Acrylonitrilebutadiene-styrene thermoplastic, widely mass-produced for noncombustion applications including household plumbing and structural materials, is evaluated and compared with hydroxyl-terminated polybutadiene as a potential fuel for hybrid rocket motors. Acrylonitrilebutadiene-styrene has several mechanical properties, including its ability to be fabricated into a wide variety of shapes using fused deposition modeling, which are very attractive as a potential hybrid rocket fuel. The acrylonitrilebutadiene-styrene grains were fabricated using fused deposition modeling from existing rapid-prototyping stock materials composed of 50∶43∶7 butadiene, acrylonitrile, and styrene mole fractions. The acrylonitrilebutadiene-styrene grains were burned with nitrous oxide as the matching oxidizer and compared for performance and consistency against fuel grains of equal size cast from hydroxyl-terminated polybutadiene and burned with nitrous oxide. Test results demonstrate a higher burn-to-burn consistency for ...

Comparing Hydroxyl Terminated Polybutadiene and Acrylonitrile Butadiene Styrene as Hybrid Rocket Fuels

Results from a development campaign, where modern additive manufacturing methods are used to fabricate hybrid rocket fuel grains with embedded helical ports, are presented. The fuel grains were constructed from acrlyonitrile butadiene styrene using commercially available three-dimensional printer feedstock material. Gaseous oxygen is used as the oxidizer for this test campaign. When compared to cylindrical fuel ports, significant increases in fuel regression rates were observed, and these increases in regression rate diminished with time as the helical fuel port burns to become progressively more cylindrical. Comparisons to the helical pipe flow skin friction correlation developed by Mishra and Gupta indicate that increased skin friction only partially accounts for the increased regression rate. The Mishra–Gupta correlation underpredicts the regression rate amplification early in the fuel burn and overpredicts that value late in the burn. The authors conclude that radial wall-blowing due to fuel pyrolysis...

/pdf/high-regression-rate-hybrid-rocket-fuel-grains-with-helical-3y80u4jkg3.pdf

High Regression Rate Hybrid Rocket Fuel Grains with Helical Port Structures

Hydroxyl-terminated polybutadiene (HTPB) with high cis-1,4 content (>95.0%) has been prepared via a two-step method by taking commercial butadiene rubber (BR9000) as a starting material, including the one-pot synthesis of aldehyde-group-terminated polybutadiene (ATPB) in high efficiency and the subsequent reduction reaction. The double bonds distributed in linear polybutadiene were first epoxidized and then cleaved at the exact epoxidized sites. The epoxidation reaction by 3-chloroperbenzoic acid and chain-cleavage reaction by periodic acid are controllable, highly efficient, selective, and quantitative. Along with an epoxy percent increase, the molecular weight of ATPB prepared via a one-pot method decreased with a relatively narrow polydispersity index. The aldehyde groups in the chain ends were reduced by NaBH4 to produce HTPB, in which the high cis-1,4 content of BR was retained.

Preparation of Hydroxyl-Terminated Polybutadiene with High Cis-1,4 Content

This paper details the development of a new ignition system concept that circumvents many of the difficulties associated with the current state of the art for hybrid rocket ignition systems. The technology is based on the unique electrical breakdown properties of additively manufactured acrylonitrile butadiene styrene. Strategic application of an electric field across the top of an additively manufactured acrylonitrile butadiene styrene fuel grain induces an electrostatic arc along the horizontally stacked manufactured surface features, and results in a small amount of pyrolyzed fuel vapor. When this event occurs simultaneous with the introduction of an oxidizing flow, the ablated hydrocarbon vapor together with residual energy from the electrical arc rapidly seeds combustion. Multiple incremental prototype systems were designed, built, and tested. Best conditions for successful operation were discovered, including minimum ignition pressure, optimal geometry, and electrical power requirements. An embedded...

Development of a Power-Efficient, Restart-Capable Arc Ignitor for Hybrid Rockets

Facile synthesis of novel HTPBs and EHTPBs with high cis-1,4 content and extremely low glass transition temperature

Acrylonitrilebutadiene-styrene (ABS) thermoplastic is evaluated as a potential fuel for hybrid rocket motors and compared to the widely used fuel material Hydroxyl-Terminated Polybutadiene (HTPB). For this project Nitrous Oxide (N2O) is used as the matching oxidizer. ABS is widely mass-produced for non-combustion applications including household plumbing and structural materials. Analytical predictions for enthalpies of formation, products of combustion, and end-to-end motor performance are compared against staticburn test results for ABS fuel grain manufactured using Direct-Digital Manufacturing (DDM). The chemistry and performances of the ABS fuel grains are compared against fuel grains cast from HTPB. ABS grains were DDMfabricated from existing stock materials composed of 50:43:7 butadiene, acrylonitrile, and styrene mole fractions. The grains were tested and compared against HTPB grains of equal physical volume and dimension. Test results demonstrate a higher burn-to-burn consistency for ABS fuel grains, but slightly * Associate Professor, Mechanical and Aerospace Engineering Department, 4130 Old Main Hill, UMC 4130, Associate Fellow, AIAA. † Graduate Research Assistant, Mechanical and Aerospace Engineering Department, 4130 Old Main Hill, UMC 4130, Student Member, AIAA. ‡ Graduate Research Assistant, Mechanical and Aerospace Engineering Department, 4130 Old Main Hill, UMC 4130, Student Member, AIAA. 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 31 July 03 August 2011, San Diego, California AIAA 2011-5909

Analytical and Experimental Comparisons of HTPB and ABS as Hybrid Rocket Fuels

An enthalpy-balance fuel-grain regression model is presented. The regression model, based on the longitudinally averaged fuel recession rates, is shown to accurately predict the chamber pressure, thrust and specific impulse performance of small and medium scale hybrid rocket motors. The key to the model predictions is the longitudinal enthalpy balance between the fuel grain heat of ablation and the convective heat transfer from the flame zone to the model surface. Convective heat transfer is related to the surface skin friction using the Reynolds analogy for turbulent flow. Simple flat plate models are used to predict the longitudinally averaged skin friction coefficient. Chemical properties of the combustion products were evaluated using the NASA Computer Equilibrium with Applications (CEA) Combustion code. Model predictions for a nitrous oxide (N 2 O) and hydroxylterminated poly butadiene (HTPB) motor are compared to data from a small-scale test firing with a 10.2-cm diameter motor. Suggestions for model improvements are offered.

/pdf/correlation-of-hybrid-rocket-propellant-regression-20fllw1xnb.pdf

Correlation of Hybrid Rocket Propellant Regression Measurements with Enthalpy-Balance Model Predictions

Deep-throttle static test results from an N2O and hydroxyl-terminated polybutadiene hybrid rocket motor are presented. The nominal 800 N thrust level was turned down to less than 12 N while still maintaining stable and controlled combustion. This 67∶1 turndown was accomplished using a commercial off-the-shelf throttle valve and a solid rocket motor case adapted for hybrid rocket testing. During throttled motor tests, the pressure ratio across the injector grows from a nominal value of 2.0 to greater than 3.0. This feature contrasts with the observed behavior of liquid rockets, where the injector pressure ratio drops significantly during deep throttle. This characteristic likely supports the observed hybrid burn stability during deep throttle. Data comparisons with a physics-based, throttled, hybrid rocket burn model accurately match for combustor pressure, thrust, and propellant consumption. At throttle levels approaching 20% of nominal, the N2O exiting the throttle valve is entirely in a vapor state. The...

Deep Throttle of a Nitrous Oxide and Hydroxyl-Terminated Polybutadiene Hybrid Rocket Motor

A closed-loop throttle controller for a laboratory-scale N2O and hydroxyl-terminated polybutadiene hybrid rocket motor is presented. Closed-loop throttling was achieved using commercial off-the-shelf valve hardware and a commercially available motor case adapted for hybrid rocket testing. Multiple and open- and closed-loop tests were performed to demonstrate that closed-loop control can significantly reduce the run-to-run burn variability typical of hybrid rocket motors. Closed-loop proportional/integral control algorithms featuring thrust or pressure feedback were used to track prescribed step and linear ramp profiles. Because the relationship between the selected throttle control valve position and the effective valve flow area was highly nonlinear, the effect of valve position on motor thrust/chamber pressure was measured open loop and curve fit to allow direct command of either total thrust or chamber pressure. Control law gains were tuned a priori using a numerical model and then adjusted using the a...

Closed-Loop Precision Throttling of a Hybrid Rocket Motor

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