ALCOHOL LOX STEAM GENERATOR TEST EXPERIENCE

Transcription

1 ALCOHOL LOX STEAM GENERATOR TEST EXPERIENCE Klaus Schäfer, Michael Dommers DLR, German Aerospace Center, Institute of Space Propulsion D Hardthausen / Lampoldshausen, Germany Klaus.Schaefer@dlr.de 1 ABSTRACT At the DLR test centre in Lampoldshausen there is a long experience in the development of rocket steam generators as a main subsystem for the altitude simulation. The rocket steam generators make it possible to supply the required quantities of steam at short notice with reduced investment and operating costs. The rocket steam generators are based on the combustion of liquid oxygen (LOX) and ethyl alcohol (ALC). The paper deals with the experience of the development of the steam generators and the operation at the altitude simulation P1.0 for satellite propulsion and P4.2 for altitude simulation of AESTUS upper stage engine. Igniter ALC Face Plate Combustion Chamber LOX 2 INTRODUCTION Altitude simulation of rocket engines and propulsion systems requires for a short large quantities of steam to operate the steam jet ejectors. The principle of rocket steam generators is to inject water into the hot gases of a rocket combustion chamber and to evaporate the water in a mixture chamber. The rocket steam generators make it possible to supply the required quantities of steam at short notice with reduced investment and operating costs. The concept of the new steam generators Fig. 1 is based on the combustion of Ethyl - alcohol and liquid oxygen operated by an electrical H2/O2 Igniter. The combustion chamber is water cooled. The sonic cross section is not at the combustion chamber, it s inside the steam nozzle several meters away. This influences the ignition and start up of the combustion chamber. Therefore the steam generator is developed in two steps, the combustion chamber mode like an rocket engine and the steam generator mode with mixture chamber, steam lines and steam nozzle. Fig. 1: Steam Generator Combustion Chamber 45 kg/s Combustion Chamber Mixture Chamber 1 Mixture Chamber 2 Steam lines Ejector Nozzle Fig. 2: Steam Generator 45 kg/s Proc. 2 nd Int. Conference on Green Propellants for Space Propulsion, Cagliari, Sardinia, Italy 7-8 June 2004 (ESA SP-557, October 2004)

2 3 DEVELOPMENT The principle function and experience of the main systems are: The development was done on the test position P1.1. Ignition System: The ignition system operates with gaseous hydrogen GH2 and gaseous oxygen GO2. A conventional spark plug is used for the electrical ignition. With the central GO2 jet and the GH2 injection coaxial in an outer ring the exhaust gas jet has a slightly H2-rich surface to reduce the head loads of the igniting tube. For the kg/s units the Igniter was moved from the central position on the face plate Fig. 1 to the side of the combustion chamber below the baffles Fig. 8. Hot gas tube GO2 Supply Fig. 3: 45 kg/s Steam Generator at Test Psition P1.1 Different units of steam generators are developed Tab. 1 for the altitude simulation P1.0, P4.1 and P4.2. Tab. 1: Steam Generator Development Spark GH2 supply year steam generator development 1995: 4,5 kg/s sub scale 1996: 28 kg/s sub scale 1997/1998: 10 kg/s P1.0 - satellites 1999/2000: 45 kg/s P4.2 - AESTUS 2001/2002: 16 kg/s P4.1 - VINCI 2000/2003: 55 kg/s P4.1 - VINCI Fig. 5: Igniter With the igniter we have a very good test experience. With the oxygen pre flow and the hydrogen rich Igniter flow the ignition of the steam generators are very reliable. Special points are the conditioning due to humidity particularly for the re ignition, and the gas mixing at the spark particularly the contents of oxygen. Combustor: There is a coaxial like on like injection. There are radial (4,5-16 kg/s unit) and checkerboard (45 55 kg/s unit) arrangements Fig. 6 of the like on like doublets. Fig. 4: Combustion Chamber Test 45 kg/s Fig. 6: Injection Element 45 kg/s

3 First Redesign: During development of the 45 kg/s unit the combustor becomes spontaneous combustion instability. The first redesign was the increasing of the injection holes on the fuel side d inj,fuel. The reasons were: Increasing water content of the fuel (from 10 % to 20 %Vol). Decrease the injection velocity of fuel. The latter point was dedicated from the empirical Hewitt criteria [1]. The experimental studies of the cavity ring were done by parameters studies of different length of the cavities, with and without N2 conditioning Fig. 9 of the cavities and by bomb tests. The results showed critical points for the control and set up of the acoustic conditions inside the cavity mainly during ignition and Start up. With the first redesign the steam generator becomes stable at operational points but become in-stable after triggering during Start up. Second Redesign: The second redesign was the adjustment of the Start up phase to avoid triggering and the implementation of acoustic absorber. The experimental studies of the acoustic absorber were: 1. Verification of the unstable mode and frequencies 2. Design of a quarter wave ring Fig. 7 and adaptation of the combustor. 3. Verification by testing (incl. bomb tests). 4. Designs of a three blade baffle Fig. 8 and adaptation of the combustor. 5. Verification by testing (incl. bomb tests). Adjustment crew Fig. 9: Test Results Cavities The baffles showed good behavior of damping during bomb tests Fig. 10 and sufficient water cooling. The nominal configuration today is with baffles. Bomb Cavity Cooling slots Fig. 10: Test Results Baffle Bomb Test Fig. 7: Quarter Wave Ring The first injection head was completely design out of copper. But with the experience during testing the head was modified Fig. 11 to an outer ring of stainless steel and cooper for the injection plate to increase the operational life. Fig. 8: Baffle Fig. 11: Ring and Face Plate

4 4 TEST FACILITY P1.0 The test facility was build for the altitude simulation of satellites engines up to 600 N thrust and to verify the behavior of new components and system for the altitude simulation. Since 2001 the test bench is in nominal operational conditions. deceleration inside the diffuser the exhaust gas is sucked by two steam jet ejector stages. The ejectors are supplied by one steam generator Fig. 14. The steam generator is supplied by pumps for Alc, LOX and water. With the P1.0 it s possible to test more than 2 h which less than 2 mbar vacuum simulation. Fig. 12: P1.0 test facility Fig. 14: 10 kg/s Steam Generator P1.0 Between 2001 and 2004 the steam generator was used for 53 tests and a total run off s (33,6 h) without modifications or exchange of hardware. Tab. 2: Tests with Steam Generator P1.0 (April 2004) Year Tests total failure Test total max Availabi lity N N [s] [s] [%] , , , , total , > 90 Fig. 13: P1.0 Principle 1: Vacuum chamber (V: 4,5 m³) 2: Steam Generator (Steam: 10 kg/s, 200 C, 20 bar, supplied by pumps) 3: First Steam Ejector (m Steam : 1,5 kg/s, P V : 60 mbar) 4: Second Steam Ejector (m Steam : 8 kg/s, P V : 280 mbar) 5: Auxiliary Nozzle (m Steam : 0,4 kg/s, P V : 1 mbar) 6: Diffuser ( = 0,35 m) 7: Exhaust Cooler (1400 kw, 1280 C 80 C) 8: Vacuum Flap 9: Emergency Flap 10: Engine The satellite engine is vertical mounted within a thrust measurement device inside a vacuum chamber. After The test failures were linked to the ignition and start up for the first 6.5 s. There was no test shut down with hot run of the engine due to steam generator. Lessons learned were concerning calcinations and sealing. Calcinations With increasing operational there was more and more calcinations inside the combustion chamber Fig. 15. Fig. 15: View 10 kg/s Combustion Chamber Exit

5 There were no big problems but the calcinations of the combustion chamber surface influences the water film cooling. To reduce the necessary maintenance and to prevent future problems the water is now treated to degree of hardness. The faceplate Fig. 16 was quit good after 53 tests. LOX underground water reservoir P4.2 ejectors ejector P4.1 condenser P4.1 LH2 steam generators Fig. 16: Face Plate 10 kg/s Combustion Chamber Sealing Another problem was the chosen sealing. Due to galvanic process for material with different electrical potential we have got problems with metallic seal during increasing operational. 5 TEST FACILITY P4.2 The test facility P4 consists of two test positions P4.2 for the altitude simulation AESTUS and P4.1 actual modified for the VINCI altitude simulation. Fig. 18: Principle P4 The steam generator plant consists of 5 systems. 4 systems with kg/s steam supplied by pumps and 1 system for 16 kg/s steam supplied by pressurisation of the run tanks Tab. 3. Tab. 3: Steam Generation P4 Steam generator plant P4: P4.2 P4.1 units: 2* 1 2+2* LOX kg/s 8,2 2,9 10 ALC kg/s 4,0 1,5 4,8 Water kg/s 32,8 11,6 40,2 Steam kg/s run s Steam kg/s )* switched between P4.1 and P4.2. With the 45 kg/s unit of P4.2 there was in 2003 and 2004 a total test of 8738 s in 19 tests performed. With the 16 kg/s unit there was in 2004 a total test of 555,3 s in 7 tests performed Tab. 4. Fig. 17: Test Facility P4 Both altitude simulations are supplied by the steam generator plant. The P4.2 requires 90 kg/s steam (corresponding to 250 MW thermal power) and P4.1 requires 235 kg/s steam (corresponding to 650 MW thermal power). Fig. 19: Steam Generator Plant P4

6 Tab. 4: Steam Generators P4 (April 2004) Year Tests Run total 45 kg/s unit 16 kg/s unit Run max Tests Run total Run max Before the first hot run the injection plate Fig. 22, the combustion chamber Fig. 23 and the mixture chamber is checked by water flow to verify the hydraulic and injection conditions. The calculated life cycles for the steam generators are higher than ,3 444 total , Tests were done in altitude configuration with two steam generators of 45 kg/s in parallel and 1663 s test. The steam generators 55 kg/s of P4.1 are still in commissioning phase. First test with 55 kg/s are successful performed including the re ignition. The problems are primarily linked to the MCC systems and mechanical problems Fig. 20. Fig. 22: Water Flow Check Injection Element % Other MCC digital Mechanical MCC analog Fig. 20: Non Conformances Steam Generator P4 Some tests start with a hard ignition. The triggering was damped and the combustion conditions were stable, thanks to the baffles. Up to now there were no problems concerning cooling behavior of the baffles. Fig. 23: Water Flow Check Combustion Chamber 6 CONCLUSION The new steam generators operate within the objectives of the development. Getting more and more experience the reliability is increasing. 7 REFERENCES Fig. 21: Water Flow Check Injection Plate and Baffle Each steam generator needs an individual setting for the hot run concerning supply conditions and sequences. 1. G. Krühsel, K. Schäfer, Design and Development of an Ethanol/LOX injection Head for Rocket Steam Generator (50 kg/s steam) and Experimental Study of Combustion Stability, Green Propellant Space Propulsion June, 2001, Noordwijk. 2. K. Schäfer, G. Krühsel, Advanced grteen propellant steam generator, Green Propellant Space Propulsion June, 2001, Noordwijk.