High density hybrid rocket motor

Abstract

A high density, generally recognized as safe, hybrid rocket motor is described, having a density-specific impulse similar to a solid rocket motor, with good performance approaching or equal to a liquid rocket motor. These high density hybrid motors resolve the packaging efficiency/effectiveness problems limiting the application of safe, low cost hybrid motor technology.

Claims

1. A fuel that can be used for a rocket motor comprising: a. an oxidizer containing greater than 10 wt. % water and an ionic liquid, said ionic liquid having a density of greater than 1.3 g/cc; b. a fuel grain fabricated from a polymeric material with a density of at least 1.25 g/cc, said fuel grain contains about 10-50% metal fuel additions, said metal fuel additions including one or more metals selected from the group consisting of aluminum, aluminum-magnesium, magnesium, TiH.sub.2, AlMgB.sub.14, CaB.sub.6, AlB.sub.2, MgB.sub.2, SiB.sub.6, and boron.

2. The fuel as defined in claim 1, wherein said polymeric material has a density of at least about 1.35 g/cc.

3. The fuel as defined in claim 1, wherein said metal fuel additions are coated with a fluoropolymer, said coating of said fluoropolymer constituting 1-5% by weight of said metal fuel additions.

4. The fuel as defined in claim 1, said polymeric material includes one or more compounds selected from the group consisting of polyacetal, sorbitol, pentaerythritol triacrylate (PETA), polyoxymethylene (POM), polysaccharide, and high molecular weight carboxylic acid.

5. The fuel as defined in claim 1, wherein the fuel grain contains an accelerator or modifier at 0.05-5%.

6. The fuel as defined in claim 1, wherein said fuel grain includes an energetic compound that includes one or more compounds selected from glycidyl azide polymer (GAP), glycidyl nitramine polymer (polyGlyN), 3-nitratomethyl-3-methyloxetane polymer (polyNIMMO), pentaerythritol tetranitrate (PETN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), cyclotetramethylenetetramine (HMX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 1,1-diamino-2,2-dinitroethylene (FOX-7), furazan-based molecules such as diaminoazoxyfurazan, nitrocellulose, 3,3-Bis(azidomethyl)oxetane (BAMO), and other nitramines.

7. The fuel as defined in claim 1, wherein said ionic liquid includes one or more compounds selected from the group consisting of hydrolxylammonium nitrate (HAN), ammonium nitrate (AN), parachlorobenzotrifluoride, and aminopyridine (AP).

8. The fuel as defined in claim 1, further including a decomposition control agent, said decomposition control agent is a hydrocarbon soluble in said AN-HAN solution.

9. The fuel as defined in claim 8, wherein said decomposition control agent includes buffering agent, sequestering agent, or combinations thereof.

10. The fuel as defined in claim 1, wherein said oxidizer includes PVA.

11. A high density hybrid rocket motor which includes: a. an oxidizer solution having a density greater than 1.3 g/cc and containing at least 8% water; b. a fuel containing an oxygen-containing polymer having a density greater than 1.3 g/cc and containing one or more compounds selected from the group consisting of sorbitol, pentaerythritol triacrylate (PETA), polyoxymethylene (POM), polysaccharide, and carboxylic acid; c. a powdered metal fuel additive dispersed in the fuel that includes one or more components selected from the group consisting of aluminum, aluminum-magnesium alloy, titanium, boron, metal hydrides, silicon, and borides; and, wherein said oxidizer solution is atomized into fuel at pressures exceeding about 200 psig.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates two graphs directed to mass regression rates in a single port injector LGCP (long grain center perforate) hybrid test motor.

(2) FIG. 2 illustrates two graphs directed to theoretical performance CEA (Chemical Equilibrium with Applications) specific impulse calculations for POM, Sorbitol, and HTPB fuels.

(3) FIG. 3 is a graph directed to Delta-V performance versus O/F ratio for various high density oxidizer/fuel hybrid systems compared to state of the art upper stage bipropellant engine performance.

(4) FIG. 4 illustrates a HTHB-145 stage preliminary design for functional equivalent to PSRM-120 reference design.

(5) FIG. 5 illustrates a PID (piping and instrumentation diagram) and 4″ HRTM (High resolution Test Motor) as modified with close-coupled liquid oxidizer blowdown system.

(6) FIG. 6 illustrates a POM data plot showing stable combustion region with OXSOL and an image of firing.

DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS

(7) The present invention is related to a high density hybrid rocket motor having improved volumetric performance, and higher regression rates allows for efficient packaging and larger motors to be used. In particular, there is provided a high density hybrid rocket motor which has a density-specific impulse similar to a solid rocket motor, and with good performance.

(8) In one non-limiting configuration, the high density hybrid motor design uses inert gas pressurized OXSOL oxidizer, and electric ignition system, and a POM (Polyoxymethylene)/40% Al fuel grain. To meet PSRM-120 (Printed solid rocket motor) delta V requirements, nominal motor volumetric requirements are 18.6 liters (4.9 gallons) of OXSOL™.

(9) For a 16″ diameter tank size, the tank needs to have a 5.7″ length to accommodate the required volume. For packaging, a good design is a cylindrical tank with an internally domed head on the aft end, and an outward elliptical domed head on the top. The required volume can also be met by use of a 13″ diameter spherical tank. The walls of such tanks can be at least 0.20″ thick and optionally formed of magnesium or aluminum.

(10) Slightly more than ¼″ wall thickness may be required for a magnesium cylindrical case with elliptical ends for 1200 psig pressure rating (20% margin), equating to roughly 7 lbs. for the oxidizer tank, with 0.4″ elliptical ends. Total inert weight for the system is estimated at 32 lbs. when using magnesium tanks and cases, an aluminum gas bottle for the He pressurizing gas, steel valves and injectors, a 5.5″ carbon-phenolic nozzle and closure assembly, and graphite throat and post-combustion chamber. As can be appreciated, different materials and material thickness of one or more of the components may result in different weights.

(11) The fuel grains can require 763 in.sup.3 of volume. Such volume can translate into four 4″ grains 17.5″ long. These fuel grains are essentially the same volume and size of the 4″ HRTM motor (3.75″ grain diameter) tested with results shown in FIGS. 5 and 6. For a 500 psi rating, the wall thickness of a magnesium case is generally at least 0.045″, plus insulation.

(12) With 3/64″ phenolic insulation thickness (the grain acts as insulator as well), four 3.5″ motors can fit in a 10.5″ scribed circle. The spacing is actually dictated by the nozzle size—within a 16″ envelope, allowing for four 5.5″ nozzle diameters, matching the 6″ baseline design. Total mass of the four motor cases plus insulation is about 3.8 lbs fabricated from Mg alloy ( 1/16″ wall) extrusions with phenolic insulators. Mass estimates for the carbon-phenolic closures and nozzle assemblies is about 1.4 lbs/grain (5.6 lbs total). A 5000 psig He pressurization tank can be sized to run the 24″ open motor length, requiring a 5.5″ diameter to result in full system volume (oxidizer tank) end point pressure of 1100 psig. The center space with the 5.5″ nozzles can be nearly 7″ diameter, thus plenty of space for packaging. The wall thickness for a 6″ aluminum tank required for 5000 psig is about 0.4″, with a pressurization tank weight of 9 lbs. with elliptical ends, including He gas content. Adding about 7 lbs. for tubing, igniter, injector plates, battery, pressurization valve and structural supports, total inert mass for the hybrid motor is about 32 lbs., matching the initial estimates based on PSRM baseline designs (38 lbs. inert motor mass plus 50 lbs. payload).

(13) HDHB—145 Stage Design (High Density Hybrid, 145 Lbs Propellant).

(14) Motor configuration: pressurized cylindrical oxidizer tank, four 3.5″ diameter×15″ cylindrical grains with pressurization tank centered between grains.

(15) Motor total mass: 183 lbs.

(16) Total motor inert mass: 32 lbs.

(17) Motor diameter: 16″.

(18) Motor length: 38″.

(19) Total thrust: 36,685 lbf-sec.

(20) This design fits within the 17″×42″ volume constraint for the notional Nanolauncher design. Alternative designs, including a toroidal tank are not suitable for main thrust motor, but would be most desirable for a −30 orbital insertion motor, which would have one grain and roughly a 2 gallon tank. For a −30 design, oxidizer and pressurization tanks arranged around a central motor grain represent the (first analysis) optimal design.

(21) FIG. 6 illustrates the overall HDHB-145 stage design.

EXAMPLE 1

(22) A POM/Al hybrid rocket motor grain was prepared. Polyacetal motor grains were prepared by twin screw compounding followed by single screw extrusion into 3″ diameter rods that were cut to 12″ lengths. Polyacetal Twin screw extrusion compounding was completed on a W&P ZSK-30 with a processing profile consisting of 191° C. inlet temperature, 192-197° C. mixing zone temperature, 200° C. exit die, 103-105 rpm screw rate, and 50-60 torque. Single screw extrusion was completed at Apexco-ppsi to produce a solid fuel grain of 3″ diameter directly. Grains were then adhesively bonded into the phenolic insulator tubes. Extruded rods were cut to length and epoxy cured into 0.25″ thick phenolic paper tubes. ½″ diameter holes were bored into the bonded fuel grains using an extended twist drill mounted on a center stock on a lathe. The fuel grain was centered using a 4-jaw chuck and the ID was bored by drilling.

(23) The fuel grains were fired in a ground (non-flight weight motor with a 4″ configuration, noted as the high resolution test motor, at Penn State University. The 4″ HRTM motor was modified to allow for liquid oxidizer feed, and close-coupling of the liquid oxidizer in the system to minimize O.sub.2/OXSOL overlap. To ensure reliable ignition, ignition was carried out with gaseous oxygen which was switched to liquid OXSOL feed during the first half-second of the burn. The modifications included adding a storable non-volatile liquid oxidizer feed system with appropriate safety and purge features, and fabricating and installing a significantly lengthened motor pressure vessel on the Hybrid Rocket Test Motor (HRTM) to provide for an appropriate fuel grain length with pre- and post-combustion mixing regions. A Process and Instrumentation Diagram (P&ID) for the upgraded test setup is shown in FIG. 5. Gas manifolds and the control area were separated from the motor and stand by 12″ reinforced concrete test cell walls. All operations are remotely sequenced and monitored from the control area. All critical pressures were recorded. The control program monitored chamber and injector pressures for under- or over-pressure conditions and automatically aborted the test to a predetermined safe shutdown mode if any of the abort criteria were met. A manual abort button was also available on-screen, and the valves and connections revert to a failsafe condition (purges on, oxidizer flow off) if system power fails totally. To maximize system responsiveness and minimize oxidizer waste (and hazard), the OXSOL run tank was mounted on the motor stand, behind a blast plate. This run tank was only pressurized (with helium) seconds before the test starts, and was immediately depressurized and vented upon test completion or abort condition triggering. The data acquisition (DAQ) system was implemented on hardware independent of the LabVIEW-driven control system so that any potential failure or unexpected configuration in the control system could be monitored; commanded valve operations and igniter signals were recorded as digital signals in addition to analog pressure transducer readings at 1 KHZ.

(24) The motor illustrated in FIG. 5 was tested with a single 0.039″ port (⅛-flow) design was used, combined with the ½″ diameter initial fuel port. A series of motor firings were conducted over a range of pressures and oxidizer flow rations, using OXSOL™ as the oxidizer to validate motor performance and design calculations. At 350 psig, a full length, highly stable burn was achieved. FIG. 6 illustrates the pressure trace and valve operation for the 350 psig OXSOL-40% Al/POM burn. A full 8 second burn, with 5-6 seconds of stable OXSOL-POM combustion were achieved, and repeated at oxidizer/fuel rations ranging from 1-4. Efficiencies comparable to state of the art formulations in ground test were observed, validating the design calculations and motor performance estimates.

(25) It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. The invention has been described with reference to the preferred embodiments. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.