This work was supported by the National Natural Science Foundation of China (Grant Nos. 11802315, 11872368 and 11927803) and Equipment Pre-Research Foundation of National Defense Key Laboratory (Grant No. 6142701190402).

1. Experimental setup and procedures
<ol>
	<li>Preparation of fuel grain 
	NOTE: The fuel grain with novel structure consisted of two parts, which are shown in Figure 4. As the main part of the novel grain, the paraffin-based fuel accounts for more than 80% of the total mass. The ABS substrate is used as an additional fuel. The preparation of this fuel grain was realized by combining 3D printing and centrifugal casting.
	<ol>
		<li>Substrate preparation
		<ol>
			<li>Open 3D software for ABS substrate drawing. 
			NOTE: The ABS substrate, which intended to provide the helical framework and support for the paraffin-based fuel, is comprised of twelve integrated blades that rotate 360&#176; clockwise in the axial direction and the wall.</li>
			<li>Save the 3D structure of the ABS substrate as a STL file.</li>
			<li>Open the 3D slicing software and import the structure of ABS substrate.</li>
			<li>Click Start Slicing, and select Speed print mode from Main Template. 
			NOTE: For the Primary Extruder choose ABS 1.75 mm.</li>
			<li>Double-click Speed, change the infill density to 100% and select Raft with Skirt for the Platform Addition. 
			NOTE: In order to improve the print quality and prevent warping, it is necessary to use a structure of print base (Raft with Skirt) to increase the contact area between the print body and the bottom plate.</li>
			<li>Click Save and Close, and then click Slice.</li>
			<li>Turn on the 3D printer and import the ABS substrate slice file.</li>
			<li>Set the temperature of the heated bed and nozzle to 100 and 240 &#176;C, respectively.</li>
			<li>Click Start to print after stabilization.</li>
		</ol>
		</li>
		<li>Paraffin-based fuel preparation
		<ol>
			<li>Prepare raw materials of paraffin, polyethylene (PE) wax, stearic acid, ethylene-vinyl acetate (EVA), and carbon powder. Configure the paraffin-based fuel according to the ratio of these components as 0.58:0.2:0.1:0.1:0.02. 
			NOTE: The specific information of each raw material is shown in the material table. The distribution ratio of paraffin-based fuel is not fixed and can be adjusted appropriately according to the purpose of the experiment. The purpose of adding carbon powder is to block radiant heat transfer and prevent the fuel grain from softening and collapsing during combustion.</li>
			<li>Place the configured raw materials into the melt mixer, and fully melt and stir until completely mixed. 
			NOTE: The paraffin-based fuel is heated to 120 &#176;C to ensure complete melting while preventing deformation of the ABS blades.</li>
		</ol>
		</li>
		<li>Fuel grain manufacturing 
		NOTE: To better demonstrate the effect of improving the combustion performance, paraffin-based fuel grains with the same composition were set as the control.
		<ol>
			<li>Place the ABS substrate into the centrifuge, and secure it with an end cap.</li>
			<li>Plug in the power and turn on the water-cooling pump switch.</li>
			<li>Turn on the centrifuge relay and increase the speed to 1400 rpm.</li>
			<li>Open the valve on the melt mixer and start casting. 
			NOTE: The molten paraffin-based fuel flows into the initial section of mold through the pipe and the end cover with a central opening. Under the effect of gravity, the liquid fuel spreads along the axial direction of the mold. Combined with effective cooling, a multiple-casting method, which is to divide the original one-time filling process into multiple times, is required to reduce the thermal stress.</li>
			<li>Remove the fuel grain and trim the shape.</li>
		</ol>
		</li>
		<li>Fuel grain measurement and recording
		<ol>
			<li>Measure and record the weight, length, and inner diameter of the fuel grain.</li>
			<li>Photograph the complete fuel grain.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of hybrid rocket engine system 
	NOTE: As shown in Figure 5, the hybrid rocket engine system consisted of four parts: the supply system, the ignition system, the engine, and the measurement and control system. The engine part included five parts: the torch igniter, the head, the combustion chamber, the post-combustion chamber, and the nozzle. The total length of the hybrid rocket engine is about 300 mm, and the inner diameter of the combustion chamber is 70 mm.
	<ol>
		<li>Hybrid rocket engine assembly 
		NOTE: The exhaustive details of the laboratory-scale hybrid rocket and the composition of the experimental system can be found in the previous paper32.
		<ol>
			<li>Fix the combustion chamber section of hybrid rocket engine on the slide rail.</li>
			<li>Load the fuel grain and install the post-combustion chamber section.</li>
			<li>Install the head and nozzle.</li>
			<li>Install the torch igniter on the head of the hybrid rocket engine.</li>
			<li>Install the spark plug and connect the power supply.</li>
		</ol>
		</li>
		<li>Connect the nitrogen, oxidizer, ignition methane, and ignition oxygen gas supply lines between the test bench and the gas cylinder.</li>
		<li>Connect the industrial computer, the multi-function data acquisition card, the mass flow controller, and the control box of the test bench.</li>
		<li>Power on the test bench, the mass flow controller, and the igniter.</li>
	</ol>
	</li>
	<li>Check the test system and set the experimental conditions.
	<ol>
		<li>Open the FlowDDE software and click Communications settings from the Communication.</li>
		<li>Click the corresponding connection interface and click OK.</li>
		<li>Click Open communication to establish communication with the flow controller and open the measurement and control program (MCP).</li>
		<li>Set the I/O channel of the multi-function data acquisition card and click Run to establish communication with the entire system.</li>
		<li>Check MCP running status and set to manual control mode. 
		NOTE: The MCP includes two modes: manual control is used for debugging and automatic control is used during experiments. The MCP written by LabVIEW is shown in Figure 6.</li>
		<li>Check the working condition of the spark plug and perform a valve test.</li>
		<li>Test data recording function.</li>
		<li>Open the setting interface and set test time, including valve opening and closing time, ignition time, and data recording duration. 
		NOTE: It takes some time for the mass flow controller to regulate the oxidizer flow to the set value, so the ignition time was set to 2 s after the supply of oxidizer.</li>
		<li>Set safety requirements and clear personnel from the experimental area.</li>
		<li>Open the cylinder valve and adjust the output pressure of the regulating valve according to the different mass flow rate conditions. 
		NOTE: With the supply pressure of 6MPa, the range of mass flow rate of the oxidizer is between 7 g/s and 29 g/s.</li>
		<li>Open the setting interface and set the oxidizer mass flow rate.</li>
	</ol>
	</li>
	<li>Hybrid rocket engine ignition
	<ol>
		<li>Turn on the camera.</li>
		<li>Set the MCP to automatic control mode and wait for trigger.</li>
		<li>Click Start on the MCP to start the experiment.</li>
		<li>After about one minute, click Stop on the MCP and turn off the camera.</li>
		<li>Close the gas cylinder and open the valve in the pipeline to relieve the pressure.</li>
		<li>Power off the test bench and remove the fuel grain.</li>
		<li>Repeat Step 1.1.4.</li>
	</ol>
	</li>
</ol>
2. Analysis of combustion performance
<ol>
	<li>Analysis of pressure oscillation 
	NOTE: The saved combustion chamber pressure data is represented as Pc(t).
	<ol>
		<li>Open Pc(t) with the data processing software.</li>
		<li>Choose the time period during the combustion process of the hybrid rocket engine.</li>
		<li>Select Analysis &#62; Signal Processing &#62; FFT to analyze the pressure oscillation.</li>
		<li>Use the default settings and click OK.</li>
	</ol>
	</li>
	<li>Analysis of regression rate
	<ol>
		<li>Calculate the regression rate of the fuel grain according to the following function: 
		<img alt="Equation 1" src="/files/ftp_upload/61555/61555equ01v2.jpg" /> 
		where &#916;D represent the change of average inner diameters of the solid fuel grain after the firing test; <img alt="Equation 5" src="/files/ftp_upload/61555/61555equ05.jpg" /> represent the change of quality of the fuel grain; L is the length of the fuel grain; &#961; is the average density of the solid fuel; t is the working time. 
		NOTE: The average density &#961; of the novel grain was expressed as: 
		<img alt="Equation 2" src="/files/ftp_upload/61555/61555equ02v2.jpg" /> 
		where <img alt="Equation 6" src="/files/ftp_upload/61555/61555equ06.jpg" /> and <img alt="Equation 7" src="/files/ftp_upload/61555/61555equ07.jpg" /> represent the density of the nested paraffin-based fuel and ABS material, respectively; <img alt="Equation 8" src="/files/ftp_upload/61555/61555equ08.jpg" /> and <img alt="Equation 9" src="/files/ftp_upload/61555/61555equ09.jpg" /> represent the mass fraction of the nested paraffin-based fuel and ABS material, respectively.</li>
		<li>Fit the regression rate as a function of oxidizer flux. 
		NOTE: The fitting function was selected as Allometric1 <img alt="Equation 10" src="/files/ftp_upload/61555/61555equ10.jpg" />, and the iterative algorithm was selected as Levenberg&#8211;Marquardt optimization algorithm.</li>
	</ol>
	</li>
	<li>Analysis of combustion efficiency
	<ol>
		<li>Calculate average combustion chamber pressure Pc by the following function: 
		<img alt="Equation 3" src="/files/ftp_upload/61555/61555equ03v2.jpg" /> 
		where Pc(t) represents the combustion chamber pressure at different times; t1 and tn represent the initial and final times at which the combustion chamber pressure was greater than 50% of the average pressure, respectively; n represents the number of pressure data points between and t1 and tn.</li>
		<li>Calculate the combustion characteristic velocity C&#8432; according to the following function: 
		<img alt="Equation 4" src="/files/ftp_upload/61555/61555equ04v2.jpg" /> 
		where Pc is the average combustion chamber pressure; At is the throat area; &#7743; is the total mass flow rate.</li>
		<li>Calculate the theoretical characteristic velocity of paraffin fuel C&#8432;P by NASA CEA code33.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Boiron, A. J., Cantwell, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2013).</li><li>Mazzetti, A., Merotto, L., Pinarello, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paraffin-based+hybrid+rocket+engines+applications:+A+review+and+a+market+perspective.">Paraffin-based hybrid rocket engines applications: A review and a market perspective.</a> Acta Astronautica. 126, 286-297 (2016).</li><li>Karabeyoglu, A., Zilliac, G., Cantwell, B. J., DeZilwa, S., Castellucci, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scale-Up+Tests+of+High+Regression+Rate+Paraffin-Based+Hybrid+Rocket+Fuels.">Scale-Up Tests of High Regression Rate Paraffin-Based Hybrid Rocket Fuels.</a> Journal of Propulsion and Power. 20 (6), 1037-1045 (2004).</li><li>Jens, E. T., Narsai, P., Cantwell, B., Hubbard, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2014).</li><li>Kuo, K. K., Chiaverini, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Fundamentals of Hybrid Rocket Combustion and Propulsion. , (2007).</li><li>Boardman, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 33rd Joint Propulsion Conference and Exhibit. , (1997).</li><li>Connell, T. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+Solid+Fuel+Combustion+in+a+Hybrid+Rocket+Motor+Using+Amorphous+Ti-Al-B+Nanopowder+Additives.">Enhancement of Solid Fuel Combustion in a Hybrid Rocket Motor Using Amorphous Ti-Al-B Nanopowder Additives.</a> Journal of Propulsion and Power. 35 (3), 662-665 (2019).</li><li>Veale, K., Adali, S., Pitot, J., Brooks, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+the+performance+and+structural+considerations+of+paraffin+wax+hybrid+rocket+fuels+with+additives.">A review of the performance and structural considerations of paraffin wax hybrid rocket fuels with additives.</a> Acta Astronautica. 141, 196-208 (2017).</li><li>Karakas, H., Kara, O., Ozkol, I., Karabeyoglu, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> AIAA Propulsion and Energy 2019 Forum. , (2019).</li><li>Di Martino, G. D., Mungiguerra, S., Carmicino, C., Savino, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Computational+fluid-dynamic+modeling+of+the+internal+ballistics+of+paraffin-fueled+hybrid+rocket.">Computational fluid-dynamic modeling of the internal ballistics of paraffin-fueled hybrid rocket.</a> Aerospace Science and Technology. 89, 431-444 (2019).</li><li>Leccese, G., Cavallini, E., Pizzarelli, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> AIAA Propulsion and Energy 2019 Forum. , (2019).</li><li>Cardoso, K. P., Ferr&#227;o, L. F. A., Kawachi, E. Y., Gomes, J. S., Nagamachi, M. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ballistic+Performance+of+Paraffin-Based+Solid+Fuels+Enhanced+by+Catalytic+Polymer+Degradation.">Ballistic Performance of Paraffin-Based Solid Fuels Enhanced by Catalytic Polymer Degradation.</a> Journal of Propulsion and Power. 35 (1), 115-124 (2019).</li><li>Paccagnella, E., Barato, F., Pavarin, D., Karabeyo&#287;lu, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+Parameters+of+Swirling+Oxidizer+Injection+in+Hybrid+Rocket+Motors.">Scaling Parameters of Swirling Oxidizer Injection in Hybrid Rocket Motors.</a> Journal of Propulsion and Power. 33 (6), 1378-1394 (2017).</li><li>Kumar, R., Ramakrishna, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+protrusion+on+the+enhancement+of+regression+rate.">Effect of protrusion on the enhancement of regression rate.</a> Aerospace Science and Technology. 39, 169-178 (2014).</li><li>Kumar, R., Ramakrishna, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+Hybrid+Fuel+Regression+Rate+Using+a+Bluff+Body.">Enhancement of Hybrid Fuel Regression Rate Using a Bluff Body.</a> Journal of Propulsion and Power. 30 (4), 909-916 (2014).</li><li>Degges, M. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2013).</li><li>Connell, T., Young, G., Beckett, K., Gonzalez, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> AIAA Scitech 2019 Forum. , (2019).</li><li>Whitmore, S., Peterson, Z., Eilers, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &amp; Exhibit. , (2011).</li><li>Whitmore, S. A., Armstrong, I. W., Heiner, M. C., Martinez, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 2018 Joint Propulsion Conference. , (2018).</li><li>Whitmore, S. A., Peterson, Z. W., Eilers, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparing+Hydroxyl+Terminated+Polybutadiene+and+Acrylonitrile+Butadiene+Styrene+as+Hybrid+Rocket+Fuels.">Comparing Hydroxyl Terminated Polybutadiene and Acrylonitrile Butadiene Styrene as Hybrid Rocket Fuels.</a> Journal of Propulsion and Power. 29 (3), 582-592 (2013).</li><li>Whitmore, S. A., Sobbi, M., Walker, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2014).</li><li>Whitmore, S. A., Walker, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+Model+for+Hybrid+Fuel+Regression+Rate+Amplification+Using+Helical+Ports.">Engineering Model for Hybrid Fuel Regression Rate Amplification Using Helical Ports.</a> Journal of Propulsion and Power. 33 (2), 398-407 (2017).</li><li>Creech, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 53rd AIAA Aerospace Sciences Meeting. , (2015).</li><li>Lyne, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 2018 Joint Propulsion Conference. , (2018).</li><li>Elliott, T. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 52nd AIAA/SAE/ASEE Joint Propulsion Conference. , (2016).</li><li>Armold, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2013).</li><li>Armold, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. , (2014).</li><li>Fuller, J., Ehrlich, D., Lu, P., Jansen, R., Hoffman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &amp; Exhibit. , (2011).</li><li>Lee, C., Na, Y., Lee, J. W., Byun, Y. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+induced+swirl+flow+on+regression+rate+of+hybrid+rocket+fuel+by+helical+grain+configuration.">Effect of induced swirl flow on regression rate of hybrid rocket fuel by helical grain configuration.</a> Aerospace Science and Technology. 11 (1), 68-76 (2007).</li><li>Tian, H., Li, Y., Li, C., Sun, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regression+rate+characteristics+of+hybrid+rocket+motor+with+helical+grain.">Regression rate characteristics of hybrid rocket motor with helical grain.</a> Aerospace Science and Technology. 68, 90-103 (2017).</li><li>Hitt, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 2018 Joint Propulsion Conference. , (2018).</li><li>Wang, Z., Lin, X., Li, F., Yu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combustion+performance+of+a+novel+hybrid+rocket+fuel+grain+with+a+nested+helical+structure.">Combustion performance of a novel hybrid rocket fuel grain with a nested helical structure.</a> Aerospace Science and Technology. 97, (2020).</li><li>McBride, J. B., Gordon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Computer Program for Calculation of Complex Chemical Equilibrium Compositions and APPlications. , (1996).</li><li>De Zilwa, S., Zilliac, G., Karabeyoglu, A., Reinath, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit. , (2003).</li><li>Franco, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regression+Rate+Design+Tailoring+Through+Vortex+Injection+in+Hybrid+Rocket+Motors.">Regression Rate Design Tailoring Through Vortex Injection in Hybrid Rocket Motors.</a> Journal of Spacecraft and Rockets. 57 (2), 278-290 (2020).</li></ol>

The authors have nothing to disclose.

The technique presented in this paper is a novel approach using a fuel grain with a nested helical structure. There are no difficulties in setting up the necessary equipment and facilities. The helical structure can be easily produced by 3D printing, and nesting of paraffin-based fuels can be easily carried out by centrifugal casting. Fused deposition molding (FDM) 3D printers are not expensive and the cost of centrifuges is low.
When the inner surface of the shaped fuel grain was found to hav...

A technique to improve the combustion performance of a hybrid rocket engine is urgently required. To date, practical applications of hybrid rocket engines are still far less than those of solid and liquid rocket engines1,2. The low regression rate of traditional fuels limits the improvement of thrust performance for the hybrid rocket engine3,4. In addition, its combustion efficiency is slightly lower than that of other chemical energy rockets due to internal diffusion combustion5, as shown in Figure 1. Although various techniques have been studied and developed, such as the use of multi-ports6, enhancing additives7,8,9, liquefying fuel10,11,12, swirl injection13, protrusions14, and bluff body15, these approaches are associated with problems in volume utilization, combustion efficiency, mechanical performance, and redundancy quality. Thus far, structural improvement of the fuel grain, which does not have these shortcomings, has attracted more attention as an effective means of improving combustion performance16,17. The advent of three-dimensional (3D) printing has brough an effective way to increase the performance of hybrid rocket engines through the ability to rapid and inexpensively produce either complex conventional grain designs or nonconventional fuel grains18,19,20,21,22,23,24,25,26,27,28,29,30. However, during the combustion process, these improvements in combustion performance diminishes with the characteristic structure burning, resulting in a decrease in combustion performance23. We have demonstrated that a novel design is useful in improving performance of hybrid rocket engines31. The detail for this technique and representative results is presented in this paper.
The fuel grain consists of a helical substrate made by acrylonitrile-butadiene-styrene (ABS) and a nested paraffin-based fuel. Based on centrifugal and 3D printing, the advantages of the two fuels with different regression rates were combined. The special helical structure of the fuel grain after combustion is shown in Figure 2. When gas passes through the fuel grain, numerous recirculation zones are simultaneously created at grooves between blades, which is shown in Figure 3. This characteristic structure on the inner surface increases the turbulence kinetic energy and swirl number in the combustion chamber, which increase the exchanges of both matter and energy in the combustion chamber. Ultimately, the regression rate of the novel fuel grain is effectively improved. The effect of improving the regression rate has been well proven: in particular, the regression rate of the novel fuel grain was demonstrated to be 20% higher than that of the paraffin-based fuel at the mass flux of 4 g/s&#183;cm2,32.
One advantage of the fuel grain with a nested helical structure is that it is simple to manufacture. The molding process mainly requires a melt mixer, a centrifuge, and a 3D printer. The ABS substrate formed by 3D printing greatly reduces the manufacturing cost. Another significant and unique advantage is that the enhancement effect does not disappear during the combustion process.
This paper presents the experimental system and procedure for improving the combustion performance of a hybrid rocket engine using the novel fuel grain structure. Additionally, this paper presents three representative comparisons of combustion performance parameters to prove the feasibility of the technique, including oscillation frequency of combustion chamber pressure, regression rate, and combustion efficiency characterized by characteristic velocity.

<table>
	<tbody>
		<tr>
			<td>3D printer</td>
			<td>Raise3D</td>
			<td>N2 Plus</td>
			<td>305 &#215; 305 &#215; 605 mm</td>
		</tr>
		<tr>
			<td>3D drawing software</td>
			<td>Autodesk</td>
			<td>Inventor</td>
			<td></td>
		</tr>
		<tr>
			<td>ABS</td>
			<td>Raise3D</td>
			<td>ABS black</td>
			<td>1.75 mm</td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Sony</td>
			<td>A6000</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbon</td>
			<td>Aibeisi</td>
			<td>ATP-88AT</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifugal machine</td>
			<td>Luqiao Langbo Motor Co.Ltd</td>
			<td>Custom</td>
			<td>&#8804;1450 rpm</td>
		</tr>
		<tr>
			<td>Data processing software</td>
			<td>OriginLab</td>
			<td>Origin 2020</td>
			<td></td>
		</tr>
		<tr>
			<td>EVA</td>
			<td>DuPont Company</td>
			<td>360</td>
			<td>binder</td>
		</tr>
		<tr>
			<td>Mass flow controller</td>
			<td>Bronkhost</td>
			<td>F-203AV</td>
			<td>0-1500 ln/min</td>
		</tr>
		<tr>
			<td>Melt mixer</td>
			<td>Winzhou Chengyi Jixie Co.Ltd</td>
			<td>Custom</td>
			<td></td>
		</tr>
		<tr>
			<td>Multi-function data acquisition card</td>
			<td>NI</td>
			<td>USB-6211</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin</td>
			<td>Sinopec Group Company</td>
			<td>58#</td>
			<td>Fully refined paraffin, Melting point&#8776;58&#8451;</td>
		</tr>
		<tr>
			<td>PE wax</td>
			<td>Qatar petroleum chemical industry Company</td>
			<td>Custom</td>
			<td></td>
		</tr>
		<tr>
			<td>Slicing software</td>
			<td>Raise3D</td>
			<td>ideaMaker</td>
			<td></td>
		</tr>
		<tr>
			<td>Spark plug</td>
			<td>NGK</td>
			<td>PFR7S8EG</td>
			<td></td>
		</tr>
		<tr>
			<td>Stearic acid</td>
			<td>ical Reagent Company</td>
			<td>Custom</td>
			<td>hardener</td>
		</tr>
	</tbody>
</table>

improving the combustion performance of a hybrid rocket engine using a novel fuel grain with a nested helical structure

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the different regression rates of acrylonitrile butadiene styrene and paraffin-based fuels, which increase the exchanges of both matter and energy by swirl flow and recirculation zones formed at the grooves between the adjacent vanes. The centrifugal casting technique is used to cast the paraffin-based fuel into an acrylonitrile butadiene styrene substrate made by three-dimensional printing. Using oxygen as the oxidizer, a series of tests were conducted to investigate the combustion performance of the novel fuel grain. In comparison to paraffin-based fuel grains, the fuel grain with a nested helical structure, which can be maintained throughout the combustion process, showed significant improvement in the regression rate and great potential in improvement of combustion efficiency.

Figure 7 shows the changes in combustion chamber pressure and oxidizer mass flow rate. To provide the necessary time for flow regulation, the oxidizer enters the combustion chamber in advance. When the engine builds pressure in the combustion chamber, the oxygen mass flow rate drops rapidly and then maintains a relatively steady change. During the combustion process, the pressure in the combustion chamber remains relatively stable.
Images showing a comparison of c...

Watch this Scientific Journal Video about Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure at JoVE.com

Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

A technique utilizing a solid fuel grain with a novel nested helical structure to improve the combustion performance of a hybrid rocket engine is presented.

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the ...

improving-combustion-performance-hybrid-rocket-engine-using-novel

Microsoft Bing

Research

JoVE Journal

Engineering

5.6K Views.  Chinese Academy of Sciences. A technique utilizing a solid fuel grain with a novel nested helical structure to improve the combustion performance of a hybrid rocket engine is presented.

Video: Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.

A protocol for conducting thermopower wave experiments is presented. The synthesis of hybrid composites of a chemical fuel and micro/nanostructured material, manufacturing of a thermopower wave generator, and methods for measuring the corresponding physical phenomena are described.

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs ...

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Here, we present a protocol to perform sensitive, spatially resolved gas spectroscopy in the mid-infrared region, using degenerate four-wave mixing combined with upconversion detection.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species ...

A Polymer-based Piezoelectric Vibration Energy Harvester with a 3D Meshed-Core Structure

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy harvester to lower resonance frequency and increase output power. The fabrication process is mainly divided into two parts: three-dimensional photolithography for processing a 3D mesh structure, and a bonding process of piezoelectric films and the mesh structure. With the fabricated flexible mesh structure, we achieved the reduction of resonance frequency and improvement of output power, simultaneously. From the results of the vibration tests, the meshed-core-type vibration energy harvester (VEH) exhibited 42.6% higher output voltage than the solid-core-type VEH. In addition, the meshed-core-type VEH yielded 18.7 Hz of resonance frequency, 15.8% lower than the solid-core-type VEH, and 24.6 &#956;W of output power, 68.5% higher than the solid-core-type VEH. The advantage of the proposed method is that a complex and flexible structure with voids in three dimensions can be relatively easily fabricated in a short time by the inclined exposure method. As it is possible to lower the resonance frequency of the VEH by the mesh structure, use in low-frequency applications, such as wearable devices and house appliances, can be expected in the future.

In this study, we fabricated a flexible 3D mesh structure and applied it to the elastic layer of a bimorph cantilever-type vibration energy harvester for the purpose of lowering resonance frequency and increasing output power.

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy ...

A Rapid Method for Modeling a Variable Cycle Engine

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft engines. However, developing VCE requires high costs. Thus, it is essential to build a mathematical model when developing an aircraft engine, which may avoid a large number of real tests and reduce the cost dramatically. Modeling is also crucial in control law development. In this article, based on a graphical simulation environment, a rapid method for modeling a double bypass variable cycle engine using object-oriented modeling technology and modular hierarchical architecture is described. Firstly, the mathematical model of each component is built based on the thermodynamic calculation. Then, a hierarchical engine model is built via the combination of each component mathematical model and the N-R solver module. Finally, the static and dynamic simulations are carried out in the model and the simulation results prove the effectiveness of the modeling method. The VCE model built through this method has the advantages of clear structure and real-time observation.

Here, we present a protocol to build a component-level mathematical model for a variable cycle engine.

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft ...