Goal:
Design a catalytic combustion chamber concept for small aircraft engines based on hydrogen fuel.

Overview:
In order to reduce the pollutant emissions from the small aircraft engines, a catalytic combustor for hydrogen is investigated in the framework of the project. Furthermore, the functional demonstration within the characteristic operating range of small jet engines is proved from idle to take off. In the preliminary design of the catalytic combustion chamber, a simple analytical model is implemented in a new software program. This model is validated by means of an experimental parameter study of different catalysts. The final preliminary design is carried out with the help of the 3D numerical simulations and the analytical model to determine common parameters of the catalytic stabilized combustion concept. The instrumented combustion chamber is experimentally investigated at relevant inlet conditions of the jet engine at the hot flow test facility of the institute. Thereby, temperatures and pressures at different locations inside the combustion chamber are recorded and the exhaust emissions are analyzed. The design as well as the functional demonstration is carried out in a two–stage process. Initially a basic configuration is investigated, and based on that optimized configuration is designed.

Significance of the project:
Generally small aircraft engines are subjected to high specific fuel emissions due to the limitation of combustor size. It is known that in Europe, ACARE (Advisory Council for Aeronautical Research in Europe) has already called for reduction of nitrogen oxides (NOx) emissions by 80% by the year 2020 based on engine technologies. In favor of this issue, this project has an innovative concept of utilizing a catalytic combustor for gaseous hydrogen resulting in more efficient combustion and in turn resulting in low NOx emissions.

Challenges:
Aircraft engines have a larger operating range and so the structural design of the catalyst should be capable of bearing thermal shock and transient load cycles. The Lewis number of lean hydrogen air mixture is well below one. Thus, hydrogen diffusion is higher than the heat conduction which may result into superadiabatic wall temperatures of the catalyst. Superadiabatic wall temperatures eventually damage the catalyst in a very short time. Hence, this hard challenge needs to be seriously addressed within this project.