Investigation of Effect of Diaphragms on the Efficiency of Hybrid Rockets

Moon

Journal of Propulsion and Power

et al. 2015

A novel paraffin-based blends fuel prepared from pure paraffin wax of the alkane family with polyethylene of the alkene family is proposed and tested in a slab motor to visualize the droplet entrainment mechanism followed by a hybrid rocket motor test to analyze its combustion characteristics. The mechanical strength of the proposed blended fuel is investigated by increasing the polyethylene weight percent. The overall regression rate of 5 wt % of polyethylene with 95 wt % of pure paraffin is found to be 3.9 factors higher than that of a pure polyethylene. Improved combustion efficiency under the condition of a similar oxidizer mass flow rate range is achieved with respect to pure paraffin fuel in which performance gain is comparable to that of the SP-1a fuel of Stanford University. Spectrum analysis of the chamber pressure shows no critical instability mode for the range of this study. The blend fuel is found to be comparatively effective for the hybrid rocket fuel in terms of mechanical strength, combustion efficiency, combustion instability, and combustion performance. Nomenclature A f = cross-sectional area of final chamber, m 2 A i = cross-sectional area of initial chamber, m 2 A pf = cross-sectional area of final grain port, m 2 A pi = cross-sectional area of initial grain port, m 2 A t = exhaust nozzle throat area, m 2 a = regression rate coefficient c exp = experimental characteristic velocity, m∕s c theo = theoretical characteristic velocity, m∕s D pf = diameter of final grain port, m D pi = diameter of initial grain port, m G o = time-space-averaged oxidizer mass flux, kg∕m 2 -s H f = height of final slab fuel grain, m H i = height of initial slab fuel grain, m L f = fuel grain length, m _ m ent = entrained mass flux from fuel surface, kg∕m 2 -s _ m o = time-averaged oxidizer mass flow rate, g∕s n = oxidizer mass flux exponent P c = chamber pressure, MPa _ r = time-space-averaged fuel regression rate, mm∕s t b = burning time, s W f = fuel grain width, m α = dynamic pressure exponent β = thickness exponent γ = viscosity exponent η c = efficiency of characteristic velocity μ l = liquid layer viscosity, Pa-s π = surface tension exponent ρ f = fuel grain density, kg∕m 3 σ = surface tension, N∕m

mentioning

confidence: 99%

Evaluation of Paraffin–Polyethylene Blends as Novel Solid Fuel for Hybrid Rockets

Moon

Journal of Propulsion and Power

et al. 2015

51st AIAA/SAE/ASEE Joint Propulsion Conference

“…From thrust requirement (i.e., 30 kN), total and, of course, fuel and oxidizer mass flow rates are known, considering an optimal O/F ratio. For what concerns the regression of the fuel grain a firing time 30 s + 5s as margin has been considered and Grosse model [10,16] has been taken into account.…”

Section: A Solid Grain Dimensioningmentioning

confidence: 99%

Preliminary Design of a 30kN Paraffin-Based Hybrid Rocket Engine

Votta¹,

Clemente²

2015

One of the objectives of the HYPROB program is the development of tools, design and manufacturing methodologies applicable to hybrid systems and the verification of these technological developments through the realization and test of a 30 kN rocket engine. The technological demonstrator is based on nitrous oxide (N 2 O) as oxidizer and paraffin as propellant and will have most attractive capabilities of hybrid systems compared to solid or liquid engines, as throttability and re-ignition. The project targets to achieve a TRL of enabling technologies for hybrid propulsion equal to 5. The paper reports the study logic defined to achieve the goals of the project and the status of the technical activities related to the preliminary design of the demonstrator, based on a design tool developed ad-hoc. NomenclatureACE = Aerotherm Chemical Equilibrium CMA = Charring Material Ablation HRE = Hybrid Rocket Engine Isp = Specific Impulse M = Mach Number O/F = Oxidizer to fuel ratio P = Pressure r = Regration Rate RCS = Reaction Control System T = Temperature Subscripts C = Combustion chamber e = Exit

51st AIAA/SAE/ASEE Joint Propulsion Conference

“…Especially, low regression rate is one of the most significant shortcomings of conventional hybrid rockets. So far many techniques (such as swirling oxidizer injection, 7-9 insertion of diaphragms 10,11 in the combustion port, use of complex multi-port grain configurations, 12 etc.) have been attempted to improve the regression rates of hybrid rockets but all of these methods suffer from important drawbacks.…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis of Port Diameter Effect on Hybrid Rocket Fuel Regression Rate with Axial Injection

Bianchi¹,

Nasuti

Carmicino

2015

Numerical simulations of the flowfield in a hybrid rocket motor are carried out with a Reynolds averaged Navier-Stokes solver including detailed gas surface interaction modeling based on surface mass and energy balances. Results are compared with several test data obtained from two dedicated test campaigns conducted with static firings of a laboratoryscaled hybrid rocket in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene cylindrical grains through an axial conical subsonic nozzle. A first numerical rebuilding of all of the firing tests has been performed to validate the model, highlighting its prediction capabilities and modeling limits. Despite the several geometrical simplifications, which allowed relatively modest grid sizes to be used and efficient parametrical analysis to be performed, the presented CFD approach is fairly able to capture the main features of the motor internal ballistics both in terms of average chamber pressure and regression rate trends with oxidizer mass flux and port diameter. Computed flowfields showed the establishment of a significant recirculation region at the motor head end, which promotes propellant mixing, and raises the fuel regression rate. Numerical simulations, supported by the experimental results, demonstrated the main role played by the characteristics of this particular injection configuration in determining the fuel regression rate spatial distribution and trend, and clarified the mechanism for which the port diameter has a direct influence on the fuel regression. Nomenclaturē m = time-averaged mass flow rate, kg/ṡ ω i = species source term in control surface, kg/m 2 · ṡ m = mass blowing rate per unit area, kg/m 2 · ṡ q = heat flux, W/m 2 r = regression rate, m/ṡ w i = species source term in control volume, kg/m 3 · s η = inward (from solid to gas) coordinate normal to surface ρ = density, kg/m 3 D im = effective diffusion coefficient, m 2 /s h = enthalpy, J/kg k = thermal conductivity, W/m · K M = molecular weight of the species, kg/kmole N = number of species p = pressure, N/m 2 T = temperature, K v = velocity component normal to surface, m/s y = mass fraction y + = dimensionless wall distance Subscripts f = fuel i = species s = solid material w = wall Superscripts = average in time and spacê = average in space