Short Description

For launchers different engine concepts exist (Fig. top, left). Depending on these engine concepts, requirements for engine flexible elements are different. The various engine concepts will be analyzed regarding their impact on lines/expansion joints requirements. The most severe requirements will be selected. In a first step elementary studies will be performed. These studies deal with material, coating, life time and vibration problems. Based on these studies, a draft design of a high temperature expansion joint will be elaborated.

The basic studies for engine flexible elements to be performed are:

  • Materials suitable for high and low temperature expansion joints Different types of materials, such as Fe- Co-, Ni-, Ti-based materials as well as others, will be investigated regarding their ability to use them as structural material and as material for bellows.
  • Lifetime of high temperature expansion joints Different methods exist to calculate the lifetime of bellows. The two most popular are the expansion joints manufacturers guideline EJMA Ed. 9 and DIN 14917. The two are analyzed and compared to finite element calculation of bellows as well as to test results known from other programs.
  • Surface coating of movable elements Surface coating shall reduce the friction of the movable elements. Especially for high temperature use the number of possible coatings is very limited. Wolfram disulfide, boron nitride, dicronite as well as Balinit Hardlube seem to be the most promising ones and show good high temperature resistance.
  • Necessity of “flow liners” for high flow velocities High flow velocities occur behind the preburners of gas generators or staged combustion engines. These high velocities can induce vibration into the movable elements (bellows) and considerably reduce their lifetime. Subject of this work is to analyze where the critical regions are and if methods exist to predict the vibration (eigenfrequency) with acceptable reliability (Fig. bottom).

Based on the elementary studies, a draft design of a light weight, high temperature expansion joint will be established. The design will be done for 100mm internal diameter expansion joint working at a temperature of 710K and facing a flow velocity of 280m/s. A very preliminary design of this expansion joint is given in Fig. top, right.

Project Partners


Magna Steyr Fahrzeugtechnik AG & Co KG, Division: Space Technology - Kurt Irnberger

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