopic image consists only of one very large and bright spot, which is also true for the macroscopic LIF image. In the microscopic LIF image, the signal exists throughout the whole droplet with a larger intensity in the center and bright spots at the surface. Figure 2: Fluorescence spectra for nile red (9.38 mg/L) in Toliso (**a**), E20 (**b**) at various temperatures normalized to 293 K, and a comparison of the two fuel mixtures plotted with the respective filter transmission curve (**c**). Fluorescence spectra were extracted from Reference [28]. The fitting curves for all evaluated individual LIF and Mie signals of Toliso are shown in Figure 4. as a function of the droplet diameter with the corresponding standard deviations of the curve fitting. In total, 31,019 single droplets were processed. The Mie curve shows a roughly quadratic dependency on the SMD and a relatively large standard deviation. In principle, the Mie scattering intensity was characterized by strong intensity oscillations with droplet size [14], which distinctly contribute to the large standard deviation. Nevertheless, the selected detection angle area smoothens these oscillations and enables a potential fitting procedure (further details can be found in previous work [15]). The microscopic LIF and the Mie signals at 293 K can be described by the following equations:  
\[I_{LIF\_Toliso\_293K_{(mix)}} = f\Big{(}d_{droplet}\Big{)} = 367.1\cdot d_{droplet}^{3,03} \tag{1}\] \[I_{Mie\_Toliso\_293K_{(mix)}} = f\Big{(}d_{droplet}\Big{)} = 53,777\cdot d_{droplet}^{1.87} \tag{2}\]  
Figure 4: Fitting curves for the experimental microscopic data for LIF and Mie signals as a function of the droplet diameter at the reference condition (293 K, nile red 100 mg/L) with their corresponding standard deviations (Toliso). Figure 3: Simultaneous microscopic and macroscopic LIF and Mie images of single micrometric Toliso droplets (50 \(\upmu\)m) at the reference conditions (293 K, nile red 100 mg/L). The LIF signal closely followed a \(d^{3}\) dependence and the Mie signal showed an approximate \(d^{2}\) dependence which is in accordance with the LIF/Mie theory [7; 8; 9; 10; 11; 12; 13; 14]. The comparison between the microscopic and macroscopic detection on the LIF/Mie ratio of Toliso with the corresponding standard deviations of the curve fitting is shown in Figure 5.  
The microscopic and macroscopic LIF/Mie ratios at 293 K can be described by the following equations:  
\[I_{\text{LIF}}/\text{Mie\_Toliso\_293K_{(micro)}}\ =\ f\big{(}d_{ droplet}\big{)}\ =\ 0.0092\cdot d_{ droplet}^{1.14} \tag{3}\]  
\[I_{\text{LIF}}/\text{Mie\_Toliso\_293K_{(micro)}}\ =\ f\big{(}d_{ droplet}\big{)}\ =\ 0.0123\cdot d_{ droplet}^{1.02} \tag{4}\]  
Both fitting curves showed the approximate \(d\) dependence according to the LIF/Mie ratio approach [6; 7]. The macroscopic fitting curve of Toliso lies below the microscopic function and showed a larger deviation from the microscopic fitting curve at increased droplet sizes.