In [13, 14], a comprehensive study on the application of two-color laser-induced fluorescence in the temperature measurement of single-component droplets can be found. Mark Itel [12] extends this discussion to the case that the third detection frequency is used to treat two-component droplets. This technology requires a low concentration of temperature-sensitive fluorescent dye (rhodamine B in this case). The fluorescence of rhodamine B was induced by argon laser on the green line (K = 5 14.5 nm), and its intensity was also detected in three different spectral bands. An important feature of droplet temperature measurement is that the ratio of fluorescence intensity of these strips is independent of the size of the detected object. The local laser intensity and tracer concentration are only related to the temperature and composition of droplets. In addition, inferential measurement is also necessary, mainly to infer the temperature of droplets according to the intensity ratio.

This instruction is carried out at room temperature (such as turning off the hot air generator), and the liquid is sprayed before it breaks down into water droplets. When these conditions are met, it is safe to assume that the temperature corresponds to the temperature measured at the injector. This temperature is the same as the temperature measured by thermocouple and the ethanol volume fraction of the liquid in the syringe.

Two laser beams are focused into the LDA measuring container, and the volume is just the size of the fluorescence measuring probe. The fluorescence signal detected at the correct angle is connected to the optical fiber through the achromatic doublet lens. In order to detect only the fluorescence emission, the laser light (K = 5 14.5 nm) from the droplet will be eliminated by the notch filter. Then, the fluorescence signal is divided into three spectral bands by a spectroscope and an interference filter (Figure 2). Three devices with photomultiplier tubes are used for detection. The final signal processing process is completed by a multi-channel acquisition board with a sampling rate of 5 MHz. The error of temperature measurement is about 65438 0.3 degrees Celsius. But the characterization of ethanol volume fraction here is inaccurate, and the estimation error is about 4%. At this stage, it should be added that we have not measured the evolution of droplet size, but the initial diameter is determined by the fuel flow Q measured at the injector outlet.

Then, the droplet size d0 is destroyed: (Deduction formula of droplet size D0:)

(Formula omitted here)

Where f represent that frequency of the piezoelectric ceramics.

Where f represents the frequency of piezoelectric ceramics.