Hydrogen-Based Intrinsic-Flame-Instability-Controlled Clean and Efficient Combustion

Chemical energy carriers will play an essential role for future energy systems, where harvesting and utilization of renewable energy occur not necessarily at the same time or place, hence long-time storage and long-range transport of energy are needed. For this, hydrogen-based energy carriers, such as hydrogen and ammonia, hold great promise. Their utilization by combustion-based energy conversion has many advantages, e.g., versatile use for heat and power, robust and flexible technologies, and its suitability for a continuous energy transition. However, combustion of both hydrogen and ammonia is very challenging. For technically relevant conditions, both form intrinsic, so-called thermo-diffusive instabilities (very different from the often-discussed thermo-acoustic instabilities), which can increase burn rates by a stunning factor of three to five! Without considering this, computational design is impossible. Yet, while linear theories exist, little is understood for the more relevant non-linear regime, and beyond some data and observations, virtually nothing is known about the interactions of intrinsic flame instabilities (IFI) with turbulence. Here, rigorous analysis of new data for neat H2 and NH3/H2-blends from simulations and experiments will lead to a quantitative understanding of the relevant aspects. From this, a novel modeling framework with uncertainty estimates will be developed. The key hypothesis then is that combustion processes of hydrogen-based fuels can be improved by targeted weakening or promotion of IFI, and that this kind of instability-controlled combustion can jointly improve efficiency, emissions, stability, and fuel flexibility in different combustion devices, such as spark-ignition engines, gas turbines, and industrial burners. Guided by the developed knowledge and tools, this intrinsic-flame-instability-controlled combustion concept will be demonstrated computationally and experimentally for two sample applications.