Glistening brightness. Temperature: some 1500 degrees Celsius. That’s the way a gas flame burns. This one here has an output of about 50 kilowatts. One could power a car with it, or heat a house. But this flame is burning for science. Researchers from the Technische Universität München ignite this fire. They are interested in how the gas burns.
A seemingly simple question. Yet, upon closer examination, it proves to be quite complicated. Because there is quite a bit of turbulence within the flame. At their test station the scientists are simulating the processes in the combustion chamber of a large gas turbine. Gas turbines, like the one here in the Irsching power plant. With an efficiency factor of over 60 percent, the gas and steam turbine in block 4 holds the world record. Modern gas turbines are miracles of technology. In the future they will need to become more efficient yet. More flexible and more environmentally friendly than they are today. But this is not so simple. The turbine blades rotate at the speed of a jet plane — only millimeters from the walls of the casing.
A very delicate system. In his laboratory at the Chair for Thermodynamics, the engineer Joachim Schwing is doing research on how the turbines need to be constructed, so that they can not only turn natural gas into electric power, but also artificially generated hydrogen or biogas. “Natural gas, hydrogen and biogas have very different compositions and therefore different reactivity, which leads to a wide spectrum of operational requirements that a gas turbine needs to fulfill in the future.” The centerpiece of the equipment is a combustion chamber made of heatproof quartz glass. That way the scientists can study the flame with different methods while making changes to the burner or the gas mixture. Combustion — there is an entire cascade of chemical reactions running here, all more or less dependent on pressure and temperature. Even minute concentration fluctuations in the mixture of fuel, gas and oxygen cause pressure and temperature changes. And these, in turn, have an impact on the flame. This can lead to self-oscillation, which could, in the worst case, destroy the turbine. With development costs of up to 500 million euros, it would be a catastrophe, if a new turbine had a tendency to self-oscillate when it is in operation. Based on this experimental data, the engineers develop predictive models on the computer to anticipate the behavior of the flame in the combustion chamber. The idea is to use these models to calculate how future turbines will behave under different conditions — even before they are built. The colleagues next door are also working towards this goal. In this laboratory the scientists investigate, how gas turbines might become even more environmentally friendly. The probe analyzes the nitrogen oxide content in the exhaust gas. Because a byproduct of combustion are toxic nitrogen oxides. Earlier experiments showed that a mixture with a lot of air and little fuel leads to low emissions of nitrogen oxides. Yet it is precisely these diluted mixtures that have a strong tendency to destructive self-oscillation. In the context of the “Power plant for the 21st century” project, the scientists examined how improved mixing of fuel and air can help stabilize combustion. In the meantime, the scientists have found a solution for high-frequency self-oscillation. It’s a small part, screwed to the combustion chamber. “Actually, it is a classical Helmholtz damper, which we are using here against high-frequency oscillations. It consists of a small inlet and a resonance chamber. This is a very old principle, actually, but it effectively reduces self-oscillation in the high-frequency range.” In the future, when wind power and solar energy feed more electricity into the net, new, more dynamic gas power plants will carry out an important control function. Yet, until the power plants of the future have achieved maximal efficiency and minimal environmental impact, with different fuels and under varying conditions, this flame will be ignited many more times.