In the 21st century, the desire for improved fuel efficiency of engines, lower fuel prices, and the need to reduce greenhouse gas emissions such as CO2 and NOx are leading the aviation industry to seek hybrid-electric jet engines for commercial aircraft. These aircraft will have greater maintenance challenges due to additional components requiring more reliable materials for the engine’s parts, such as turbine blades. Turbine blades must be composed of materials that have enhanced fatigue performance. Resistance to dynamic loads and high strength will be needed to ensure modern gas turbine blades are as reliable as possible. This review paper examines hybrid-electric engine turbine blades and subsequently introduces additive manufacturing (AM) and multi-principal element alloys (MPEAs) with a focus on laser powder bed fusion (LPBF), high-entropy alloys (HEAs), and medium-entropy alloys (MEAs). The tensile properties of LPBF HEAs range from 5 to 47% elongation and a UTS of 572–1640 MPa, while LPBF MEAs range from 8 to 73.9% and a UTS of 573–1382 MPa. This study focused on dynamic and fatigue properties while acknowledging gaps in high-temperature testing. The combination of mechanical properties with the ability to control internal geometry makes these AM alloys an attractive option for the next generation of gas turbine blades.

Abstract There is evidence that supersonic jet flows in astrophysics are accompanied by surrounding slow winds. This is analogous to the flow past jet engines when an aircraft is in flight. If the jet itself enters the medium under-expanded, there will be a distinct flow pattern as the wind is deflected by the diverging jet. Here, we explore the general problem of such an overpressured jet flow encompassed by a wind which is subsonic. We simulate the long-term adjustment by performing a series of hydrodynamic adiabatic gas experiments in two dimensions with cylindrical symmetry. The major result is that the oscillations in the jet induced by feedback are suppressed once the wind has swept clean the initial jet over-spill. Therefore, a slow ambient wind reduces the noise caused by the exhaust and may fully stabilise jet propagation. The differences between the shock diamonds of regular reflection and Mach discs are elucidated. In particular, with a wind, a distinctive pattern of repeated Mach shock discs occurs at high overpressures which replaces the turbulent plume. Secondly, the presence of a faster subsonic wind generates central enhanced pressure arcs and knots within each diamond. These features could provide indirect evidence for winds and are briefly discussed in terms of potential consequences for star and galaxy formation.

ABSTRACT Exposure to high-temperature surfaces accelerates the deterioration of lubricants and fuels in operation, often to the point of solid coke or sludge formation. The high operation and oil-sump temperatures of gas turbines also increase the risk of undesired oil fires which is also affected by the lubricant’s flammability. In addition, fuels used in jet engines that use regenerative cooling technology may also deteriorate due to high temperatures encountered before entering the combustion chamber. The present work explores the effect that thermal and oxidative degradation, caused by exposure to high-temperature surfaces, has on the ignition characteristics of a turbine lubricant, a motor oil (Castrol GTX 20W-50), and JP-5. All three hydrocarbons were exposed to high-temperature surfaces, up to 573°C (and bulk fluid temperatures between 137°C and 247°C), under a controlled inert or oxidative environment which resulted in the formation of solid coke or sludge deposits. Oil and fuel samples collected at the end of the aging cycles were then injected into a shock tube using a custom endwall injection method to study their ignition delay time (IDT). It was found that the aging process decreased the fluids’ activation energies when aged in an inert environment but appears to increase the values when aged in an oxidative environment. The resulting activation energies were in the range of 26–58.7 kcal/mol for the lubricants and 42–64.2 kcal/mol for JP-5.

Abstract To address the issues of severe noise pollution and high carbon emissions associated with turbine engine propulsion systems used in previous generations of supersonic technology, this study proposes the ammonia decomposition turbine-less SOFC/supersonic jet engine hybrid system (NH 3 SOFC/SJE system). The proposed design aims to achieve supersonic cruising, transoceanic flight, and zero-carbon emissions, offering a sustainable solution for next-generation supersonic propulsion systems. The results indicate that as the pressure ratio increases, specific thrust continues to rise, while the fuel consumption rate initially decreases and then increases. The optimal pressure ratio is found to lie between 15.1 and 19.8. Higher fuel utilization efficiency contributes to the improved performance of the hybrid system. When the ammonia decomposition temperature is around 900 K, both the fuel economy and propulsion performance of the hybrid system are effectively met. The hybrid system achieves the most economical cruising state at an altitude of 20 km and a Mach number of 1.8. In this optimal cruising state, the Cost per unit distance of the conventional turbojet engine is 39.9% higher, while that of the H 2 SOFC/SJE system is 6.03% higher compared to the proposed system. In summary, ammonia, as a zero-carbon fuel, offers significant advantages for supersonic flight.

The article discusses the features of design and technological preparation of such complex-profile products of small-size turbojet engines as the compressor wheel and turbine wheel, obtained by the method of 3D-printing. It describes the bottlenecks of the currently used additive technology and proposes ways to resolve them. These solutions are divided into two groups. The first includes special design elements incorporated into the 3D-model for printing, and the second involves the peculiarities of the mechanical post-processing technology for complex profile surfaces. The first part of the article examines design elements for compensating negative thermal effects, special support structures, elements for subsequent precise basing on a five-axis CNC machine, and allowances for post-processing. The second part demonstrates the post-processing technology, including the preparation of technological bases on a universal machine, CAD preparation of the processing project, selection of tools, fixtures, and cutting modes, and achieving a finished blade profile on a five-axing milling machine. The conclusion discusses the qualitative and quantitative results: comparing the time of manufacturing the product entirely by mechanical means with the proposed method, presenting the results of roughness measurement of critical surfaces, and conclusions about the applicability of the proposed approach.

Full-cycle self-sustaining wireless jet engine shaft monitoring via rotor-conformal thermoelectrics

The transition toward sustainable aviation fuels requires dedicated experimental platforms capable of evaluating alternative fuels under realistic propulsion conditions. This study presents the development and laboratory experimental validation of a modular testing installation designed for sustainable fuels derived from plastic waste pyrolysis, intended for aerospace engine applications. The proposed system is conceived as an integrated small-scale gas turbine assembly that reproduces the functional characteristics of a jet engine and enables controlled laboratory investigations of dynamic behavior, combustion stability, and performance. The installation comprises a compressor, annular combustion chamber, and turbine mounted on a common shaft, along with a fully autonomous fuel supply system equipped with electronically controlled pumping, safety devices, and thermal conditioning of the fuel mixture via an attached Stirling engine. Combustion processes are continuously evaluated using an exhaust gas analysis system to assess fuel composition and combustion quality, while a high-speed camera operating at 50,000 fps enables detailed visualization of flame stability. Operating parameters, including temperatures, pressures, rotational speed, mass flow rates, and thrust, are monitored and recorded through an integrated control and data acquisition system with real-time analysis capabilities. Experimental results demonstrate stable operation and reliable ignition using alternative fuel mixtures, confirming the suitability of the modular installation as a versatile research platform for the assessment and comparative analysis of sustainable aerospace fuels.

The paper presents a theoretical analysis of possible thermodynamic cycles of a pulse jet engine. To clarify the type of thermodynamic cycle, equations for calculating the polytropic index from instantaneous gas parameters in the combustion chamber are derived. The classic Argus As 014 valved pulse-jet engine workflow, both at static conditions and at 800 km/h, has been simulated. The simulation results confirm the known data that the real operating cycle of a valved pulse jet engine during static conditions is the Lenoir cycle. However, for the engines with straight air intake and with increasing flight speed, the specific workflow nature, i.e. the presence of polytropic pre-compression before heat release, that corresponds to the Humphrey cycle rather than the Lenoir cycle, has been found. Unlike a straight intake engine, a valved pulse jet engine with a side air intake that does not have air pre-compression has also been found to exhibit increased performance with increasing flight speed. The obtained data confirm that, in general, the thermodynamic cycle of a valved pulse jet engine can be represented as the Humphrey cycle, which in specific cases, such as zero flight speed and/or a side air intake, does not experience polytropic pre-compression before heat release and corresponds to the Lenoir cycle.

Abstract Repairing is considered as a practical and economic scheme to effectively extend the lifetime of components made of Inconel 738 (IN 738), which has been widely used in hot sections of jet engines and industrial gas turbines. In this study, the feasibility of repairing IN 738 substrates was investigated using InterPulse tungsten inert gas (TIG) welding with Inconel 625 (IN 625) and Pmet 838 as feeding materials. It was shown that single-pass deposition achieved a sound metallurgical bonding under three different TIG parameters, with no cracks observed in any of the specimens. Under multi-pass repairing, γ′ dissolution was observed in the heat-affected zone (HAZ), and cracks were observed neither in the multi-pass deposited layers nor the HAZ. The Pmet 838 deposited layer was quasi-homogeneous and entirely devoid of γ′; the IN 625 multi-pass deposited layer, however, exhibits pronounced mesoscopic segregation with significantly lower hardness than the IN 738 substrate. The Pmet 838 deposited layer demonstrates considerably higher hardness than that of the IN 738 substrate, primarily attributed to the existence of dense cellular structures. The hardness in the HAZ of both specimens decreases with increasing the distance from the fusion line to the base metal, which may be associated with gradient variations of the cellular structures. After annealing at 920 °C for 150 h, the average Vickers hardness of the Pmet 838 multi-pass deposited layer decreased from 486.1±13.9 HV 0.2 to 378.2±6.2 HV 0.2 , even though copious precipitation of γ′ was observed in it, which is attributable to the disappearance of the cellular structure; in contrast, the IN 625 deposited layer exhibited heterogeneously distributed γ′ precipitates and needle-like δ phase, corresponding to the aforementioned mesoscopic segregation, resulting in an increase in the average Vickers hardness from 252.1±6.6 HV 0.2 to 317.6±17.4 HV 0.2 .

When a jet engine starts, the temperature starts to increase within a range. At various durations of the engine run, there is some temperature. Higher the thrust, higher the heat. This temperature is called Exhaust Gas Temperature. Each type of engine has a maximum allowed exhaust gas temperature and the difference between the actual gas temperature and the maximum temperature is called the Exhaust Gas Temperature Margin. Airlines struggle to know which components should be replaced to obtain desired Exhaust Gas Temperature Margin. Formula for EGT Margin is EGT Margin = EGT Red Line – EGT Take off. Every airline aims to obtain a margin as high as possible. If the margin is very low, it is unsafe to use the engine and it could lead to fire in the engine. The article explains the root cause of lower margin, factors impacting the margin, what can be done to maintain a good margin and what must be avoided at all costs for the safety of the aircraft engine. Currently, there are no directions or guidelines on what engine components can be replaced to improve EGT Margin. The article shows how the simulation data was captured and what methodology was used to obtain the data.

Currently the kerosene fuel is very important for use in the heating, cooking, and fuel of the jet engines. The study aims effected of mixing different lite bit and same of gasoil to three different type of kerosene samples, and study the initial boiling point (IPB) during of distillation test. This study focused on targeting the IPB of the kerosene samples by finding the specific gravity (Sp.gr) test, the American Petroleum Institute (API) degree, and distillation test. However, these samples of kerosene were characterized and labeled (kero-01, kero-02, and kero-03, respectively) before the dealing processes, while the samples after the adding processes were labeled (kero-11, kero-12, and kero-13, respectively). The results showed that the IBPs were reached 151 °C, 161 °C, before, and after blending processes respectively. Then study addition percentage (5 to 95 %) of gasoil to kerosene was affected to the IPB. The addition rate showed that the increase was approximately 8 % of the boiling point. Finally, via finding sp.gr, API degree and distillation of final products it was found that the mentioned mixing ratio was very small, yet it was effective in examining the IPB in the distillation test during this work.

The progressive incorporation of sustainable aviation fuels to achieve zero emissions in 2050 in the aviation industry implies the evaluation of properties and compatibility of these new fuels with the fuel injection systems existing in current aircraft. Although lubricity is more critical for fuels used in compression ignition engines, in small turbojet engines lubrication fluid is directly blended with fuels, which makes mandatory the good lubricating behavior of kerosene-lube oil blends. For this reason, apart from evaluating lubricity of neat alternative jet fuels, two additives are selected for this study. One is a typical synthetic lube oil used in this type of jet engine, and the other is a biodiesel renewable fuel known for its good lubricating properties. Results show similar results of wear scar diameters of neat kerosene fuels, with a clearly abrasive wear. The incorporation of these additives improves notably the lubricity, biodiesel being more effective than lube oil, appearing as a tribocorrosive wear when this renewable additive is used. The improved lubricating properties of biodiesel and kerosene blends open the possibility of replacing the lubricating oil added to small turbojet engines or directly using these blends in reciprocating engines used in light aircraft or unmanned aerial vehicles. Furthermore, this study has developed a comparison between the ball on cilinder lubricity evaluator and high frequency reciprocating rig methodologies (HFRR), results indicating a higher lubrication with biodiesel blends in HFRR tests.

Rare-earth zirconates against environmental silicate corrosion in jet engines

ABSTRACT The efficiency of a jet engine heavily depends upon the efficiency of its compressor. This study investigates the impact of leading‐edge tubercles on a transonic axial compressor. For this purpose, a CFD analysis has been performed for NASA Rotor 37. The method of investigation is based on the numerical solution of steady‐state, three‐dimensional Navier–Stokes equations using k‐ ω ‐SST (Shear Stress Transport) turbulence model. The accuracy of simulations is ascertained by comparing the numerical data with the available experimental data. Several configurations are considered by changing different tubercle parameters: amplitude, wavelength, and span‐wise location of the tubercles on the rotor blade. The results indicate an increase in efficiency for all the configurations considered for the modified rotor as compared to the corresponding baseline rotor with a maximum increase of 0.52%. The improvement in efficiency can be attributed to the higher outlet pressure achieved by the modified blade, which is 1.91% greater than that of the baseline blade. Mach number contours show that the location of the shockwave has been moved further downstream in the optimized case. Furthermore, new vortices are observed to be generated near the middle of the chord on the suction side of the tubercle model. Vortices formation has resulted in the redirection of the surrounding flow in an axial direction. Simultaneously, it has also contributed to loss which is associated with temperature increase. However, pressure gain at the outlet accomplished by redirection of flow outweighs the drawbacks of loss associated with temperature increase thus reducing the overall losses.

Transmittance of Gaussian beam in anisotropic jet engine exhaust turbulence

Altitude-based CFD investigation of hydrogen combustion behavior in a jet engine combustor using real operational data

Abstract In a medium experiencing non-Kolmogorov jet engine exhaust turbulence, signal-to-noise ratio ( SNR ) is evaluated. SNR is naturally degraded due to the presence of turbulence. The reduction in the SNR in non-Kolmogorov jet engine exhaust turbulence is calculated and presented with respect to the power law for various wireless optical communication link and turbulence parameters. The reduction in SNR is referenced to the SNR achieved in the link when there is no turbulence. SNR , being an important entity in determining the link performance, knowledge about the reduction in SNR will help the designers of wireless optical communication links, especially installed in airport environments where jet engine exhaust turbulence mostly occurs.

Combustion-generated nanoparticles with diameters of 10-200 nm are ideal shuttles to transport compounds into the human body. The so-called Trojan Horse effect describes the translocation of persistent nanoparticles covered with adsorbates across the alveolar membrane of the lung to the blood circulation system and further to other organs. The toxicology of such nanoparticles is determined by the chemical nature of their adsorbates. We determined the genotoxic potential of such nanoparticles and quantified levels of carcinogens and mutagens like polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, polychlorinated dibenzodioxins (PCDDs) and furans (PCDFs) in diesel, gasoline and jet engine exhausts. We studied the impact of catalytic particle filters on these compounds which can bind to the aryl-hydrocarbon receptor (AhR), an important domain of a human transcription factor reaching the cell nucleus, where it interferes with gene transcription and regulation.

Maintaining a consistent quality of TiAl4822 blades used in jet engines is crucial, even when compositional variations occur during production. This study investigates the optimal Al and O concentration ranges that yield favorable practical properties. Additionally, the feasibility of reusing machining chips as a low-cost melting feedstock is explored. The results indicate that both impact resistance at 25 °C and machinability remain unaffected or even improve at O concentrations up to at least 0.13 wt%. Moreover, materials containing 0.13 wt% O exhibit the widest optimal range of Al concentrations (46.8–47.4 at%), but was narrower at lower or higher Al concentrations. The influence of the α2-phase ratio on impact resistance is substantially greater than that of O concentration, with the optimal range being 0.2–0.3. Furthermore, a new pre-treatment method is developed to reuse machining chips containing large amounts of water-soluble cutting oil. This method involves removing C through atmospheric heating after ultrasonic cleaning using acetone. Furthermore, TiAl4822 castings including these preprocessed chips exhibit superior properties compared with those of chip-free low-O materials, despite the higher O concentration. These findings demonstrate that moderate O enrichment is tolerable, and even beneficial, enabling cost-effective recycling in TiAl4822 blade production.

Accurate identification of defects in Jet Engine Turbine and compressor blade surface plays a vital role in ensuring engine efficiency, safety and secure life. Traditional detection techniques were manual and consumed more time, error prone and need of specialized experts. To address these challenges, this work proposes an automated defect detection system using Swin Transformer Based Deep learning model. High resolution blade surface images were captured, pre-processed and augmented to improve robustness with varying surface condition. The novelty of the proposed work is that it adapts the Swin Transformer architecture to the specific challenges of turbine and compressor blade surfaces and it can detect micro-scale defects with high fidelity, by detecting both local and global features. Experimental results demonstrated that the proposed Swin transformer model produces high detection performance compared to the conventional CNN model with an accuracy of 98.4%, precision of 97.9%, recall of 98.7%, F1-score of 98.3% and mean Average Precision (mAP) of 97.6% on a dataset consisting of 172 high-resolution turbine and compressor blade images. The performance of the proposed method indicate that Swin Transformer model is an efficient tool for Non-Destructive Inspection of jet engine turbine and compressor blade surface which can be integrated into automated maintenance systems for better reliability and minimized operational risks.