# A Study on Combustion Characteristics of Insensitive Triple-Base Propellant
## 2 Materials and Methods  
The energetic materials used in the experiment were five kinds of triple-base propellants. The basic formulations of the five propellants were identical. The main component is a mixture of nitrocotton (NC), nitroglycerin (NG), nitroguanidine (NQ), and energetic plasticizer diazidonitrazapentane (DIANP). The mixture ratio of the formulations of five propellants was the same. Except for the blank propellant, the other four propellants were desensitized with a kind of desensitizer, but in different ways. In this paper, the five propellants were named 1\(\mu\), 2\(\mu\), 3\(\mu\), 4\(\mu\), and 5\(\mu\), according to their different desensitizing methods and desensitizer contents. The content of the desensitizer was 0%, 1%, 1.2%, 1.5%, and 1.2%, respectively. They were provided by Xi'an Modern Chemistry Institute. The appearance of the propellant was composed of white, solid large particles. The particle size was maintained at the millimeter level, with slight differences between different propellants. The structure was polyhedral in shape, with relatively smooth surface cutting and sharp corners, as well as some pits and bumps. Except for the blank propellant, the other four propellants were desensitized in the same desensitizer, but in different ways. The experimental system shown in Figure 1 contains four main parts: sample platform, laser diagnosis, chemiluminescence platform, and data acquisition platform. The sample platform was used to hold and ignite the propellant. The sample was placed on the tungsten sheet and made a round cake with a diameter of 10 mm and a thickness of 2 mm, and the sample mass was kept at 200 \(\pm\) 0.1 mg. Then, the tungsten sheet was placed on the object stage. The sample was ignited with the electronic pulse ignition method. Then, the propellant burned in self-propagation. The whole ignition and combustion processes were captured with a high-speed camera. The species of NO, OH, and NH were diagnosed with PLIF and chemiluminescence methods. The OH-PLIF laser platforms mainly involved the Nd:YAG laser, the dye laser, and the lens group. As an excellent laser diagnosis method, OH-PLIF was widely used in the combustion of gas, liquid, and solid fuels [20; 21; 22]. By generating a certain wavelength of laser light, the OH radical in the flame could be induced to produce fluorescence, and the two-dimensional concentration distribution of free radicals in the flame could be measured. NO/NH chemiluminescence did not require a laser platform, and an ICCD camera was employed to shoot. The OH-PLIF laser diagnostic platform used a 10 Hz Nd: YAG laser to output 566.046 nm pump laser after double frequency, and then it generated light with a wavelength of 283.023 nm and energy of 16 mJ after passing through the dye laser. Then, the light entered the lens group to generate a light sheet and passed through the sample center to excite the OH radicals during the reaction. Figure 1: Setup of the experimental system. Finally, the data acquisition platform mainly included a computer, a high-speed camera (Ametek, Wayne, NJ, USA, Phantom V611), and an ICCD camera (LaVision GmbH, Gottingen, Germany, LaVision Image Prox 2M). This platform was started and kept taking pictures to capture the whole combustion process. The experiment was carried out under normal temperature, pressure, and air environment. The detailed information of the experiments for diagnosing different species is as follows. (1) In the spontaneous light acquisition of combustion flame, a computer combining a high-speed camera were used to record the reaction and combustion process of the propellant. The resolution of the high-speed camera was 800 \(\times\) 600, the shooting rate was 600 fps, and the exposure time was 1600 s.  
(2) In the NO chemiluminescence experiment, the computer, combined with the ICCD camera, recorded the chemiluminescence signals of NO free radicals during the combustion of the propellant. A NO filter (FWHM:10 nm), with a central wavelength of 248 nm, was installed in front of the ICCD lens.