Team

The world is undergoing strong environmental challenges that require the decarbonization of the transport sector. As such, hydrogen has been regarded as a promising fuel to power for internal combustion engines (ICE). Its carbon-free composition and relatively low-cost implementation are desirable for the energy transition. Nevertheless, hydrogen comes with its challenges.

Hydrogen flames’ natural higher adiabatic flame temperatures mean that hydrogen fuelled ICEs need to run in diluted or lean mixtures, effectively reducing the burned gas temperature and, therefore, minimize the formation of thermal NOx. In the Darmstadt Engine, an optically accessible ICE, we investigate such operating conditions. For a diluted mixture, the intake fuel-air mixture is diluted with N2, akin to an exhaust gas recirculation system of classical hydrocarbon-fuelled engines. For lean mixtures, the engine is run at various premixed lean conditions, sweeping across various equivalence ratios.

Under lean conditions, hydrogen flames are susceptible to thermodiffusive instabilities. These happen due to the higher molecular diffusivity of hydrogen relative to the mixture’s thermal diffusivity. Direct numerical simulations have predicted such instabilities to form structures of around 100 to 200 µm. As such, our work pushes the experimental setup to the limits, in order to reliably capture such structures at rates up to 8 kHz. Additionally, the flow field inside the cylinder is also captured, since the engine dynamics are so dependent on it. For diluted mixtures, cycle-to-cycle variations are more noticeable. These are mainly due to challenges in the ignition process and slower flame propagation. Therefore, early flame imaging and overall flame propagation are also studied optically. Such investigations are done through laser-based techniques like laser-induced fluorescence (LIF), particle image velocimetry (PIV) and thermographic phosphor thermometry (TPT).

Moreover, the Darmstadt Engine offers a well characterized experimental setup to build upon new ICE research. As such, experiments are also widely used for validation and development of computational fluid dynamics (CFD) models.

With the fast development of the world, including climate change and socio-economic challenges, it is important to further understand the complex engine flow and combustion phenomena. Through the above-mentioned tools and context, it is possible to achieve such objectives and consequently pave the way to a sustainable future.