Regression Rate Characterization of HTPB‐Paraffin Based Solid Fuels for Hybrid Rocket

In this work, a new composition based on Paraffin wax and HTPB fuel, loaded with nanoparticles has been proposed for hybrid propulsion system. Lithium aluminium hydride (LiAlH4) and Magnesium hydride (MgH2) nanoparticles have been used as additives. A detailed rheological, thermal and ballistic characterisation has been carried out. The Magnesium hydride doped hybrid fuel exhibits lower viscosity as compared to the Lithium aluminium hydride doped one, leading to comparatively enhanced entrainment-aided combustion. LiAlH4 doped hybrid fuels also exhibit solid-like behaviour and thus greater stability in the solid phase in contrast to the MgH2 doped fuel. LiAlH4 doped fuel is thermally more stable and produces relatively greater residual-mass. The loading of nanoparticles significantly improves the fuel regression performance during ballistic firing. This can be attributed to the release of nascent hydrogen and metal nanoparticles during dehydrogenation of metal hydrides. Regression rate enhancement...

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Characterisation of paraffin-based hybrid rocket fuels loaded with nano-additives

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.

https://www.mdpi.com/2226-4310/6/3/28/pdf

Hybrid Rocket Underwater Propulsion: A Preliminary Assessment

A series of paraffin-based hybrid rocket fuel has been studied experimentally in a laboratory-scale motor. To enhance the regression rate of paraffin solid fuel, three types of grain configurations: Cylindrical, star, and helical grain configurations of paraffin wax have been developed and tested with gaseous oxygen. The helical fuel grain presented best performance among all the test ports. About 40.2 per cent and 20.6 per cent regression rates are increased by burning paraffin fuel with helical and star grain configuration respectively, as compared to cylindrical grain configuration at Gox=0.0191 g/mm2s. The regression rates were significantly influenced by the oxygen injection pressure varied between 344.7 kPa and 620.5 kPa. Furthermore, the experimentally obtained exponents of oxidizer mass flux for all three grain configurations have been found to be significantly different from those of the classical hybrid system. Finally, thrust-time traces for all three grain configurations were also studied. The result shown no significant increase or decrease in the amplitude of the thrust oscillations.Defence Science Journal, 2012, 62(5), pp.277-283, DOI:http://dx.doi.org/10.14429/dsj.62.2346

http://publications.drdo.gov.in/ojs/index.php/dsj/article/download/2346/1339

Testing of Paraffin-based Hybrid Rocket Fuel using Gaseous Oxygen Oxidiser

The Combustion characteristic with respect to initial port diameter variation in hybrid rocket motor is investigated using single port cylindrical grain. Experimental studies are performed with GOX and GN2O as oxidizers, and HDPE as fuel. Four initial port diameters of 10 mm, 15 mm, 20 mm and 25 mm were tested to see the effect of initial diameter on the burning rate where the regression rate behaved differently depending on the type of oxidizer. With GOX as oxidizer, the regression rates for the four port diameters are laid closely to each other so that they can be represented by a single empirical correlation i.e., as if the effect of initial port diameter can be negligible on the burning rate. At the contrary with GN2O, the regression rates are hardly represented by a single empirical correlation, and a large scatter of O/F ratio is observed with different initial diameters implying that the effect of initial port diameter can be important on the burning rate. While the behavior of regression rate on the variation of initial port diameter appeared differently depending on the type of oxidizer, the burning rate of fuel at a given oxidizer mass flow rate is decreased with increasing initial port diameter due to the decrease of heat flux from the flame to the solid fuel surface for both the oxidizer. A simple relation between thrust at the nozzle throat and initial geometry characteristic which is composed of oxidizer mass flow rate, initial port diameter and fuel grain length is proposed for the design method of hybrid rocket motor.

Combustion Characteristics of Initial Port Diameter Variation of Solid Fuel in Hybrid Rocket Motor

The purpose of this experimental research is to investigate combustion characteristics of cylindrical multi-port grain of a hybrid rocket motor. The physical model of concern includes an oxidizer supply system, a multi-port fuel grain, and a combustor with preand post chamber. Gaseous oxygen and polymer (PE and PMMA) are applied as the oxidizer and the fuel, respectively. In geometric points of view, the effects of the port number and the distance between ports on a regression rate are taken into account. Internal combustion performance was analyzed using smalland large scale motors: one is motor diameter of 50 mm and the other is 96 mm, with oxidizer mass flux ranging from 10 kg/m-sec to 300 kg/msec for both cases. The port number positively shifts the O/F ratio to near its optimum value as well as the oxidizer mass flux to the typical range influenced by pressure effects so that the fuel regression rate becomes fast as the port number increases to a typical number up to 4 ports. Emphasis was placed on merging effects among fuel gain ports having 4 and 5 port to analyze how port geometrical configuration may influence the chamber pressure and thrust drop.

http://enu.kz/repository/2009/AIAA-2009-5112.pdf

Suhyang Park

Papers

Combustion Characteristics of the Cylindrical Multi-port Grain for Hybrid Rocket Motor