Study of Hybrid Combustion usingParaffin Wax Fuel and N2O/N2O4 as Oxidizer BY Sandeep Patnala ME/SER/1022/09 UNDER THE GUIDANCE OF Dr. P.C. JOSHI DEPARTMENT OF SPACE ENGINEERING AND ROCKETRY BIRLA INSTITUTE OF TECHNOLOGY, MESRA
INTRODUCTION In Hybrid Propulsion Systems one component of the propellant is stored in liquid/gaseous phase while the other is stored in solid phase Depending on the physical states of fuel and oxidizer the hybrid system is divided in to Direct and Reverse hybrid propulsion system. Direct Hybrid Reverse Hybrid Oxidizer : Liquid Oxidizer : Solid Fuel : Solid Fuel : Liquid The specific impulse for hybrid rockets can range from 275 - 350 sec.
Advantages of HybridsCompared to SOLIDS LIQUIDSSimplicity -Chemically Simpler -Mechanically SimplerSafety -Reduced Chemical Explosion -Reduced fire hazards Hazards -Thrust Termination and abort possibilityPerformance Related -Better Isp performance -Higher Fuel Density -Throttling/Restart Capability -Easy inclusion of solid performance additivesOther -Reduced environmental -Reduced mass of the liquid impactCost -Reduced development costs are expected
Disadvantages of Hybrid Rockets:- Hybrid rockets also exhibit some disadvantages when compared to Liquid and Solid Rockets Oxidizer-to-Fuel ratio shift. Low regression rate. Uneven regression rate along the length of the grain. The primary hazards associated with hybrids are: Blow back. Hard starts.
Objective To study the following combustion characteristics of paraffin wax and nitrous oxide/nitrogen tetroxide hybrid system1. Regression rate at different injection pressures2. Mass consumption rate at different injection pressures3. Pressure-Time history of hybrid rocket motor4. Thrust and Specific impulse of above hybrid system
Methodology Literature review Design and fabrication of the rocket motor, mould with mandrel and nozzle Theoretical Analysis Preparation of N2O4 Experimental work Results
Literature ReviewM.A.Karabeyoglu, D.Altman ---> Ref (1)i)For several classes of liquefying fuels, the layer is hydro dynamically unstable leading to substantial droplet entrainment from the melt layer into the gas stream.ii) The susceptibility of a given fuel to this shear driven instability increases with decreasing viscosity and surface tension of the melt layer.iii)For practical oxidizer flux levels encountered in hybrid rocket applications, droplet entrainment can dominate direct gasification.iv)Several methods for increasing regression rates in hybrids were tested.
Liquid Layer Combustion TheoryA) Liquid Layer Thickness Estimation : The thickness of the energy liquid layer can be determined by the energy transfer relations in the solid and liquid phases. To estimate the liquid layer thickness following assumptions are made 1) Steady state regression rate of the slab 2) Physical properties of the material in both liquid and solid phase are uniform. 3) The effect of convection in the liquid layer is ignored. The possibility of the penetration of the thermal radiation into the fuel slab is analyzed and several assumptions are made in the radiation treatment, which are 1) Radiative flux is one dimensional. 2) Since the temperature levels in the slab are small, the contribution of radiation emitted by internal material to the radiative intensity is negligable. 3) The absorption coefficient of both liquid and solid material behaves like a gray body.
Under these simplifying assumptions, the thermal analysis yieldsthe melt layer thickness as -----> (1) The thickness parameter ψ mainly depends on : thermo physicalproperties and radiative characteristics of the fuel.The characteristic thermal thickness in the liquid phase is defined as -----> (2)Ψ can be found as a solution of the following nonlinear equation -----> (3) Here the following definitions of the effective heatingparameters are introduced for convenience. ----> (3a,3b,3c)
Ta, Tm, Tv =Initial, Melting and Vaporization temperatures of the fuel, respectively. Qr and Qw =Radiative and Total heat fluxes to the fuel surface. Cl and Cs =Average specific heats of the liquid and solid. Lm and Lv =latent heats for melting and vaporization. r and rv = Total and vaporization components of the regression rateAnother parameter that appears in the thickness expression isthe non-dimensional radiation parameter, Rl, which is defined asthe ratio of the thermal thickness to the radiative thickness inthe liquid phase. ------> (4)where, ‘a’ is the average gray body absorption coefficient in theliquid phase.
An explicit solution for the algebric nonlinear equation, eqn(3), for the general case could not be obtained.The two limiting cases are : 1) Rl >>1, the absorption of the radiation in the liquid layer is very large. The thickness can be solved explicitly as ----> (5) All the thermo physical properties of the fuel material are lumped in the logarithmic term and the Qr/Qc ratio does not affect the thickness. This case is important for propellants that are loaded with strongly absorbing material such as carbon black.2) Rl <<1, the absorption of the radiation in the liquid phase is small. The thickness of the thermal layer in the liquid is much smaller than the radiative thickness in the liquid and as a consequence all the radiative flux is absorbed in the solid. Unlike the other extreme, in this case the film thickness depends on the ratio of radiative heat flux to the convective heat flux and it can be expressed as • ----> (6)
B) Liquid Entrainment Relationships: The entrainment component of the regression rate depends on the parameters expressed below According to Gater and L’Ecuyer entrainment mass transfer rate, -------> (7) Where rent – entrainment portion of the regression rate Xe -- entrainment parameter mL -- liquid flow rate per unit area with in the melt layer In the light of the experimental findings and the results of the linear theory, a general empirical expression for the entrainment rate of liquid droplets in terms of the relevant properties of the hybrid motor is,
L.M.C.Santos , L.A.R.Almeida ---> ref (2)I. This paper deals with the combustion of ultra-high molecular weight polyethylene, and paraffin as the solid fuels burning with gaseous oxygen as well as N2O as the oxidizers.II. HTPB has been the preferred solid fuel for hybrid propulsion as the majority of experimental work shows.III. High density polyethylene in the pressure range of 20-40 bar resulted in regression rates no higher than 0.3mm/sec, while paraffin and oxygen with oxidizer mass flux ranging from 2 to 10g/cm2 s resulted in 1.0 mm/sec.
Tsong-Sheng Lee and Hsin-Luen Tsai ----> ref(3)I. A series of Paraffin-HTPB based nitrous oxide hybrid rocket fuels have been studies experimentally in a laboratory scale motor.II. About 3 to 4 times the regression rate is increased by burning paraffin wax as compared to regression rates of HTPB swirling O2 hybrid system as oxidizer mass flux at 90kg/ m2 sec.III. Isp of 50p fuel can reach up to 220sec wit oxidizer mass flux of 110kg/ m2 sec. Lower regression rate of HTPB fuel resulted in a lower Isp value and presenting fuel-lean combustion as oxidizer mass flux went beyond 80kg/ m2 sec due to part of the oxygen ejecting through nozzle directly without reacting with fuel vapors.
Alexandra Lazarav, Alon Gray ----> ref (4)I. The paper presents an experimental investigation of a laboratory hybrid motor employing paraffin fuel and gaseous oxidizer.II. Several types of paraffin has been tested and it is said that paraffin fuels have poor mechanical characteristics. This was over come by adding polymer to paraffin .III. Plain Paraffin :- Some fuel was blown through the nozzle, unburned, thus reducing the performance, while some fuel was accumulated in the motor.
Results of Static firing experiments with plain paraffin as fuelParaffin and Polymer mixture fuel : Several ideas were proposed to improve paraffin based fuel characteristics,performance and regression rate. Among those ideas adding nano sized aluminum particles andcarbon black to the plain paraffin improved mechanical properties. Thus improved densityspecific impulse and enhanced linear regression rate. Results of static firing experiments with paraffin wax and polymer mixture as fuel
Work Done Literature survey Design and modification of Combustion Chamber Design and fabrication of Mandrel, Case, Cover, Base Plate Design of Nozzle Evaluation of the performance parameters A small quantity of N2O4 has been Prepared
Work to be done Preparation of N2O4 Preparation of fuel Grain Experimental work Results and discussion
Procedure for the preparation of N2O4 Step 1 :-NaNO31. NaNO3 is placed in an open pan in an oven at approx 315°C for 20minutes or at a lesser temperature for a longer period.2. Care has to be taken to ensure that the temp remains below the decomposition temperature of NaNO3 ( 380°C).MnSO41. MnSO4 is roasted in an open pan in an oven for an hour at 315°C. Step 2 :-1. The powders are placed in a separate bag and are pound into pieces.2. 155gm of MnSO4 and 170gm of NaNO3 are mixed thoroughly and they are rolled to ensure proper mixing.
Step 3 :-1. The ingredients( reactants) are pound in a high temperature resistant vessel.2. The vessel is heated to produce vapors which are cooled using a condenser and an ice bath to get liquid N2O4.
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