Week 22/2019

From droplet to new engine design

Project manager Florian Meyer shows the experimental setup.
Project manager Florian Meyer shows the experimental setup.
Cryogenic at first, suddenly extremely hot – cryogenic liquid oxygen is used inside a rocket engine to burn with hydrogen and thus generate energy. What happens in detail in this highly complex combustion process has not yet been deciphered. Researchers at the Center of Applied Space Technology and Microgravity (ZARM) in Bremen want to change this – and in the process obtain information on how rocket engines can work more efficiently and be made smaller.

The process seems basically simple: liquid oxygen is injected into the combustion chamber of the rocket engine and burns there with the hydrogen present. The injected oxygen must be divided into as many tiny droplets as possible – in the end it is more like a spray – in order to obtain the largest possible surface area. This makes combustion faster and more efficient.

The exact way the chemical and physical processes interact is not yet known. The complexity is high: several million tiny droplets react with each other within a few seconds and at high speed. How do the individual droplets evaporate? Which pressures occur when and where? What are the interactions between the individual droplets? Even the most powerful computer today does not have the capacity to calculate this in this dimension.

Basic research for tomorrow's spaceflight

The HYDRA research project at ZARM investigates these processes using the simplest element: a single drop. In the 146-meter-high Bremen drop tower, the scientists generate a drop of oxygen and drop it down in a combustion chamber for five seconds. There it reacts with gaseous hydrogen, which is located in the combustion chamber. The reaction is ignited with a laser. Using special cameras and sensors, the scientists record exactly what is happening.

The 146-meter-high drop tower at ZARM – unique in Europe.

During the free fall in the tower, the experiment is in weightlessness, which among other things leads to the drop not having the usual elongated shape but being perfectly round. This makes calculations easier in this first step. In the course of the experiments, different concentrations of hydrogen as a fuel and different pressures will also be experimented with.

By observing the individual drops, the researchers hope to gain insights into the overall system. The next step could be to add a second drop to see how the two drops interact during combustion. The long-term vision: to one day understand and optimize the entire process.

Getting the most out of the rocket engine

The researchers want to gain insights into how the combustion process in rocket engines can be made more efficient. As a result, the combustion chambers, for example, could one day be made smaller. The consequence: the rocket as a whole can be made smaller, lighter and produced more cheaply. In view of new developments and increasing commercialization in space travel – keyword: New Space – that could be a decisive advantage and give European space travel an important edge.

ZARM is collaborating on the project with several partners, including the Leibniz Institute of Photonic Technology at the University of Jena and the University of Washington in the USA. The project is also financially supported by the German Aerospace Center (DLR). It runs until the end of 2019.