Special Issue "Advances in Hybrid Rocket Technology and Related Analysis Methodologies"

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

Deadline for manuscript submissions: 31 May 2019

Special Issue Editor

Guest Editor
Dr. Carmine Carmicino

Department of Industrial Engineering, Aerospace Division, University of Naples Federico II, Piazzale Tecchio 80, Naples, Italy 80125
Website | E-Mail
Interests: fluid mechanics; modeling and simulation; computational fluid dynamics; hybrid rocket propulsion

Special Issue Information

Dear Colleagues,

Once perceived as a niche technology, for about a decade, hybrid rockets have enjoyed renewed interest from both the propulsion technical community and industry. Hybrid motors can be used in practically all applications where a rocket is employed, but there are certain cases where they present a superior fit, such as sounding rockets, tactical missile systems, launch boosters and the emerging field of commercial space transportation. The novel space tourism business, indeed, will benefit from their safety and lower recurrent development costs. The number of researchers dealing with this subject has increased more and more all over the globe along with the launch of student sounding rockets.

The key research areas include systems to improve the slow fuel regression rate, such as the selection of paraffin-wax-based fuel casting, the enhancement of wall heat transfer with nonstandard oxidizer injection methods and/or fuel grain configurations, the effects of the addition of energetic ingredients into the fuel, the suppression of combustion instability, and the optimization of engine components.

In this scenario, a broad spectrum of internal ballistics reconstruction techniques, CFD and numerical simulation strategies, as well as experimental methods have been developed to predict or assess motor performance with success. However, the real challenge facing researchers is probably inseminating the hybrid culture to enable the widespread adoption of this technology, which is still hindered, not for technical reasons, but due to societal factors like the stereotype represented by the mature solid and liquid propellant rockets.

This Special Issue addresses a broad area of topics, welcoming papers that will make a substantial contribution to the state of the art on: (i) motor performance and related issues, (ii) internal ballistics modeling, (iii) applied computational fluid dynamics, (iv) combustion stability, (v) analytical and computational acoustics, (vi) the design of novel hybrid rocket motor concepts, and (vii) experimental methods.

Dr. Carmine Carmicino
Guest Editor

Manuscript Submission Information

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Keywords

  • Fuel regression rate enhancement methods
  • Combustion instability
  • Motor internal ballistics
  • Numerical fluid-dynamic simulations
  • Oxidizer injection techniques
  • Nonstandard solid fuel grain configurations

Published Papers (5 papers)

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Research

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Open AccessArticle
Comprehensive Data Reduction for N2O/HDPE Hybrid Rocket Motor Performance Evaluation
Received: 31 January 2019 / Revised: 15 April 2019 / Accepted: 15 April 2019 / Published: 17 April 2019
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Abstract
Static firing tests of a hybrid rocket motor using liquid nitrous oxide (N2O) as the oxidizer and high-density polyethylene (HPDE) as the fuel are analyzed using a novel approach to data reduction that allows histories for fuel mass consumption, nozzle throat [...] Read more.
Static firing tests of a hybrid rocket motor using liquid nitrous oxide (N2O) as the oxidizer and high-density polyethylene (HPDE) as the fuel are analyzed using a novel approach to data reduction that allows histories for fuel mass consumption, nozzle throat erosion, characteristic exhaust velocity (c) efficiency, and nozzle throat wall temperature to be determined experimentally. This is done by firing a motor under the same conditions six times, varying only the burn time. Results show that fuel mass consumption was nearly perfectly repeatable, whereas the magnitude and timing of nozzle throat erosion was not. Correlations of the fuel regression rate result in oxidizer port mass flux exponents of 0.62 and 0.76. There is a transient time in the c efficiency histories of around 2.5 s, after which c efficiency remains relatively constant, even in the case of excessive nozzle throat erosion. Although nozzle erosion was not repeatable, the erosion onset factors were similar between tests, and greater than values in previous research in which oxygen was used as the oxidizer. Lastly, nozzle erosion rates exceed 0.15 mm/s for chamber pressures of 4 to 5 MPa. Full article
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Open AccessArticle
Viability of an Electrically Driven Pump-Fed Hybrid Rocket for Small Launcher Upper Stages
Received: 31 January 2019 / Revised: 4 March 2019 / Accepted: 11 March 2019 / Published: 14 March 2019
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Abstract
An electrically driven pump-fed cycle for a hybrid rocket engine is proposed and compared to a simpler gas-pressurized feed system. A liquid-oxygen/paraffin-based fuel hybrid rocket engine which powers the third stage of a Vega-like launcher is considered. Third-stage ignition conditions are assigned, and [...] Read more.
An electrically driven pump-fed cycle for a hybrid rocket engine is proposed and compared to a simpler gas-pressurized feed system. A liquid-oxygen/paraffin-based fuel hybrid rocket engine which powers the third stage of a Vega-like launcher is considered. Third-stage ignition conditions are assigned, and engine design and payload mass are defined by a proper set of parameters. Uncertainties in the classical regression rate correlation coefficients are taken into account and robust design optimization is carried out with an approach based on an epsilon-constrained evolutionary algorithm. A mission-specific objective function, which takes into account both the payload mass and the ability of the rocket to reach the required final orbit despite uncertainties, is determined by an indirect trajectory optimization approach. The target orbit is a 700 km altitude polar orbit. Results show that electrically driven pump-fed cycle is a viable option for the replacement of the conventional gas-pressurized feed system. Robustness in the design is granted and a remarkable payload gain is achieved, using both present and advanced technologies for electrical systems. Full article
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Open AccessArticle
Hybrid Rocket Underwater Propulsion: A Preliminary Assessment
Received: 28 January 2019 / Revised: 17 February 2019 / Accepted: 22 February 2019 / Published: 6 March 2019
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Abstract
This paper presents an attempt to use the hybrid rocket for marine applications with a 500 N class hybrid motor. A 5-port high density polyethylene (HDPE) fuel grain was used as a test-bed for the preliminary assessment of the underwater boosting device. A [...] Read more.
This paper presents an attempt to use the hybrid rocket for marine applications with a 500 N class hybrid motor. A 5-port high density polyethylene (HDPE) fuel grain was used as a test-bed for the preliminary assessment of the underwater boosting device. A rupture disc preset to burst at a given pressure was attached to the nozzle exit to prevent water intrusion where a careful hot-firing sequence was unconditionally required to avoid the wet environment within the chamber. The average thrust level around 450 N was delivered by both a ground test and an underwater test using a water-proof load cell. However, it was found that instantaneous underwater thrusts were prone to vibration, which was due in part to the wake structure downstream of the nozzle exit. Distinctive ignition curves depending on the rupture disc bursting pressure and oxidizer mass flow rate were also investigated. To assess the soft-start capability of the hybrid motor, the minimum power thrust, viewed as the idle test case, was evaluated by modulating the flow controlling valve. It was found that an optimum valve angle, delivering 16.3% of the full throttle test case, sustained the minimum thrust level. This preliminary study suggests that the throttable hybrid propulsion system can be a justifiable candidate for a short-duration, high-speed marine boosting system as an alternative to the solid underwater propulsion system. Full article
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Review

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Open AccessFeature PaperReview
The Application of Computational Thermo-Fluid-Dynamics to the Simulation of Hybrid Rocket Internal Ballistics with Classical or Liquefying Fuels: A Review
Received: 20 February 2019 / Revised: 7 May 2019 / Accepted: 11 May 2019 / Published: 16 May 2019
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Abstract
The computational fluid dynamics of hybrid rocket internal ballistics is becoming a key tool for reducing the engine operation uncertainties and development cost as well as for improving experimental data analysis. Nevertheless, its application still presents numerous challenges for the complexity of modeling [...] Read more.
The computational fluid dynamics of hybrid rocket internal ballistics is becoming a key tool for reducing the engine operation uncertainties and development cost as well as for improving experimental data analysis. Nevertheless, its application still presents numerous challenges for the complexity of modeling the phenomena involved in the fuel consumption mechanism and its coupling with the chemically reacting flowfield. This paper presents a review of the computational thermo-fluid-dynamic models developed for the internal ballistics of hybrid rockets burning gaseous oxygen with classical polymeric or paraffin-based fuels, with a special focus on the interaction between the fluid and the solid fuel surface. With the purpose of predicting the local fuel regression rate, which is the main parameter needed for the hybrid rocket design, the model is coupled with an improved gas/surface interface treatment based on local mass, energy and mean mixture-fraction balances, combined to either a pyrolysis-rate equation in the case of classical polymers, or to an additional equation for the liquid paraffin entrainment fraction of the total fuel consumption rate. A number of experimental test cases obtained from the static firing of two different laboratory-scale rockets are simulated to determine the models’ capabilities, showing very good agreement between the calculated and measured fuel regression rates with both standard pyrolyzing and liquefying fuels. The prediction of the chamber pressure measured with paraffin fuel resulted in it being more cumbersome for the single-phase flow assumption. The advantages and limitations of the models are discussed. Full article
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Open AccessReview
Innovative Methods to Enhance the Combustion Properties of Solid Fuels for Hybrid Rocket Propulsion
Received: 8 March 2019 / Revised: 17 April 2019 / Accepted: 17 April 2019 / Published: 22 April 2019
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Abstract
The low regression rates for hydroxyl-terminated polybutadiene (HTPB)-based solid fuels and poor mechanical properties for the alternative paraffin-based liquefying fuels make today hybrid rocket engines far from the outstanding accomplishments of solid motors and liquid engines. In this paper, a survey is conducted [...] Read more.
The low regression rates for hydroxyl-terminated polybutadiene (HTPB)-based solid fuels and poor mechanical properties for the alternative paraffin-based liquefying fuels make today hybrid rocket engines far from the outstanding accomplishments of solid motors and liquid engines. In this paper, a survey is conducted of several innovative methods under test to improve solid fuel properties, which include self-disintegration fuel structure (SDFS)/paraffin fuels, paraffin fuels with better mechanical properties, high thermal conductivity fuels and porous layer combustion fuels. In particular, concerning HTPB, new results about diverse insert and low-energy polymer particles enhancing the combustion properties of HTPB are presented. Compared to pure HTPB, regression rate can be increased up to 21% by adding particles of polymers such as 5% polyethylene or 10% oleamide. Concerning paraffin, new results about self-disintegrating composite fuels incorporating Magnesium particles (MgP) point out that 15% 1 μm- or 100 μm-MgP formulations increase regression rates by 163.2% or 82.1% respectively, at 335 kg/m2·s oxygen flux, compared to pure paraffin. Overall, composite solid fuels featuring self-disintegration structure appear the most promising innovative technique, since they allow separating the matrix regression from the combustion of the filler grains. Yet, the investigated methods are at their initial stage. Substantial work of refinement in this paper is for producing solid fuels to fulfill the needs of hybrid rocket propulsion. Full article
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