Aseriesofstaticenginee ringswereconductedtoinvestigatethesolid-fuelregressionratebehaviorandoperating characteristicsofvortexhybridrocketengines.Thevortexhybridenginecone gurationischaracterizedbyacoaxial, coswirling, countere owing vortex combustion e eld in a cylindrical fuel port. To generate this e owe eld, oxidizer is injected through a swirl injector located between the aft end of the fuel grain and the inlet to the converging portion of the exit nozzle. Test e rings with thrusts up to 960 N were conducted with gaseous oxygen and hydroxylterminated polybutadiene solid fuel. Average fuel regression rates up to seven times larger than those in similar classical hybrids were measured. Empirical correlations were developed to describe accurately the experimental regression rates over more than an order of magnitude variation in mass e ux. In addition to local mass e ux and oxygeninjectionvelocity,geometricenginevariables,suchasenginecontractionratioand length-to-diameterratio, had a signie cant ine uence on the measured regression rates. Nondimensional regression rate and heat transfer correlations were also developed. Throttling and restart capability were demonstrated. Nomenclature A = cross-sectional area, cm 2 B = blowing parameter cp = isobaric specie c heat, J/kg ¢K D = port diameter, cm Ea = activation energy, kcal/mole G = local mass e ux, kg/m 2 ¢s Ginj = injection mass velocity, kg/m 2 ¢s GO = gaseous oxygen mass e ux, kg/m 2 ¢s

Solid-Fuel Regression Rate Behavior of Vortex Hybrid Rocket Engines

A series of static engine  rings, thermal pyrolysis experiments, and gas chromatograph/mass spectrometer tests were conducted to investigate the solid-fuel regression rate and heat-transfer behavior in a lab-scale hybrid rocket motor burning hydroxyl terminated polybutadiene/gaseous oxygen. A real-time, X-ray radiography system was used to determine the local, instantaneousregression rates. A dataanalysisprogramwas developedto help correlate the experimental data. The semi-empirical regression-rate correlation showed that, in addition to convection, radiation from soot and variable  uid properties across the boundary layer had signi cant effects on regressionrate behavior. The radiant heat  ux from sootwas relativelymore signi cant under lowmass  ux and low oxidizerto-fuel ratio conditions. Radiation from CO2 , H2O, and CO was quite small compared to convection and soot radiation. The nondimensional regression-rate correlation agreed with the experimental data to within § 3%. Stantonand Nusselt-number correlations were also developed and found to depend on both  ow regime and radiant heat  ux. The regression-rate correlations predicted independent data from both a lab-scale tube burner and the 11-in. (28 cm) JIRAD motor to very reasonable accuracy.

Regression-Rate and Heat-Transfer Correlations for Hybrid Rocket Combustion

Performance comparison of HTPB-based solid fuels containing nano-sized energetic powder in a cylindrical hybrid rocket motor

Nomenclature A = Arrhenius preexponential constant, mm/s B = blowing parameter, ρf r/(Gcf /2) Bmod = modified blowing parameter, B exp(q′′ r /q′′ c ) cs = fuel specific heat, J/kg · K cf = skin-friction coefficient cp = gas isobaric specific heat, J/kg · K C∗ = characteristic exhaust velocity, m/s D = diameter, cm D = mass diffusivity, m2/s Da = Damkohler number Dh = hydraulic diameter, cm Ea = activation energy, kcal/mole G = local, bulk mass flux, kg/m2 · s h = enthalpy, J/kg; port height, mm Isp = specific impulse, s k = absorption coefficient, kinetic rate constant K = concentration L = length of fuel slab, cm Le = Lewis number Np = particle number density Nu = Nusselt number O/F = oxidizer to fuel mass mixture ratio Pr = Prandtl number p = pressure, atm or MPa q′′ = heat flux, W/m2

Review of Solid-Fuel Regression Rate Behavior in Classical and Nonclassical Hybrid Rocket Motors

Material combustion in oxidant flows: Self-similar solutions

An experimental investigation of the thermal pyrolysis behavior of several hybrid-rocket solid fuels under rapid heating conditions was conducted to determine pyrolysis laws and to identify and quantify the products of fuel pyrolysis. The study focused on four fuel formulations: pure hydroxyl-terminated polybutadienes (HTPB), 80% HTPB/20% Alex, 80% HTPB/20% Al, and the Joint Industrial Research and Development fuel formulation. A rapid conductive-heating technique was developed and employed to determine Arrhenius-type pyrolysis laws. All four fuels displayed two sets of Arrhenius parameters, depending on the range of surface temperature. For pure HTPB,Ea = 4:91 kcal/mol andA = 11.04mm/s above722K, whileEa = 13:35 kcal/mol andA = 3965mm/s below 722 K. These results agree well with those obtained previously using a lab-scale hybridmotor operating under realistic conditions. The gas chromatograph/mass spectrometer tests of the nonmetalized fuels, using a  ash-heating oven, indicated that the relative concentrations of the pyrolyzed species depended strongly on temperature. For pure HTPB seven major products were identi ed, with 1,3-butadiene representing the dominantproduct at all temperatures tested, up to 1073 K. The measured mole fractions of the pyrolysis products and deduced pyrolysis laws of the fuels studied can be utilized in a comprehensive model simulation for combustion performance predictions.

Pyrolysis Behavior of Hybrid-Rocket Solid Fuels Under Rapid Heating Conditions

Pyrolysis behavior of hybrid rocket solid fuels under rapid heating conditions

Experiments were performed as a part of the Hybrid Propulsion Demonstration Program (HPDP) in order to demonstrate a N2O/HTPB hybrid sounding rocket. Multiple hybrid motors have been tested at Environmental Aeroscience Corporation in order to develop a high performance hybrid flight system. This paper will evaluate the performance of some static test motors, explain the combustion deficiencies associated with some designs, and discuss the evolution of the design toward the flight configuration.

Development of a n2o/htpb hybrid rocket motor

Numerous subscale experiments have been performed in order to examine the impact of certain features on the performance and stability of hybrid rocket motors. Proper evaluation of the recorded test data is necessary to accurately determine the performance of a given test. Under the best circumstances, only a single interpretation of the test data would be possible. A robust analytical technique is needed to ensure that the proper evaluation of performance has been obtained. Due to the nature of hybrid motors, the approaches that have been taken with solid and liquid rocket motors are not sufficient for the classification of hybrid rocket performance. New analytical techniques and a comprehensive analysis approach were developed to assess the large variability in performance that has been seen in the testing of hybrid motors. These techniques are based on industry standard thermochemistry codes and result in a complete assessment of performance for hybrid motors. If a rigorous, unbiased approach is applied, only one interpretation of the data will result. The purpose of this paper is to provide a working definition of the approach and processes that can be applied to the testing of hybrid rocket motors to properly evaluate performance without ambiguity or error.

A standardized technique for evaluating hybrid rocket motor performance

A series of four hybrid sounding rockets were successfully launched as part of the Hybrid Propulsion Demonstration Program (HPDP). These flights demonstrated a safe non-pyrophoric/nonpyrotechnic ignition system, inexpensive component manufacturing techniques, simple launch operations, and a quick launch turn-around time. This paper gives an overview of the design, flight, and recovery of the N2O/HTPB hybrid sounding rockets that were launched from NASA's Wallops Flight Facility.

H. Stephen Jones

Papers

Pyrolysis Behavior of Hybrid-Rocket Solid Fuels Under Rapid Heating Conditions

Pyrolysis behavior of hybrid rocket solid fuels under rapid heating conditions

Development of a n2o/htpb hybrid rocket motor

A standardized technique for evaluating hybrid rocket motor performance

Overview of hybrid sounding rocket program