1.Background Introduction

Understanding the combustion characteristics of aviation kerosene in depth and enhancing its performance are crucial for aircraft engines. However, the composition of aviation kerosene is extremely complex, making it difficult to establish an accurate fuel dynamics model that simulates the combustion reactions of all its components. In response to this challenge, researchers use surrogate fuels—fuel blends with known proportions and compositions—to mimic the combustion characteristics of real fuels and to develop mechanistic models. RP-3, which is widely used as aviation kerosene in China, has been the subject of simulation studies by many scholars.

2.Research Content

To investigate the combustion characteristics of RP-3, the Combustion Dynamics Research Team at Sichuan University employed surrogate components to explore its combustion properties and optimize parameters.

Image 1-- Schematic diagram of the experimental system

The research team mixed fuel with air and ignited it in the combustion chamber using an electronic spark. They employed a Revealer high-speed camera (X213) combined with a Schlieren imaging system to form a high-speed imaging system, which synchronously recorded the flame propagation morphology at a rate of 20,000fps. By controlling variables, they tested combustion characteristics under different pressures and temperatures. The high-speed imaging system could clearly record images of the fuel in the combustion chamber at every moment, and the combustion radius was calculated from these images to determine combustion speed and other parameters. The rendering is as below:

Image 2-- High-speed Schlieren images of flames in the combustion chamber under constant pressure (2 bar) and varying temperatures.

Image 3-- High-speed Schlieren images of flames in the combustion chamber at constant temperature (443K) and varying pressures.

3.Research Conclusion

1). A new RP-3 kerosene surrogate fuel has been developed, along with a detailed composition ratio. Combustion experiments compared the combustion characteristics, such as burning rates, of the surrogate fuel and RP-3 kerosene under different conditions.

2). The burning rate of the RP-3 surrogate fuel significantly increased with rising initial temperature or initial pressure. The burning rate peaked near the stoichiometric ratio at 1.1; additionally, experimental data and simulated burning rates were validated using the KSRM model.

3). The radius of the flame propagation in the initial stages was not consistent with the increase in pressure. This discrepancy might be related to the impact of excessive ignition energy and flame thickness on the unstable propagation of expanding flames.

4). With increasing pressure, the Markstein length of RP-3 kerosene decreased significantly. However, there was no significant difference in the Markstein length of RP-3 kerosene under different temperature conditions. Furthermore, it was found that the Markstein length of RP-3 kerosene was consistent with its substitute's performance, but the difference in Markstein length between RP-3 kerosene and its surrogate became pronounced on the fuel-rich side.

4. Summary of Industry Application

The observation system, composed of a high-speed camera paired with a Schlieren imaging device, is widely utilized to observe the boundary layers of airflows, combustion, shockwaves, thermal convection within gases, as well as flow fields in wind tunnels or water tunnels. This system assists researchers by making less tangible experimental phenomena more observable and recordable with clarity, providing researchers with a comprehensive solution. (This information originates from the Combustion Dynamics Research Team at Sichuan University.)