Quickest heat flow sensor tested

When we start a car engine, combustion gases with very high temperatures of more than 1,000 degrees Celsius are produced. When these hit the cylinder and piston walls, very high thermal loads arise which are normally only rarely achieved, such as during the re-entry of a space shuttle into the earth’s atmosphere. Part of the thermal energy is dissipated via the combustion chamber walls, resulting in a dirty form of combustion and the formation of soot particles in the vicinity of the walls. Under the management of Prof. Dr. Tim Rödiger and in collaboration with the engine manufacturers Siegfried Spiess GmbH, a team of researchers at Landshut University of Applied Sciences has now developed a probe with which this heat flow can be determined directly through a temperature or pressure measurement. This allows the new technology to take the measurements ten to one hundred times more quickly than before. In the future, the method developed in the ALTPdev project could help improve combustion processes and the thermal models of engines, and thereby reduce the emissions of pollutants. The new technology is also relevant to the future research into alternative fuels and hydrogen-based propulsion systems. The Federal Ministry for Economic Affairs and Energy provided Landshut University of Applied Sciences with 220,000 euros in funding for the project, which was completed in July of this year.

Dynamometer test

Together with Research Assistants Konstantin Huber and Felix Gackstatter and the industrial partner Spiess, Rödiger carried out the set of measurements on a test bench with a specially-prepared engine block. “The part of the energy to be dissipated via the walls of the combustion chamber is what we call the heat loss flux,” explains Rödiger, drawing a comparison with human skin. In this context, our skin is like a heat flow sensor: “Sauna air at 90 degrees Celsius is something we can cope with well; contact with water that is 90 degrees would scald our skin, however.” This is due to the heat flow, which is significantly higher in water than in air.

Peak loads measurable for the first time

In a combustion engine, very high thermal loads can arise. “This is due to the rapid sequence of the ignition and combustion process,” explains Rödiger, “which means that very high heat fluxes can occur for a short time.” With the use of the new ALTP sensor (ALTP stands for atomic layer thermopile), it has now been possible to determine these in greater detail for the first time. “In this respect, the measurements show that the peak loads could be far higher than previous studies and models have predicted,” explains the Professor.

Relevant to alternative fuels and hydrogen

In the future, manufacturers of engines and other combustion systems, from the mobility sector to the energy sector, could benefit from the new method. “The new technology provides us with information which enables us to better understand the complex processes of combustion; it can be used, for instance, to develop better predictions on the formation of pollutants and the wear of components,” emphasizes Rödiger. The measurements could also help to improve engine and combustion management in the future, and to develop new engine concepts and more efficient models. “The information is particularly relevant to the study of alternative fuels,” highlights the Professor. In this context, hydrogen flames in engines and gas turbine combustors achieve even higher temperatures and burn much closer to the wall, resulting in even higher heat flux densities. This should be taken into account in the development of components in the future.

Measurement in the microsecond range

The new technology measures in the microsecond range and is therefore considered the quickest method worldwide. “Until now, the ALTP method has only been tested for short-term measurements in wind tunnels and test rigs,” explains Rödiger, “we have modified the technology so that it is easy to apply and can be used for high-stress cyclical, thermal and mechanical loads. The sensor is installed in the engine block with a direct connection to the combustion chamber, which means it has to be able to withstand the high temperatures and thermal loads as well as the immense pressure in the combustion chamber. Rödiger emphasizes: “Although we have used the sensor technology within the framework of our research project for our studies of the internal combustion engine, it also opens up a wide range of applications beyond this area.” About the project
The “ALTPdev - Development of a novel heat flow measurement methodology for high time resolution investigations of engine combustion processes” project ran from 2017 to 2021. Prof Tim Rödiger from Landshut University of Applied Sciences was responsible for the overall project management. The project partner is the company Siegfried Spiess Motorenbau GmbH. The Federal Ministry for Economic Affairs and Energy provided Landshut University of Applied Sciences with funding of 220,000 euros.