Abstract Hydrogen is a promising energy carrier for reducing the carbon footprint of next-generation propulsion systems, but its practical deployment requires engines capable of operating safely and efficiently under relevant conditions. While Large-Eddy Simulations (LES) of hydrogen flames are well established in academic configurations, their use at elevated pressure remains challenging due to computational resources and the scarcity of validated turbulent combustion models. This work presents a LES investigation of hydrogen multi-regime flames under engine-like conditions and assesses the performance of existing combustion models in this regime. A dual-swirl hydrogen injector experimentally studied at IMFT and ONERA is simulated using the compressible LES flow solver AVBP (https://avbp-wiki.cerfacs.fr/) from CERFACS. Simulations are conducted at atmospheric and elevated pressures, covering four operating conditions with different flame topologies, Reynolds numbers ranging from 2,800 to 390,000, air injection temperatures up to 460 K, and pressures up to 12 bar. Combustion is modeled using a semi-detailed chemical mechanism coupled with a thickened-flame approach, with targeted mesh refinement applied to the high-pressure cases. LES results show excellent agreement with experimental flow measurements at atmospheric pressure and good agreement with flame visualizations at elevated pressure, supporting the applicability of the modeling strategy to high-pressure hydrogen combustion. The combined effects of pressure and Reynolds number on flame structure are further examined by separating premixed and diffusive reaction contributions, providing new insight into their structures and the impact of turbulence under engine-relevant conditions. A preliminary assessment of NOx formation is also provided, highlighting the effect of pressure and strain rate on key thermochemical precursors, while flow residence times remain comparable at atmospheric and high-pressure conditions.
Abstract Dust-laden environments cause substantial propeller erosion, leading to decreased performance and lifespan. The first part of this study examines the flow characteristics and performance of the SR-5 high-speed propeller, which features ten thin, swept blades rotating at 5,709 rpm. The second part investigates particle dynamics within the propeller, impact conditions, and the progression of erosion during cruise and takeoff. The analysis demonstrates the effects of operating conditions, propeller setting, particle type (dust or sand), and concentration on erosion. Particle trajectories and erosion were calculated using a Lagrangian-based finite element procedure, enabling precise tracking and determination of impact conditions. Particles were generated and released randomly to replicate the particle size distribution and concentrations typical of desert environments. Erosion rates were quantified using a semi-empirical erosion correlation specifically developed for composite materials. The dynamic behavior of particles and their impacts, as well as the resulting erosion, are influenced by the particle type and the propeller's operating conditions. The leading edge (LE) and pressure side (PS) of the blade were exposed to a dense, high-velocity particle flux, impacting and eroding almost the entire PS, while the front of the suction side (SS) was impacted by particles of high velocities and angles of attack. The depth of wear was assessed for different particle types, concentrations, and operating conditions. The present results, particularly the correlations established between erosion wear and propeller dimensions, can help manufacturers and operators of high-speed propellers develop solutions to limit erosion progression.
High-pressure hydrogen storage requires up to 700 bar to achieve sufficient volumetric energy density, with reciprocating compressors preferred for their high flow capacity and oil-free operation. Meeting purity requirements while handling hydrogen's low molecular weight, high pressures, and dry seals presents major challenges for sealing elements. As a result, nonlubricated compressor technology must extend beyond conventional API 618 applications. Predicting leakage, piston ring wear, and seal performance under nonlubricated conditions is therefore essential to ensure the reliability, efficiency, and safety of hydrogen compression systems. To address these challenges, a dedicated test campaign was developed to evaluate sealing performance under representative operating conditions using a unique setup. The setup features a special single-acting, nonlubricated cylinder mounted on a vertical compressor operating with helium at pressures above 200 bar. Extensive instrumentation was implemented, including 45 dynamic pressure probes positioned along the cylinder liner to capture instantaneous pressure profiles in the gaps between seals, piston, and liner, as well as six dynamic pressure probes positioned along the pressure packing. Since fixed sensors measure within a moving volume, a tailored procedure was established to reconstruct pressure signals inside the moving gaps. The results reveal how pressure drop is distributed among sealing elements throughout the compression cycle, depending on the operating conditions, and highlight the distinct operating principles of different seal typologies.
Abstract The use of hydrogen as an energy carrier has gained increasing relevance in recent decades, driven by the need for a reliable, demand-centered energy and heat supply. In this context, decentralized combined heat and power (CHP) systems have become prominent due to their high overall efficiency and the relatively small amount of hydrogen required for operation, which can be produced locally. micro-Gas Turbines (mGTs) have emerged as a preferred option for these systems because of their high load capacity, fuel flexibility, and low maintenance requirements. However, 100% hydrogen combustion in mGTs presents significant challenges, primarily due to high inlet temperatures caused by exhaust gas heat recovery. These challenges arise from hydrogen's characteristic properties, such as its wide flammable range and low self-ignition characteristics. If not carefully managed, these factors can compromise the structural integrity of the mGT and thus should be carefully evaluated in the burner's analysis. In this regard, the mGT F400S.3 combustor, developed by the German Aerospace Center (DLR), enables 100% hydrogen operation through a jet-stabilization concept. This study presents a high-fidelity large eddy simulation (LES) analysis of the burner, first under atmospheric conditions and subsequently under pressurized conditions representative of real mGT operation. Turbulence–chemistry interaction is modeled using an extended Thickened Flame (TF) approach. Atmospheric LES results are compared against experimental OH*-chemiluminescence data, showing good agreement in terms of flame shape and liftoff height. Building on the validated atmospheric setup, the numerical framework is consistently extended to pressurized operation, demonstrating stable 100% hydrogen combustion without auto-ignition or flashback, despite the challenging combination of high inlet temperature and pressure: the results provide insight into flame stabilization behavior in a micro-Gas Turbine operating regime.
Natural Gas/Ammonia (NG/NH3) fuel blends are a promising route to reduce CO2 emissions from gas turbines while leveraging existing NG infrastructure, but their auto-ignition behavior at elevated pressures is not yet well constrained. This work reports high-pressure shock tube ignition delay time (IDT) measurements for NG/NH3/Air mixtures at gas turbine-relevant conditions. Experiments were performed at pressures of 5, 10, and 25 bars, temperatures from 1500 to 2100 K, with equivalence ratios of Phi = 1.0, 1.2, and 1.4, and argon-diluted fuel compositions spanning pure NH3 to NG-rich blends. Experiments were carried out in two shock tube facilities at the University of Central Florida, with ignition being monitored via OH* emission chemiluminescence. The experimental data is compared against simulations using a widely employed nitrogen chemical kinetic mechanism from Glarborg et al., a mechanism by the CRECK modeling group, and a newly developed University of Central Florida (UCF) NG/NH3 mechanism. Across all mixtures, IDTs decrease monotonically with increasing temperature and pressure. Increasing pressure from 5 to 10 and 25 bars reduced IDTs for similar temperatures by up to 40% and 60%, respectively, depending on mixture composition. The addition of natural gas (NG) substantially shortens the IDT relative to pure NH3, with the largest incremental benefit at the lowest NG fractions and diminishing returns at higher NG fractions. The pressure sensitivity of ignition is strongest for NH3-rich mixtures and weakens as the NG fraction increases, while changes in equivalence ratio have a comparatively modest effect over the range of Phi = 1.0-1.4. The mechanisms reproduce the overall temperature and composition trends but show systematic deviations for NG-rich mixtures and some disagreements at specific pressure and temperature points in NH3-rich mixtures. Sensitivity analyses based on OH* production indicate that ignition is primarily controlled by CH3 and C2 radical chain-branching pathways in mixtures with NG, while NH3 chemistry mainly influences ignition through radical scavenging and NOx-forming channels. The present measurements provide new high-pressure validation targets for NG/NH3 kinetic mechanisms and help identify specific reaction classes that require further refinement for predictive simulations of low-carbon gas turbine combustion.
