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A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 39906

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Special Issue Editor

Prof. Dr. Hui Tian

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Guest Editor

School of Astronautics, Beihang University, Beijing 100191, China
Interests: advanced rocket engine technology (hybrid, solid, liquid); computational fluid dynamics; combustion and flow simulation

Special Issue Information

Dear Colleagues,

In recent years, the successful applications of hybrid rocket engines have been gradually attracting the research interest of researchers around the world, such as space tourism and transportation, small launch vehicles, and sounding rockets. Due to their low cost, high safety, lower environmental impact, and high performance, hybrid rocket engines have the potential for rapid development and are favored by private and public entities. In addition, as interest in hybrid rocket propulsion grows among students and amateur rocket developers, hybrid rocket engines will have great prospects for use in next-generation rocket systems. A typical hybrid rocket engine adopts the liquid oxidizer and solid fuel as propellants, which are stored in a tank and combustion chamber, respectively. In hybrid rocket engines, the injected oxidizer and pyrolysis fuel are mixed and burned in the combustion chamber; the combustion model is typical non-premixed diffusion combustion and has unique advantages. In recent research, the key areas are mainly performance enhancement technology, combustion and flow simulation, optimization design, etc.

In this Special Issue, we invite contributions relating to the advancement of hybrid rocket engine technology, including, but not limited to: performance enhancement technology (such as paraffin-wax-based fuel, metallic additives, swirl oxidizer injection, unique grain design), combustion and flow simulation (such as large eddy simulation, dynamic numerical simulation, thermochemical erosion, heat transfer of radiation), molecular dynamics, overall optimization design, multidisciplinary design and optimization, optimization with uncertainty, feeding system design, engine component design, ablation-resistant nozzle technology, electric pump pressurized systems, thrust throttling technology, ignition technology, advanced measurement technology, and novel applications.

Prof. Dr. Hui Tian
Guest Editor

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Keywords

hybrid rocket engine
performance enhancement technology
combustion and flow theory
engine component design
thrust throttling, optimization, applications

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Published Papers (10 papers)

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Research

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18 pages, 9686 KiB

Open AccessArticle

Regression Rate and Combustion Efficiency of Composite Hybrid Rocket Grains Based on Modular Fuel Units

by Junjie Pan, Xin Lin, Zezhong Wang, Ruoyan Wang, Kun Wu, Jinhu Liang and Xilong Yu

Aerospace 2024, 11(4), 262; https://doi.org/10.3390/aerospace11040262 - 28 Mar 2024

Viewed by 1636

Abstract

This study investigated combustion characteristics of composite fuel grains designed based on a modular fuel unit strategy. The modular fuel unit comprised a periodical helical structure with nine acrylonitrile–butadiene–styrene helical blades. A paraffin-based fuel was embedded between adjacent blades. Two modifications of the helical structure framework were researched. One mirrored the helical blades, and the other periodically extended the helical blades by perforation. A laboratory-scale hybrid rocket engine was used to investigate combustion characteristics of the fuel grains at an oxygen mass flux of 2.1–6.0 g/(s·cm²). Compared with the composite fuel grain with periodically extended helical blades, the modified composite fuel grains exhibited higher regression rates and a faster rise of regression rates as the oxygen mass flux increased. At an oxygen mass flux of 6.0 g/(s·cm²), the regression rate of the composite fuel grains with perforation and mirrored helical blades increased by 8.0% and 14.1%, respectively. The oxygen-to-fuel distribution of the composite fuel grain with mirrored helical blades was more concentrated, and its combustion efficiency was stable. Flame structure characteristics in the combustion chamber were visualized using a radiation imaging technique. A rapid increase in flame thickness of the composite fuel grains based on the modular unit was observed, which was consistent with their high regression rates. A simplified numerical simulation was carried out to elucidate the mechanism of the modified modular units on performance enhancement of the composite hybrid rocket grains. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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16 pages, 14031 KiB

Open AccessArticle

Hybrid Rocket Engine Burnback Simulations Using Implicit Geometry Descriptions

by Jan Erik Zeriadtke, Joël Martin and Viola Wartemann

Aerospace 2024, 11(2), 103; https://doi.org/10.3390/aerospace11020103 - 23 Jan 2024

Cited by 1 | Viewed by 1684

Abstract

The performance of hybrid rocket engines is significantly influenced by the fuel geometry. Burnback simulations, to determine the fuel surface and fluid volume, are therefore an important tool for preliminary design. This work presents a method for the simulation of spatially constant burn-ups on arbitrary geometries. An implicit surface definition by means of a signed distance function is used to represent the fluid volume and the fuel block on tetrahedral meshes. Two methods each are used to determine the fluid volume and the burning surface. The first method is based on a direct integration of the signed distance function with the Heaviside function or the Dirac delta distribution, respectively. The second method linearly interpolates the position of an isosurface and thus reconstructs the fuel surface. Both methods are compared and validated with analytical results of four example geometries. Both calculations of the fluid volume and the calculation of the surface content with the interpolation method are characterized as first-order methods. With practicable mesh resolutions of one million computational cells, errors below two percent can be achieved. With the interpolation method, numerical meshes can also be exported for any time points of the burn. Finally, the application of the program to the fuel geometry of the Viserion hybrid rocket engine is demonstrated. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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12 pages, 12583 KiB

Open AccessArticle

Combustion Characteristics of HTPB-Based Hybrid Rocket Fuels: Using Nickel Oxide as the Polymer Matrix Pyrolysis Catalyst

by Hongsheng Yu, Xiaodong Yu, Hongwei Gao, Luigi T. DeLuca, Wei Zhang and Ruiqi Shen

Aerospace 2023, 10(9), 800; https://doi.org/10.3390/aerospace10090800 - 13 Sep 2023

Cited by 1 | Viewed by 1983

Abstract

The slow regression rate induced by the high pyrolysis difficulty has limited the application and development of hydroxyl-terminated polybutadiene (HTPB)-based fuels in hybrid rocket propulsion. Nickel oxide (NiO) shows the possibility of increasing the regression rate of HTPB-based fuels by catalyzing the pyrolysis process of the polymer matrix in our previous investigation; hence, this paper studies the NiO particles in the thermal decomposition and combustion of HTPB fuel grains. The DSC/TG test shows that NiO can intensely decrease the thermal stability of HTPB, and the catalytic effect of NiO is mainly reflected in the final decomposition stages of polybutadiene components. 5 wt% NiO enhances the regression rate by 19.4% and 13.7% under an oxygen mass flux of 50 kg/m²s and 150 kg/m²s, respectively. Further investigation shows that NiO particles will also cause the reduction of combustion heat and the agglomeration at the regressing surface while catalyzing the pyrolysis process, improving the thermal conductivity, and promoting the radiative heat transfer of the HTPB-based fuels; thus, more NiO additive (5 wt% < [NiO] ≤ 10 wt%) does not lead to a faster regression rate in HTPB-based fuels. This study demonstrates the catalytic effect of NiO on the polymer matrix for HTPB-based fuels, showing the attractive application prospects of this additive in HTPB-containing fuel grains. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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19 pages, 8125 KiB

Open AccessArticle

Combustion Characteristics of a Swirl-Radial-Injection Composite Fuel Grain with Applications in Hybrid Rockets

by Ruoyan Wang, Xin Lin, Zezhong Wang, Kun Wu, Zelin Zhang, Jiaxiao Luo, Fei Li and Xilong Yu

Aerospace 2023, 10(9), 759; https://doi.org/10.3390/aerospace10090759 - 28 Aug 2023

Cited by 2 | Viewed by 1861

Abstract

The combustion characteristics of a swirl-radial-injection composite fuel grain were experimentally and numerically investigated. This composite grain permits swirl-radial oxidizer injection based on three hollow helical blades, each having a constant hollow space allowing uniform oxidizer injection into the main chamber along the axial direction. The oxidizer enters from channel inlets located along a hollow outer wall. This wall, together with the three blades, is fabricated as one piece from acrylonitrile-butadiene-styrene using three-dimensional printing. Paraffin-based fuel is embedded in the spaces between adjacent blades. Firing tests were conducted with gaseous oxygen as the oxidizer, using oxidizer mass flow rates ranging from 7.45 to 30.68 g/s. Paraffin-based fuel grains using conventional fore-end injection were used for comparison. Regression rate boundaries were determined taking into account the erosion of the oxidizer channels. The data show that the regression rate was significantly increased even at the lower limit. Images of the combustion chamber flame and of the exhaust plume were also acquired. The flame was found to be concentrated in the main chamber and a smoky plume was observed, consistent with the high regression rate. A three-dimensional simulation was employed. The present design was found to improve fuel/oxidizer mixing and combustion efficiency compared with a fuel grain using fore-end injection. Both the experimental results and numerical simulations confirmed the potential of this swirl-radial-injection fuel grain. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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28 pages, 18145 KiB

Open AccessArticle

Experimental Investigation of a Swirling-Oxidizer-Flow-Type Hybrid Rocket Engine Using Low-Melting-Point Thermoplastic Fuel and Oxygen

by Tsuyoshi Oishi, Mitsuru Tamari and Takashi Sakurai

Aerospace 2023, 10(8), 713; https://doi.org/10.3390/aerospace10080713 - 15 Aug 2023

Viewed by 2298

Abstract

Hybrid rockets are safe and inexpensive; however, boundary-layer combustion poses a problem in achieving a fuel regression rate equivalent to that of solid propellants. The fundamental combustion conditions, such as the fuel regression rate of LT421, a paraffin-based low-melting-point thermoplastic fuel, were investigated using a swirling-flow combustion method. Firing tests were conducted using the oxygen mass flow rate and burn time parameters. The LT fuel exhibited an ignition delay compared to polypropylene, and the pressure increased slowly relative to the thrust. The combustion pressure increased or remained constant with time, suggesting that the fuel regression rate was more dependent on the oxygen mass flow rate than the oxidizer mass flux. The shear force generated in the grain owing to the swirling flow caused fuel-grain separation when the oxygen mass flow rate exceeded 100 g/s. Fuel-grain separation was prevented by modifying the case geometry. The maximum fuel regression rate obtained in the tests was 4.88 mm/s at an oxygen mass flow rate of 190 g/s and mass flux of 72.4 kg/(m²s), which was four times higher than that of polypropylene at the same oxidizer mass flux. The fuel regression rate correlation was obtained using the oxygen mass-flow-rate-based parameter, although further modification was necessary to apply this correlation when the burning time was varied. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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23 pages, 11575 KiB

Open AccessArticle

Experimental Research on Reconstruction Techniques for Instantaneous Regression Rate of Hybrid Rocket Motor with Single-Port Wagon Wheel Fuel Grain

by Tianfang Wei, Guobiao Cai, Hui Tian, Yuanjun Zhang, Chengen Li and Xiangyu Meng

Aerospace 2023, 10(5), 440; https://doi.org/10.3390/aerospace10050440 - 10 May 2023

Cited by 2 | Viewed by 1969

Abstract

This study investigated reconstruction techniques for building the instantaneous fuel regression rate of the hybrid rocket motor (HRM). Specifically, an experiment in a laboratory 500 N-class hybrid rocket motor with single-port wagon wheel fuel grain, operated with hydrogen peroxide (HP) and hydroxyl-terminated polybutadiene (HTPB) based fuel (including Al), was carried out. A piece of post-processing software was developed to reconstruct the instantaneous regression rate and other performance parameters of the HRM during the firing test. The results produced by the reconstruction techniques are in good agreement with experimental data obtained by traditional methods, with a maximum error of less than 5.75%. Moreover, compared with the traditional endpoint method, the reconstruction method had a significant advantage, which could ascertain the sensitivity of the regression rate to changes in the oxidizer mass flux and fit the formula of regression rate in a single firing test. Additionally, digital image processing techniques were employed to determine the axial distribution of the fuel regression rate after the test using computed tomography (CT) scanning. This served to verify the accuracy of the instantaneous reconstruction calculation. The error in the average regression rate between CT scanning and the reconstruction calculation was 1.91%, proving that the CT scanning and pixel statistic method of the calculating regression rate was practical for characterizing the axial distribution of the average regression rate during the firing test. In summary, the main objective of this study was to reconstruct the transient parameters of hybrid rocket motor with single-port wagon wheel fuel grain using reconstruction techniques, and to fit the formula of the regression rate through a single-firing test. Furthermore, this paper proposes a modified reconstruction method that is essential for investigating fuel regression rate during the firing test of HRMs. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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21 pages, 11701 KiB

Open AccessArticle

Experimental Investigation into Closed-Loop Control for HTPB-Based Hybrid Rocket Motors

by Guang Tan, Hui Tian, Zhongshuo Wang, Zihao Guo, Jingfei Gao, Yuanjun Zhang and Guobiao Cai

Aerospace 2023, 10(5), 421; https://doi.org/10.3390/aerospace10050421 - 29 Apr 2023

Cited by 3 | Viewed by 2108

Abstract

Space exploration greatly facilitates the development of advanced propulsion systems. Extensive research has shown that hybrid rocket motors have bright prospects for use in variable-thrust propulsion systems. However, the variable-thrust precision control of a hybrid rocket motor with a high-mass fraction of aluminum has not been adequately explored. In this paper, we propose a closed-loop control system for a high-performance laboratory-scale hybrid rocket motor, and verify its performance through tests on a hybrid rocket motor containing 98% hydrogen peroxide and hydroxyl-terminated polybutadiene with 58% of an aluminum additive. The results show that, first, the average value of thrust in the stable sections in the three stages were 400.7 N, 599.1 N, and 400.1 N when the target values were 400 N, 600 N, and 400 N, respectively. Second, the average thrust was stable, and the control error of the average value was better than 0.5%. Third, the real-time error in thrust was controlled to within ± 20 N with a steady-state error smaller than 5%. These results indicate that the proposed closed-loop control strategy for hybrid rocket motors with a high-mass fraction of aluminum can maintain a constant thrust and smooth transitions in case of variable thrust. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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Review

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27 pages, 1273 KiB

Open AccessReview

Bridging the Technology Gap: Strategies for Hybrid Rocket Engines

by Christopher Glaser, Jouke Hijlkema and Jérôme Anthoine

Aerospace 2023, 10(10), 901; https://doi.org/10.3390/aerospace10100901 - 22 Oct 2023

Cited by 9 | Viewed by 6703

Abstract

Hybrid rocket propulsion, first demonstrated by the Russian GIRD-09 rocket in 1933, combines liquid oxidizer and solid fuel for thrust generation. Despite numerous advantages, such as enhanced safety, controllability, and potential environmental benefits, hybrid propulsion has yet to achieve its full potential in space applications. In recent years, the research on hybrid propulsion has gained enormous momentum in both academia and industry. Recent accomplishments such as the altitude record for student rockets (64 km), the launch of the first electric pump-fed hybrid rocket, and a successful 25 s hovering test highlight the potential of hybrid rockets. However, although the hybrid community is growing constantly, industrial utilizations and in-space validations do not yet exist. In this work, we reassess the possibilities of hybrid rocket engines by presenting potential fields of applications from the literature. Most importantly, we identify the technical challenges that hinder the breakthrough of hybrid propulsion in the space sector and evaluate the technologies and approaches necessary to bridge the gaps in hybrid rocket development. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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22 pages, 2088 KiB

Open AccessReview

Review of Alternative Sustainable Fuels for Hybrid Rocket Propulsion

by Francesco Barato

Aerospace 2023, 10(7), 643; https://doi.org/10.3390/aerospace10070643 - 17 Jul 2023

Cited by 6 | Viewed by 11317

Abstract

Hybrid rockets using specific oxidizer–fuel combinations are considered a green alternative to current propulsion systems, as they do not release very toxic or polluting exhausts, but only much less harmful substances such as carbon monoxide/dioxide and soot. However, in a long-term vision where space access and rocket transportation become a daily routine all around the world, the simple use of current green propellants could begin to become insufficient if the rest of the industry already follows much stricter rules, which are expected to tighten significantly in the future, thereby making emissions from rocket flights no more negligible. In this paper, the possible use of alternative sustainable solid fuels for hybrid rockets that are not derived from fossil fuels and are ideally carbon neutral is investigated and discussed based on the available data in the hybrid literature and on the literature related to renewable fuels in general. Even if this topic is apparently far away from the current necessities, as hybrid propulsion is not yet operational, it is paramount to consider a long-term vision and associated research efforts to make sure that the potential hybrid propulsion introduction to the commercial market is more than a simple flash in the pan, but offers a solid opportunity. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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34 pages, 7816 KiB

Open AccessReview

Performance of Additively Manufactured Fuels for Hybrid Rockets

by Calvin Nguyen and James C. Thomas

Aerospace 2023, 10(6), 500; https://doi.org/10.3390/aerospace10060500 - 25 May 2023

Cited by 5 | Viewed by 4981

Abstract

Hybrid rocket engine (HRE) performance is dependent on fuel/oxidizer selection and fuel grain geometry. A literature review was performed to identify key trends and findings related to the application of the additive manufacturing (AM) of fuel systems for HREs. The effects of complex combustion port geometries, embedded structures, and end-burning systems, along with the use of metallic additives, turbulators, diaphragms, gel-like fuels, powdered fuels, liquid fuels, and liquifying fuels and their impact on regression rates, combustion efficiencies, and/or mechanical strength are thoroughly documented here. In general, the application of AM to HRE fuels can be implemented to increase regression rates and combustion efficiency, and tailor HRE designs. Chemical equilibrium analysis computations were completed to characterize the theoretical performance of HTPB and common AM fuels (ABS, PLA, PC, PMMA, Nylon 6, and a UV-based fuel) with common oxidizers (LOX and N₂O). AM fuels exhibit a similar theoretical performance as the commonly used HTPB fuel, and proper selection of the fuel can yield improved performance and design metrics. Development of AM approaches for HRE fuel design have significantly expanded their design trade space and should enable the competitive application of HREs for future propulsion missions. Full article

(This article belongs to the Special Issue Hybrid Rocket Engines)

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