Search Results (543)

This work presents the thermodynamic design and performance assessment of an integrated process line for the separation, liquefaction, storage, and valorization of carbon dioxide (CO₂) and nitrogen (N₂) from flue gas streams. The proposed system aims to combine carbon capture with cryogenic energy storage by exploiting the thermophysical properties of the main flue gas constituents. A representative flue gas derived from complete methane combustion (9.5% CO₂, 71.5% N₂, and 19% H₂O by volume) is considered as the feed stream. The process is developed and simulated in DWSIM v9.0.5, adopting a steady-state mass and energy balance framework coupled with rigorous thermodynamic modeling of phase equilibria and unit operations. The plant configuration is based on sequential cooling, compression, and expansion stages, enabling the selective condensation of H₂O, CO₂, and N₂ at different temperature levels. The system integrates heat exchangers, compressors, pumps, turboexpanders, phase separators, and cryogenic storage tanks, while a portion of the liquefied CO₂ is reused as an energy carrier through vaporization and expansion in a dedicated turbine. The results demonstrate that the process achieves a CO₂ capture ratio of 81.7%, with a specific electric consumption (SEC) of 10.44 kWh/kg_CO2 and 1.71 kWh/kg_N2. The overall net electric demand is 1.29 kWh/kg of treated flue gas, while the round-trip efficiency (η_RT,CO2) is 18.6%. A significant amount of energy can further be recovered from the “waste” exhaust water stream (12.94 kg_L-H2O/kg_flue-gas, at 91 °C and 1.2 bar) up to 800 Wh/kg_flue-gas, improving the performance of the entire process (SEC_CO2: 3.86 kWh/kg_CO2, η_RT,CO2: 69.8%). The study confirms the thermodynamic feasibility of the proposed configuration and identifies nitrogen liquefaction as the dominant energy-intensive step. Future optimization efforts should therefore focus on reducing exergy destruction in the deep cryogenic section through improved heat integration, enhanced cold-energy recovery, optimized compression–expansion staging, and reduced pressure losses. Full article

In spite of the intense research interest in the integration of Pressure Gain Combustion (PGC) systems with a turbomachinery module, limited studies have been conducted regarding the experimental investigation of the strong spatio-temporal perturbations of these unconventional machines’ outflow. This paper focuses on experimentally characterizing the perturbing exhaust flow of a Constant-Volume Combustor (CVC). Preceding numerical analysis offers a transition duct able to attenuate the CVC’s produced unsteadiness and connect this PGC with a turbomachinery module. In fact, the transition duct is manufactured, while a pair of windows are introduced allowing for high-frequency Particle Image Velocimetry (PIV) analysis. In addition, fast-response pressure sensors in the combustion chamber, upstream and downstream of the transition duct, are implemented. A parametric analysis of the rotational frequency of the inlet–outlet rotary valve pair is conducted. The perturbing outflow of this PGC is characterized and experimentally visualized for the first time. Moreover, the attenuation performance of the transition duct on the CVC’s produced unsteadiness is evaluated for different cycle frequencies. The transition duct is proved to be able to alleviate the spatial and time-dependent unsteadiness by CVC, offering crucial evidence and conclusions for the future industrial integration of the CVC with a High-Pressure Turbine stage. Full article

Thermoacoustic instability remains an important challenge in gas turbines. In can-annular combustors, cross-talk effects can lead to complex collective dynamics. This paper investigates the in-phase synchronization of low-frequency thermoacoustic oscillations in a can-annular combustor, focusing on the upstream cross-talk mechanism mediated by the compressor combustion casing. Dynamic pressure data from the full-scale engine reveal a transition from independent, low-amplitude pressure dynamics to a state of high-amplitude, in-phase synchronized oscillation in the combustor system. To quantify the upstream cross-talk effect, the multi-port acoustic scattering matrix of the casing is computed by solving the Helmholtz equation based on a mean-flow field obtained from Reynolds-Averaged Navier–Stokes simulations. Analysis of the matrix shows that the casing provides a coupling path between cans, with strength and phase being insensitive to the relative azimuthal position of the cans. Based on this physical insight, a star-network model of coupled Van der Pol oscillators is developed. The model, with parameters identified from experimental data and inferred from the scattering matrix, successfully reproduces the synchronization phenomenon observed in the experiment. A subsequent parametric study based on the validated model shows that in-phase synchronization occurs within periodic windows of the time delay and that the range of these windows expands with increasing coupling strengths. For $\tau =0.1T$, $0.85T$ and $1.1T$, synchronization is achieved with moderate coupling strengths. For $\tau =0.35T$ and $0.6T$, the interaction between the two coupling mechanisms suppresses synchronization even at strong coupling strengths. This study shows that the upstream cross-talk effect is an important mechanism for in-phase synchronization and provides a validated, physics-based model for analyzing and predicting the collective thermoacoustic behavior of can-annular combustors. Full article

To mitigate the effects of climate change, the world must significantly reduce its reliance on fossil fuels to lower greenhouse gas emissions. The nuclear power and renewable energy sources, such as solar, wind, water, waste, and geothermal energy, emit minimal to no greenhouse gases or pollutants during operation. These sources are considered crucial for combating climate change and supporting sustainable development. However, the production of electricity, like most industries, generates waste. Comparisons show clear differences: fossil fuel plants produce the largest total waste mass (primarily combustion ash, flue gas desulfurization residues, and wastewater sludge), while nuclear facilities generate a minimal volume but high-activity spent fuel and long-lived radioactive materials. Solar PV systems generate significant end-of-life electronic waste and glass encapsulant, and wind turbines yield moderate composite blade residues. Hydropower sediment management and geothermal scaling contribute unique waste streams of local concern. Regardless of the energy source, responsible waste management is critical to minimize environmental impacts. This article explores the sustainability of low-carbon energy sources, specifically focusing on waste management with the aim of highlighting the need of implementing targeted strategies such as advanced recycling and material substitution in order to minimize environmental impacts and enhance the circularity of low-carbon energy systems. Full article

The aviation sector is accelerating the transition toward low-carbon propulsion, and Sustainable Aviation Fuels (SAFs) represent a key leverage to reduce lifecycle emissions without modifying existing turbine architectures. Microturbines offer an effective and low-cost platform for assessing SAF behaviour under engine-representative conditions. In this work, a zero-dimensional performance and emission model of the GTM-140 microturbine was developed in GSP and validated against experimental data at 70,000–112,000 rpm for Jet A-1 and HEFA paraffinic blends. The model reproduces thrust and fuel-flow trends with good fidelity, with deviations typically below 6% across all operating points. Introducing 50% HEFA consistently reduces fuel consumption, leading to a TSFC decrease of 3–6%, with the strongest effect at high rotational speed, where compressor efficiency is highest. CO emission indices decrease by 6–9% at mid-load and converge at full power due to enhanced oxidation, while NO_x increases by 6–15%, driven by the higher adiabatic flame temperature associated with HEFA’s increased H/C ratio and heating value. These results confirm that simplified 0D modelling can reliably capture performance and emission trends of SAF-fuelled microturbines and demonstrate the dual effect of HEFA: improved combustion efficiency and CO reduction, at the expense of moderately higher NO_x formation. Full article

The high-temperature corrosion (HTC) caused by H₂S poses a critical threat to the water-wall of unity boilers. To address this challenge, the present work develops a predictive corrosion depth model that integrates two critical determinants: the local concentration of H₂S and the temperature of the water-wall metal. The proposed methodology is applied to evaluate HTC risks under three distinct thermal loads: boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA) and 50% THA. Furthermore, the protective effect of near-wall air (NWA) ratio injection using recirculated flue gas (RFG) was numerically investigated, to quantify their influence on both HTC mitigation and in-furnace combustion characteristics. Key findings indicate that at BMCR load, elevated sidewall temperatures combined with H₂S enrichment produce a peak corrosion depth of 33.7 μm. At 50% THA, the peak H₂S concentration drops sharply to 150 ppm, and the corresponding corrosion depth falls to only 7 μm. Consequently, it is recommended that NWA protection measures be implemented whenever the boiler load exceeds 50% THA. Even at a 7% NWA ratio, the impact on the furnace temperature field remains negligible. Meanwhile, it significantly reduces the corroded area and halves the peak corrosion depth, confirming that RFG-based NWA offers a flexible and effective engineering solution for mitigating HTC in coal-fired utility boilers. Full article

This paper presents a conceptual design for a technological installation aimed at mitigating ventilation air methane (VAM) from coal mine exhaust shafts, offering combined heat and power generation. It addresses the challenge posed by low methane concentrations (below 0.7%), which preclude direct combustion. To overcome this, the proposed concept involves diverting a portion of the VAM to a combustion chamber of the power boiler dedicated to co-combustion with flotation concentrate suspension, which is properly prepared for feeding into the combustion chamber. The heat generated in the power boiler produces steam to drive a turbine generator for electricity production. Back-pressure steam from the turbine can be utilized for district heating or as a thermal energy source for various industrial processes, optimizing the plant’s energy efficiency and reducing its environmental footprint. The feasibility of this technology hinges on its cost-effectiveness and energy efficiency. This aspect of efficiency has been outlined. An energy balance analysis, based on real emission data from a selected mine, is provided to determine power boiler efficiency, fuel consumption, and a VAM reduction rate. The forecast of the amount of energy produced was presented for a single installation with a grate boiler capable of co-firing fuels with a VAM flow participation of 25 m³/s. Such installations can be scaled to meet mine requirements, enabling the neutralization of VAM at a total capacity of up to 300 m³/s, which corresponds to emissions from a large ventilation shaft. Full article

Replacing traditional hydrocarbon fuel in aircraft turbine engines with hydrogen fuel contributes, in line with current trends, to reducing harmful carbon dioxide emissions and enabling increased flight altitude. Given the high research costs of full-scale turbine engines, research on miniature turbojet engines, due to their availability and relatively low modification costs, can play a significant role in better understanding and developing concepts for adapting existing hydrocarbon-based fuel systems to hydrogen fuel. This article presents the results of a comprehensive numerical analysis of the hydrogen combustion process—illustrating changes in its location and structure—for multiple variants of design changes to the combustion chamber of the miniature GTM-140 turbojet engine, primarily involving appropriate shaping of airflows through the holes in the glow tube and the location of the hydrogen injection point. Based on this analysis, a modernized combustion chamber geometry was proposed, which should ensure a stable hydrogen combustion process that is safe for the thermal resistance of the structural material—and structurally comparable to the baseline Jet-A1 hydrocarbon fuel combustion process. The obtained results can give ground for the construction and experimental testing of a hydrogen-powered turbine engine. Full article

Contrail emissions are aviation’s largest non-CO₂ contribution to global climate change. According to the Schmidt–Appleman criterion, potential future aircraft propulsion systems may enhance contrail formation relative to conventional engines through three mechanisms: (1) increased overall efficiency, (2) the use of hydrogen as fuel, and (3) external cooling in low-temperature fuel cell propulsion systems, which is the most critical factor. This paper presents the thermodynamic background and a system concept for contrail prevention applicable to conventional gas turbines, hydrogen combustion, and fuel cell propulsion systems. First, it is shown that fuel cell propulsion and hydrogen combustion exhibit equivalent thermodynamic contrail propensity when fuel cell exhaust is mixed with cooling air, analogous to core–bypass mixing in a conventional turbofan engines. Second, contrail mitigation via controlled condensation of exhaust water vapor is analyzed. It is demonstrated that the required cooling for LT-PEM fuel cell systems is 3–5 times lower than for turbofan engines, due to the already extensive thermal management in fuel cells. Since contrail avoidance is only necessary in ice supersaturated regions, a control scheme is proposed that limits condensation to the minimum required amount of water, thereby significantly reducing the overall drag impact. Avoiding contrail formation could provide a substantial climate benefit for future propulsion architectures. Full article

Liquid rocket engine injectors play a fundamental role in determining combustion efficiency, stability, and overall propulsion performance. This review paper provides a comprehensive analysis of liquid-injector technologies used in space propulsion systems, with emphasis on their historical evolution, atomization mechanisms, and cross-domain insights from aviation fuel injection systems. The study begins by examining the fundamental processes governing liquid jet breakup, including primary and secondary atomization, ligament formation, and droplet generation, together with the non-dimensional parameters that control these phenomena. The historical development of injector architectures -from early orifice-based and impinging designs to modern coaxial and pintle configurations—is then discussed in relation to increasing performance requirements and combustion stability challenges. A comparative perspective with aviation gas turbine injectors is introduced to highlight similarities in atomization physics and differences in operating conditions and design constraints. The paper also reviews experimental and numerical approaches used to characterize spray formation and injector performance. The results indicate that injector geometry and flow conditions strongly influence mixing efficiency, droplet size distribution, and combustion–acoustic coupling mechanisms. The study concludes that integrating cross-domain knowledge and modern design techniques is essential for advancing injector performance in next-generation propulsion systems. Full article

Efficiency improvements in gas turbines have been realized in recent decades by raising the turbine inlet temperature. This work devotes attention to pressure-gain combustion (PGC), which is a technology capable of yielding the same time-averaged combustor outlet temperature as conventional Brayton–Joule cycles but at a higher pressure. Here, PGC is implemented in a thermodynamic cycle wherein the compression system operates at a lower pressure ratio compared to the reference Brayton–Joule cycle. Focusing on E-, F- and H-class gas turbines, representative of three different technologies, the possible PGC advantages in both simple- and combined-cycle modes are investigated by means of in-house simulation code. Specifically, this work includes the energy penalty related to the PGC system cooling in the cycle analysis. In detail, the effects of different coolant amounts on the PGC system, as well as the lower efficiency at the first expansion stage compared to conventional gas turbine systems, are analyzed. Among the three classes of gas turbines, E is the one wherein the advantages are more significant, with ultimate efficiency values in simple-cycle mode calculated in the range of 38% to 41%. The higher the gas turbine technology and power class, the lower the benefit, and current H-class gas turbines already start from a higher efficiency level. Anyway, focusing on the latter, performance improvements for the PGC combined cycle seem to be possible, with efficiency greater than 65%, exceeding the current state-of-the-art systems. Full article

In the current environmental and political scenario, hybrid vehicles play crucial roles in the transition to sustainable mobility. The role of internal combustion engines (ICEs) is also of utmost importance to comply with the even more stringent emissions regulations. To that end, also considering the need for increased power density in ICEs, turbocharging allows for improved performance and reduced emissions. Within this context, the present paper introduces the novelties of a patented turbo compound layout with supercharging capabilities, i.e., the Turbo Generator Electric Multistage Supercharger (TGEMS) system. The analysis also allowed for providing evidence of a “backpressure supercompensation effect” associated with rising exhaust backpressure in the ICE. TGEMS introduces a novel compressor group decoupled from the turbine. The analyses were carried out on a 2.0 L turbocharged gasoline direct injection engine. The “supercompensation” phenomenon was isolated using a stepwise procedure in which TGEMS was initially applied to the baseline engine to be exploited on a modified configuration featuring a downscaled turbine. The results were analyzed from the perspectives of specific fuel consumption reduction and total power output as well as operating flexibility increase. The results indicate that, in a context like TGEMS, the assumption that rising exhaust backpressure is always penalizing is no longer valid. Under higher backpressure conditions, TGEMS alone achieved −4.92% in specific fuel consumption at 5000 rpm, with +8.75% in maximum power output. Moreover, with the configuration with a downscaled turbine and the possibility to control the engine operating line, specific fuel consumption reductions of −7.93% at 5000 rpm and −6.83% at 3000 rpm were achieved. The maximum power output increment was +11.04%. These outcomes could open up to new downsizing perspectives and a new generation of “super-backpressured engines”. Full article

Organic Rankine Cycles (ORCs) are widely recognized as an effective solution for waste heat recovery (WHR). However, the design and optimization of these systems must address the tradeoff between computational efficiency and the need to capture complex component behavior. This requires moving beyond purely energetic 0D modeling approaches to account for constructional, spatial, and operational constraints. This work presents a novel modeling framework with a specific focus on the expansion device. Radial inflow turbine stages are selected for their capability to achieve high pressure ratios while maintaining compactness and high efficiency. Heat exchangers follow a generic one-dimensional counterflow configuration, with a shell-and-tube geometry adopted for sizing purposes. The turbine stages are modeled by resolving several internal sections in order to capture local thermofluid dynamic conditions. The framework predicts turbine efficiency and incorporates a newly developed formulation for shock-induced losses, improving performance prediction under trans-sonic flow conditions. After validation against experimental data, the model is applied to a WHR system integrated with an internal combustion engine fueled by biofuels. The results highlight the existence of optimal operating conditions arising from competing physical mechanisms. The analysis also shows the transition from single-stage to two-stage turbine configurations at high pressure ratios and emphasizes the role of real gas effects in determining stage performance and optimal expansion distribution. The results of simulations carried out for three different working fluids (ethanol, toluene, and R1234ze(E)) highlight that the available mechanical power ranges from 10 to 22 kW for single-stage turbine configurations and from 24 to 36 kW for two-stage configurations, with total system volumes varying between approximately 600 and 9000 L. Among the working fluids considered here, ethanol provides the best overall performance for the present case study. Overall, the proposed approach provides a reliable and computationally efficient tool for the preliminary design and optimization of ORC-based WHR systems. Full article

Hydrogen-enriched fuel injection in staged gas-turbine combustors is commonly achieved through jet-in-crossflow (JICF) configurations, where flame stabilization is governed by a local balance between flow-induced strain/mixing and chemical reaction rates. This work investigates turbulent reacting JICF relevant to staged combustion conditions using high-fidelity simulations with adaptive mesh refinement (AMR) and differential-diffusion effects together with Lagrangian particle statistics. Chemistry model uncertainties are incorporated by using a projection method that maps uncertainty estimates from detailed mechanisms into the model used in this work. Results show that the macroscopic flame topology remains in a stable two-branch regime (lee-stabilized and lifted) and is primarily controlled by the jet momentum–flux ratio J. Visualization of the normalized scalar dissipation rate reveals that the flame front resides on the low-dissipation side of intense mixing layers, occupying an intermediate region between over-strained and under-mixed regions. While hydrogen content does not significantly change the global stabilization mode for the cases studied, uncertainty analysis reveals composition-dependent differences that are not apparent in the mean behavior alone. In particular, visualization in Eulerian (χ, T) state-space analysis and particle statistics conditioned on the stoichiometric surface demonstrate that higher-hydrogen cases observe a lower scalar dissipation rate and exhibit substantially reduced variability in OH production under kinetic-parameter perturbations, whereas lower-hydrogen blends experience higher dissipation and amplified chemical sensitivity. These findings highlight that, even in globally similar JICF regimes, the hydrogen content can modify the local response of the flame to kinetic-parameter uncertainty, motivating uncertainty-aware interpretation and design for hydrogen-fueled staging systems. Full article

The continuous drive for higher efficiency in gas turbines has led to increased combustion temperatures, making the thermal shock resistance of thermal insulation tiles a critical factor limiting performance. Corundum–mullite multiphase ceramics are widely used in such applications; however, their performance is often constrained by an inherent trade-off between mechanical strength and thermal shock resistance. In this work, a synergistic modification strategy based on rare-earth disilicate phases was developed, wherein Y₂O₃ and SiC were incorporated into a corundum–mullite matrix to enable in situ formation and controlled distribution of Y₂Si₂O₇ via gel casting. During sintering, Y₂Si₂O₇ acts as a transient liquid phase, facilitating densification and grain boundary strengthening; upon thermal shock, it migrates to fill and heal grain boundaries and microcracks, thereby significantly enhancing thermal shock resistance. The optimized sample S5, sintered at 1400 °C, exhibited a bulk density of 2.12 g/cm³ and a bending strength of 68.43 MPa. Notably, after 30 thermal shock cycles (air cooling from 1000 °C to RT), its bending strength increased to 79.71 MPa, corresponding to a 16.48% enhancement. This work provides an effective strategy for incorporating rare-earth disilicates into multiphase ceramics and offers valuable guidance for the development of high-performance components for gas turbines. Full article