Experimental study on the evaporation characteristics of aviation kerosene with multidroplets

The fuel within the combustion chamber of an aircraft engine is fragmented and atomized into a group of droplets, including dense small droplets, through devices such as fuel injectors or fuel throwers. These droplets evaporate in the high-temperature convective environment of the combustion chamber and subsequently mix with high-pressure air for combustion. Previous studies have focused on single-droplet evaporation characteristics rather than actual droplet group characteristics, thereby neglecting the interaction between droplets. To address this issue, multidroplets evaporation experiments are conducted in this study. This article provides experimental data to support the numerical simulation theory of multidroplet evaporation and accordingly supplements and corrects the droplet evaporation model.

In the multidroplet evaporation experiments, the evaporation processes of single, double, and triple jet fuel droplets suspend by quartz fiber under static conditions at high temperatures of 400, 500, and 600 ℃ are captured using a high-speed camera. Thereafter, the images are processed at a specific frame rate. A self-programming software is used to isolate the main body of the droplet, and the images are imported into MATLAB data processing software to obtain the droplet evaporation characteristic curve. Linear fitting is performed on the stable section of the evaporation characteristic curve to determine the evaporation rate of the droplet. The range of droplet spacing select in the multidroplet evaporation experiments is 1—4 times the droplet diameter.

The results showed that at the same temperature, with increasing droplet spacing, the average evaporation rate of multiple droplets increased while the rate of change in evaporation rate decreased. The evaporation rate of multiple droplets tended to approach that of a single droplet and followed an approximate exponential trend. When the distance between droplets exceeded the critical distance, the mutual influence between droplets became weak enough to be ignored, and double droplets could be regarded as two independent single droplets. At this point, there was no difference between the evaporation rate of multiple and single droplets. However, when two droplets were sufficiently close, the mutual influence between them reached its maximum, and the average evaporation rate of the two droplets dropped to 80%—90% of that of a single droplet. As the temperature increased, the mutual influence between droplets became stronger, and accordingly, the critical droplet distance increased.

These experimental results are consistent with the theoretical model derivation. When the droplet spacing is less than the critical droplet spacing, the evaporation rate increases monotonously with increasing droplet spacing, and the rate of change gradually decreases to zero. When the distance between droplets exceed the critical distance, the evaporation rate of multiple droplets remain constant and is approximately equal to that of a single droplet. During the investigation of the empirical formula for multidroplet evaporation, the goodness of fit of the selected exponential form ranges between 0.899 and 0.983. This paper obtains experimental data on double droplets and triple droplets evaporation and obtains empirical formulas for droplet spacing and temperature of double droplets. The experimental data are consistent with theoretical analysis conclusions, providing experimental data support and theoretical innovation for multidroplets evaporation models.