INVESTIGATION ON THE EFFECT OF INJECTOR FLOW NON UNIFORMITY ON THE PERFORMANCE OF A SMALL SCALE BIPROPELLANT LIQUID ENGINE
- Paper number
IAC-09.C4.P.10
- Author
Mr. P Arunkumar, Liquid Propulsion System centre, India
- Coauthor
Mr. B Ajith, Liquid Propulsion System centre, India
- Coauthor
Mr. C G Balan, Liquid Propulsion System centre, India
- Coauthor
Mr. S Venkateswaran, Liquid Propulsion System centre, India
- Year
2009
- Abstract
Liquid Propulsion Systems Centre (LPSC) is realizing small scale bipropellant engine / thruster for India’s Geostationary spacecraft as well as for interplanetary mission applications. These engines employ hypergolic earth storable propellant combination of Nitrogen Tetroxide(NTO) as oxidizer and Monomethyl Hydrazine (MMH) as fuel. The injector used is coaxial swirl type with oxidizer flowing through the outer flow passage and fuel through the inner flow passage. The process occurring in a liquid propellant thrust chamber can be classified into three general categories: atomization / vaporization, propellant mixing and chemical reaction. The propellant mixing process loss is usually around 2 percent which accounts for 6sec loss in specific impulse for a typical earth storable bipropellant thruster / engine. Only a few published literatures are available on the performance loss due to propellant mixing which is controlled by the non uniformity of the flow in the injector. This paper presents the results of the investigation carried out by experiment to evaluate the effect of non-uniformity of the flow on the performance, namely C* efficiency. The figure of merit of an injector is expressed by C* efficiency, (C*eff) which is defined as C*eff = Pc(x)At(x)100(x)g0/(mt(x)C*theor) Where Pc = Chamber pressure, At = Throat area, mt = Total propellant flow rate, C*theor= Theoretical C* which reflects the energy level of the propellant combination for an operating condition and g0= 9.81m/s2 C*eff is evaluated by doing hot tests at sea level condition. For a coaxial swirl injector operating at a defined conditions, C* efficiency depends on injector flow parameters such as pressure drop, flow cone angle and flow non uniformity. For a coaxial swirl injector, compared with inner flow passage, non uniformity of flow for outer passage is more sensitive to fabrication process, as it is near to the weld joint in the main injector body. Localized heating during welding affects the geometry of the critical nozzle exit dimension in the outer flow passage. Hence the evaluation was done for variations in non uniformity of the outer flow alone, keeping the inner flow uniformity untouched. \underline{{\bf Evaluation methodology }} Three numbers of injectors were evaluated by experiment. Initially the critical nozzle exit diameter was made undersize and after doing the welding in the main injector body, it was corrected to the designed value. Cold flow evaluation using de-mineralized water as simulant fluid was carried out for pressure drop, flow cone angle and non uniformity for both inner and outer flow passages. Flow non uniformity is evaluated from the mass flow distribution and is expressed as the standard deviation (SD) in simulant fluid collected at a specified distance from the injector face. Lower the SD, better the uniformity of flow. Hot test evaluation was carried out using a sea level version combustion chamber. After this, another run of weld was attempted at the joint near to the outer flow nozzle exit to deliberately affect the geometry of the critical exit dimension and cold and hot tests evaluations were repeated. Then a few micron cut was given on the exit dimension to improve the geometry in such a way that other flow parameters remain unaffected except the non uniformity of outer flow. Once again cold and hot test evaluations were carried out and the results are tabulated as given below. \underline{{\bf Test Results:}} All the tests were carried out for 300s each with a silicide coated sea level version chamber at a nominal fixed injection pressure and mixture ratio was maintained within 1.65+/- 0.05. No . Exit orifice condition . SD .. C*eff 1a . Good (Fresh)...............1.86 . 97.00 1b . Bad (After weld]..........5.80 . 96.50 1c . Good (After rework)....1.23 . 97.20 2a . Good (Fresh)...............2.50 . 97.10 2b . Bad (After weld]..........6.10 . 96.10 2c . Good (After rework)....1.42 . 97.30 3a . Good (Fresh)...............2.50 . 97.00 3b . Bad (After weld]..........4.70 . 96.50 3c . Good (After rework)....2.50 . 97.10 \underline{{\bf Concluding remarks}} Test results show a definite trend in all the three injectors with lower the non-uniformity or SD, the better the C* efficiency. It can be concluded that the variation in non uniformity (SD) of outer flow has a direct bearing on the C* efficiency as the propellant mixing process is affected. Also a value of SD upto 2.5 does not affect the performance significantly. For improving the efficiency of a bipropellant engine/ thruster employing coaxial swirl injector, flow non uniformity has a critical role to play.- Abstract document
- Manuscript document
IAC-09.C4.P.10.pdf (🔒 authorized access only).
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