Soot Volume Fraction Measurements from Droplet Combustion Experiments of Sooty Fuels
Caleb Riggins Mentor: Yuhao Xu Department of Mechanical Engineering Introduction: Kerosene (Jet A, Jet A1, JP-8, TR0) is a complex mixture widely used in aircraft engines. With the motivation to improve fuel efficiency, the aerospace industry strives to gain a better understanding of the combustion process of Kerosene and its components. For this purpose, free-floating droplet combustion experiments were conducted in the Combustion Integrated Rack (CIR) onboard the International Space Station (ISS) as part of NASA’s Flame Extinguishment Experiment (FLEX) and the subsequent FLEX-2 programs [1]. During the FLEX-2 experiments, a free-floating fuel droplet was ignited using energized Kanthal coils. The droplet burning history was recorded by a back-lit black and white (BW) camera, and the recorded images can be used to measure the droplet (D) and soot shell (Ds) diameters to obtain combustion properties such as the droplet burning rate (K) and soot stand-off ratio (SSR). In the past, various ways of extracting the droplet diameters from images were developed by researchers, and these methods can be summarized as either a rule-based computer algorithm or manual measurements performed by researchers [2]. However, none of these efforts focused on quantitatively extracting the soot volume fraction (SVF) from the experimental data, which reveals essential information on sooting dynamics and thus provides insights into potential solutions to reduce soot emissions during combustion. The objectives of this work include: (1) Access the experimental images of n-heptane combustion, as part of the FLEX program, in the NASA Physical Science Informatics (PSI) System (https://psi.nasa.gov/); (2) Develop an open-source program to extracting SVF from these experimental images; and (3) Examine the effects of the initial droplet diameter on the maximum SVF during the n-heptane droplet combustion processes. Materials and Methods: Soot volume fraction measurements provide essential information for studying soot growth, radiant transport, and post-flame particulates. Laser-induced incandescence (LII) and full-field light extinction method are favorably considered two nonintrusive approaches for SVF measurements. One major disadvantage of LII is that it does not provide absolute SVF as a relative measurement method, and thus it must be calibrated against other techniques [3]. Therefore, this study concerns the FFLEM technique to quantify soot emissions. FFLEM is based on the attenuation of light when a laser beam passes through the soot-containing region [4]. This project will develop a program to extract a light intensity profile and then perform the calculations to obtain SVF.
Results and Discussion: In this reporting period, the work has been focusing on performing relevant literature searches on the proposed topic to develop an understanding of the subject matter. The efforts also include obtaining relevant combustion images for obtaining SVF. Figure 1 shows typical images obtained for n-octane droplet combustion during ISS experiments.
Figure 1: Typical combustion BW image series from ISS combustion experiments [1]. 87
