Experimental Investigation of High Frequency Combustion Instabilities in Liquid Rocket Engine
- Paper number
IAC-05-C4.3.08
- Author
Mr. Franck Richecoeur, CNRS, France
- Coauthor
Prof. Sébastien Candel, CNRS, France
- Coauthor
Dr. Sébastien Ducruix, CNRS, France
- Year
2005
- Abstract
The Delfi-C 3 nanosatellite successor, Delfi-n3Xt, is currently under development at Delft University of Technology. This three-unit CubeSat platform has been improved through the implementation of a high-speed downlink, three-axis stabilization and a single-point-of-failure free implementation of batteries in the electrical power system. Failure of the batteries will therefore not lead to failure of the primary mission as has, in the past, been the case with many other nanosatellite missions.
In this paper the functional analysis of the command and data handling system (CDHS) of Delfi-C 3 and the improved CDHS architecture of are presented with a comparison of functions and performance of both CHDSs. The main design drivers for the CDHS of Delfi-C 3 were the available technology and the absence of batteries. These design drivers enforced specific hardware components which, however, resulted in undesired behaviour during integration and testing. In particular low-speed devices on the bus were suppressing the performance of the CDHS and the high-speed systems of Delfi-C 3. Most issues were mitigated through software implementations.
Delfi-n3Xt requires a higher performance since much more data will be produced, stored and sent down with a high-speed downlink. The CDHS architecture of Delfi-n3Xt has been based on the Delfi-C 3 CDHS since it has to be operational in the event of battery failure. The CDHS architecture has been improved and extended so that it is capable of operating with low-speed devices in combination with high-speed processing and low-cost scientific data storage.
The first cryogenic rocket engines have been experimentally developed during the 50’s. At this time, experimental data on this phenomenon have been generated but hundreds of engines have been damaged by unexpected high frequency combustion instabilities coupled with the transverse acoustic mode of the combustion chamber. Geometric modifications of the combustion chamber allowed to reduce the amplitude of combustion oscillations and make the engine more stable but also less efficient. Nowadays, there is none theoretical tool available to predict the high frequency combustion instabilities (f above 1 kHz). Little progress has been made in this field because of a lack of fundamental information. It was therefore timely to take a new look at the problem and use state of the art experimental tools in well controlled model scale experiments. To this purpose, a model scale combustion chamber has been designed. Three injectors, similar to those used in engines and vertically aligned, are fed with real cryogenic propellants (LOx/GCH4), it operates at an elevated pressure, injection conditions are in the range characterizing real engines. One idea explored in the present work is that collective interactions constitute a fundamental source of combustion instability. The closely packed flame geometry of rocket engines produces interactions in the vicinity of the chamber back plane. Collisions between adjacent streams may enhance turbulence and augment the volumetric rate of reaction. These fundamental effects have not been extensively investigated in the past or at least no conclusions were given on the possible collective effects of such arrangements of closely packed highly reactive jets. The experimental set-up involves three main elements : a combustion chamber and a cryogenic feed system, three coaxial injectors forming interaction jet flames inside the chamber, an external source of modulation to excite one of the chamber transverse modes. The chamber has a rectangular section. Its upper and lower walls are respectively equipped with three and two pressure transducers while the lateral side walls comprise large transparent quartz windows allowing direct observation of the three flames in the visible and near UV range. The momentum flux ratio between the gas and liquid streams is then chosen in a range which is typical of real engines. Different injection parameters have been tested to obtain a flame sensitive to pressure fluctuations. These hot fire tests have shown that at low injection velocity (UCH4 = 90 m/s), the interactions between flames and acoustic were strong enough to be observed. The toothed wheel was linearly accelerated at 150 Hz/s 1 from 0 to 3500 Hz to determine eigenfrequencies of the chamber. The Fast Fourier Transform of the pressure signals allowed to determine three resonant frequencies : the first longitudinal mode (1450 Hz), a coupled mode (1680 Hz) and the first transverse mode (2345 Hz). The coupled and the first transverse mode are similar to those observed in real engines, and generate the strongest flame disturbance. In the second step, the system was modulated successively at 1680 Hz and 2345 Hz. With the modulation, the pressure fluctuations reached 10
- Abstract document
- Manuscript document
IAC-05-C4.3.08.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.