Retrofitting the Hydrogen Aviation Lab for hydrogen combustion: a thermodynamic analysis

In the aviation industry, hydrogen is the only option available today to achieve zero carbon emissions. However, safe utilization of hydrogen at the system level remains largely unaddressed in current research, which tends to focus on individual components rather than integrated systems. We present a feasibility analysis of hydrogen combustion in a gas turbine embedded within the Hydrogen Aviation Lab (HAL) infrastructure under realistic physical and economic boundary conditions. The novelty of this work lies in the retrofit approach to enable hydrogen combustion in an existing gas turbine with minimal changes; this avoids a full redesign of the combustion system while achieving system-level operability. The feasibility of hydrogen combustion was analyzed by modeling the thermodynamic process. The fuel-to-air ratio (FAR) was introduced as a unified control parameter that governs combustion stability, turbine entry temperature (TET), and operational safety simultaneously. At a design point representative of an auxiliary power unit (APU), a FAR of 0.016173 was identified to enable safe and stable hydrogen combustion, resulting in a hydrogen mass flow of 0.016006 kg/s; this suggests an equivalence ratio of 0.24737, which is within the margin for consistent and safe hydrogen combustion. Furthermore, the airstreams inside the combustion chamber were modified to enable more mixing of dilution air with the hot combusted air and cooling of the overall gas path air. To condition the combustion gases to the target TET of 1,293.15 K, a dilution air fraction of ε = 55.012% corresponding to an air mass flow of 2.2 kg/s was identified. The TET was fixed through APU design and material constraints. NOx emissions were deliberately excluded from this study as they were outside the defined system boundary. The results demonstrate that a feasible hydrogen combustion system can be realized through pragmatic retrofitting, which provides a foundation for further developments within integrated hydrogen aviation infrastructures.