Search Results (34)

This study explores the computational analysis of catalytic combustion in cylindrical reactors using the Finite Volume Method (FVM) within Ansys Fluent. Through the incorporation of a combustion channel to facilitate diesel combustion, Ansys Fluent is utilized to predict the fluid dynamics during catalytic combustion. An extensive reaction mechanism file containing all related reactions is added into Ansys Fluent to model the catalytic combustion of methane. In this study, the catalyzed combustion of a methane, hydrogen, and air mixture is simulated on a heated platinum wall within a cylindrical channel using a 2D axisymmetric solver. Two mechanism files are employed: one defining gaseous species and the other including surface species definitions and surface reactions. Volumetric reactions are excluded from this analysis. The cylindrical channel comprises three sections: inlet, catalytic, and outlet, with the catalyzed reactions occurring on the wall surface of the catalytic section. The simulation results exhibit a gradual decrease in the mass fraction of reactants as catalytic combustion proceeds within the chamber, accompanied by a simultaneous increase in product formation. In particular, the presence of a catalytic channel within the combustion chamber catalyzes the combustion reaction, resulting in a higher chamber temperature. This study also presents predicted mass fraction profiles for both reactants and combustion products, highlighting the efficiency of Computational Fluid Dynamics (CFD) simulations in predicting chemical processes, particularly catalytic combustion. This research contributes to the understanding of complex phenomena such as catalytic combustion and underscores the potential of CFD simulations in explaining complicated chemical processes. Full article

This study develops and validates a three-dimensional CFD model for a 12 L large-bore active-type pre-chamber spark-ignition (PCSI) engine fueled by natural gas. The model incorporates an advanced Extended Coherent Flamelet Model (ECFM-3Z) with a tuned stretch factor to capture complex turbulence–flame interactions, flame propagation, and pollutant formation under ultra-lean conditions. By systematically varying pre-chamber geometries—specifically the orifice diameter, cone angle, diverging tapered nozzle, and volume—the simulations assess their effects on combustion dynamics, heat release rates, turbulent jet penetration, and emissions (NOx and CO). Model predictions of in-cylinder and pre-chamber pressure profiles, combustion phasing, and emission trends are validated against experimental data. The results demonstrate that optimizing pre-chamber and orifice configurations enhances turbulent mixing, accelerates flame development, and reduces local high-temperature zones, thereby suppressing NOx and CO formation. Although some discrepancies in NOx predictions persist due to limitations in current turbulence–chemistry models, the findings offer valuable insights for the design of high-efficiency, low-emission PCSI engines. Full article

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated aluminum alloy melt into the shot sleeve would lead to evaporation and burning of the lubricants once in contact with the piston tip. The burning products, however, would form gas and non-metallic inclusions in the melt which would be transported and injected into the die area and finally trapped in the castings, all of which would affect the mechanical properties of the as-cast samples and deteriorate the product quality. To further investigate this issue, a pilot scale HPDC machine is used and the lubricant burning issue is studied based on material characterization and numerical modelling. The chemical composition, size, and morphology of the burned products are observed using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In order to better explore the issue of lubricant combustion discovered in the experiment, a finite element model describing the entire HPDC process is established and the burning, motion, and trapping of the lubricant are calculated. The final distribution of the burned products such as gas and non-metallic inclusions are predicted and their influence on final solidification quality of the as-cast products under various process parameters are analyzed qualitatively. Finally, a slow shot velocity range of 0.4–0.6 m/s and an acceleration profile that ramps up to 0.3 m/s over 0–370 mm of the shot sleeve proved to be the most effective in reducing air entrainment and oxide inclusions to alleviate the burning of lubricant on final product quality. Full article

The development of modern solid rocket technology with high-performance and high-loading ratio propellants places higher requirements on the safety and stability of the solid rocket motor. The propellant of the solid rocket motor will creep during long-term vertical storage, which may adversely affect its regular operation. The ignition transient process is a critical phase in the operation of solid rocket motors. The Abaqus v.2022 finite element simulation software is used to analyze the ignition transient under propellant creep conditions and obtain the deformed combustion chamber profile. Then, we use a high-precision finite volume solver developed independently to simulate the flow field during the ignition process. In the simulation, we adopt the surface temperature of the propellant column reaching the ignition threshold as the ignition criterion, considering the heat transfer process of the propellant column instead of using the near-wall gas temperature to obtain the set temperature. Simulation results under different creep conditions reveal that the deformation of the propellant grains progressively intensifies as the solid rocket motor’s storage duration increases. This leads to a delayed initial ignition time of the propellant, an advancement of the overall ignition transient process, and an increased pressurization rate during ignition, which can affect the structure and regular operation of the motor. The research results provide design guidance and theoretical support for the design and life prediction of solid rocket motors. Full article

This study investigates the combustion behavior of hydrogen–air mixtures in a closed chamber at reduced initial pressure, focusing on applications in thermal energy methods (TEMs) for plastic processing. The primary goal was to develop and validate a numerical model capable of accurately predicting pressure and temperature profiles over time. By employing ANSYS Fluent 2024 R2 and the GRI-Mech 3.0 mechanism, a detailed combustion model was constructed and validated against experimental data, adhering to the standards outlined in EN 15967: 2011. Subsequent simulations under low-pressure conditions revealed consistent flame front propagation and turbulent flow patterns, crucial factors for achieving stable temperature distributions and optimal part placement. This validated model provides a valuable tool for predicting combustion effects, enhancing safety, and optimizing the performance of hydrogen-fueled TEM processes. By leveraging hydrogen as a clean and sustainable energy source, this research contributes to a more environmentally friendly approach to plastic processing. Future studies will delve into the combustion of hydrogen–air mixtures in the presence of plastic parts to further refine the efficiency and effectiveness of TEM processes. Full article

Reasonably configuring the concentration distribution of the mixture to achieve partially premixed combustion has been proven to be an effective method for improving energy utilization efficiency. However, due to the significant influence of concentration non-uniformity and flow field disturbances, the combustion behavior and mechanisms of partially premixed combustion have not been fully understood or systematically analyzed. In this study, the partially premixed combustion characteristics of methane–hydrogen–air mixtures in a confined space were investigated, focusing on the combustion behavior and key parameter variation patterns under different equivalence ratios (0.5, 0.7, 0.9) and hydrogen contents (10%, 20%, 30%, 40%). The global equivalence ratio and degree of partial premixing of the mixture were controlled by adjusting the fuel injection pulse width and ignition timing, thereby regulating the concentration field and flow field distribution within the combustion chamber. The constant-pressure method was used to calculate the burning velocity. Results show that as the mixture formation time decreases, the degree of partial premixing increases, accelerating the heat release process, increasing burning velocity, and shortening the combustion duration. It exhibits rapid combustion characteristics, particularly during the initial combustion phase, where flame propagation speed and heat release rate increase significantly. The burning velocity demonstrates a distinct single-peak profile, with the peak burning velocity increasing and its occurrence advancing as the degree of partial premixing increases. Additionally, hydrogen’s preferential diffusion effect is enhanced with increasing mixture partial premixing, making the combustion process more efficient and concentrated. This effect is particularly pronounced under low-equivalence-ratio (lean burn) conditions, where the combustion reaction rate improves more significantly, leading to greater combustion stability. The peak of the partially premixed burning velocity occurs almost simultaneously with the peak of the second-order derivative of the combustion pressure. This phenomenon highlights the strong correlation between the combustion reaction rate and the dynamic variations in pressure. Full article

This study investigates the combustion of hydrogen in supercritical gas turbines, emphasizing the optimization of combustor design through computational fluid dynamics (CFD) simulations. Key parameters analysed include the number of oxygen inlets, operating pressure, excess working fluid in oxygen inlets, power output, and the use of different working fluids: supercritical argon (sAr) and supercritical xenon (sXe). The results highlight how these parameters influence temperature distribution, flame stability, and overall combustion efficiency. Findings suggest that increasing the number of oxygen inlets can significantly affect temperature profiles, while higher operating pressures lead to shorter flames. The dilution of oxygen by argon reduces the peak temperatures, and the choice of working fluid impacts cooling efficiency and flame dynamics. This study provides valuable information on optimizing the design of supercritical combustion chambers for hydrogen combustion in novel supercritical gas turbine systems. Full article

Gelled fuels are rheologically complex, non-Newtonian fluids. They combine the benefits of both liquid and solid states, reducing risks of leakage, spilling, and sloshing during storage while maintaining the ability to be sprayed inside a combustion chamber. Additionally, suspending energetic particles, such as metal powders of aluminum and boron, can significantly enhance their energy density compared to conventional liquid fuels. In this study, several kerosene-based and ethanol-based formulations were experimentally investigated, using both organic and inorganic gelling agents. The compositions were optimized in terms of the gellant amount and manufacturing process. Some of the most promising gellants for kerosene include fatty acids, such as Thixcin^® R or THIXATROL^® ST, and metallic soaps, such as aluminum stearate and zinc stearate. The effects of various co-solvents were assessed, including ketones (methyl isoamyl ketone, methyl ethyl ketone, and acetone) and alcohols (ethanol and octadecanol). Sugar polymers like hydroxypropyl cellulose were tested as gelling agents for ethanol. A preliminary rheological analysis was conducted to characterize their behavior at rest and under shear stress. Finally, a novel approach was introduced to study the stability of the gels under vibration, which was derived from a realistic mission profile of a ramjet. Finally, the ideal gravimetric specific impulse was evaluated through ideal thermochemical computations. The results showed that promising formulations can be found in both kerosene-based and ethanol-based gels. Such compositions are of interest in practical airbreathing applications as they have demonstrated excellent stability under vibration, ideal combustion properties, and pronounced shear-thinning behavior. Full article

In the last few decades, the problem of pollution resulting from human activities has pushed research toward zero or net-zero carbon solutions for transportation. The main objective of this paper is to perform a preliminary performance assessment of the use of hydrogen in conventional turbine engines for aeronautical applications. A 0-D dynamic model of the Allison 250 C-18 turboshaft engine was designed and validated using conventional aviation fuel (kerosene Jet A-1). A dedicated, experimental campaign covering the whole engine operating range was conducted to obtain the thermodynamic data for the main engine components: the compressor, lateral ducts, combustion chamber, high- and low-pressure turbines, and exhaust nozzle. A theoretical chemical combustion model based on the NASA-CEA database was used to account for the energy conversion process in the combustor and to obtain quantitative feedback from the model in terms of fuel consumption. Once the engine and the turbomachinery of the engine were characterized, the work focused on designing a 0-D dynamic engine model based on the engine’s characteristics and the experimental data using the MATLAB/Simulink environment, which is capable of replicating the real engine behavior. Then, the 0-D dynamic model was validated by the acquired data and used to predict the engine’s performance with a different throttle profile (close to realistic request profiles during flight). Finally, the 0-D dynamic engine model was used to predict the performance of the engine using hydrogen as the input of the theoretical combustion model. The outputs of simulations running conventional kerosene Jet A-1 and hydrogen using different throttle profiles were compared, showing up to a 64% reduction in fuel mass flow rate and a 3% increase in thermal efficiency using hydrogen in flight-like conditions. The results confirm the potential of hydrogen as a suitable alternative fuel for small turbine engines and aircraft. Full article

The development of modern reusable launchers, such as the Themis project with its LOX/LCH4 Prometheus engine, CALLISTO—a reusable VTVL-launcher first-stage demonstrator with a LOX/LH2 RSR2 engine, and SpaceX’s Falcon 9 with its Merlin 1D engine, underscores the need for advanced control algorithms to ensure reliable engine operation. The multi-restart capability of these engines imposes additional requirements for throttling, necessitating an extended controller-validity domain to safely achieve low thrust levels across various operating regimes. This capability also increases the risk of component failure, especially as engine parameters evolve with mission profiles. To address this, our study evaluates the dynamic reliability of reusable rocket engines (RREs) and their subcomponents under different failure modes using multi-physics system-level modelling and simulation, with a particular focus on turbopump components. Transient condition modelling and performance analysis, conducted using EcosimPro-ESPSS software (version 6.4.34), revealed that turbopump components maintain high reliability under nominal conditions, with turbine blades demonstrating significant fatigue life even under varying thermal and mechanical loads. Additionally, the proposed predictive model estimates the remaining useful life of critical components, offering valuable insights for improving the longevity and reliability of turbopumps in reusable rocket engines. This study employs deterministic, thermally dependent structural simulations, with key control objectives including end-state tracking of combustion chamber pressure and mixture ratios and the verification of operational constraints, exemplified by the LUMEN demonstrator engine and the LE-5B-2 engine class. Full article

The current investigation aims to develop a validated numerical model of a confined, swirl-stabilized diffusion flame. This model will assist in designing and optimizing novel combustion chambers while reducing computational costs. To achieve this objective, experimental and numerical studies were conducted on NH₃/natural gas combustion using a laboratory-scale burner capable of operating under fuel-flexible conditions. The burner fired 5 kW flames of blended ammonia with natural gas in concentrations up to 100% NH₃. The burner’s performance for relevant industrial applications was assessed through measurements of axial temperature profiles, exhaust temperature, and gas emissions. Numerical simulations were conducted by employing the commercial CFD software STAR-CCM+ 2020.2.1. Numerical simulations for steady-state were performed using a realizable k-$ϵ$ turbulence model coupled with the EDC (eddy dissipation concept) for combustion. The investigation utilized a 3D periodic domain for the simulations and investigated mesh independence and the influence of the flame dynamics. The burner was able to operate with different fuel mixtures while maintaining stabilized flames under every condition. However, the appearance of increased ammonia slip was observed for 100% NH₃ up to 1250 ppm (dry vol.). The present work demonstrates and assesses the readiness and potential of fuel-flexible burners as cost-effective and efficient transitional technologies for integrating ammonia and other sustainable fuels into combustion applications. Full article

This manuscript presents an experimental study focusing on the combustion of magnesium in an atmosphere depleted of oxygen. The study explores various mixtures of carbon dioxide and nitrogen, examining their impact on the combustion performance. The experimental design involved evaluating how the carbon content influences combustion parameters. Temperature profiles were analyzed to elucidate different stages of the combustion process. Furthermore, the effects of pressure (2 and 3 ata) and the composition of CO₂-N₂ mixtures (10%, 19.5%, 35%, 48%, 72%, and 80% CO₂ content) on magnesium combustion, including ignition time, maximum temperature, and post-combustion temperatures, were investigated. The results revealed a substantial impact on the ignition delay and combustion time, with the ignition delay decreasing with higher chamber pressure. The combustion process, especially with regard to the ignition time and heat of combustion, was notably affected by CO₂ concentration. The morphology of the combustion residue from the magnesium microparticles was characterized using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The reaction of Mg with CO₂ represents a promising energy source, quickly releasing a substantial amount of heat with a very low quantity of Mg. The estimated value of the heat of combustion for magnesium in N₂-CO₂ atmosphere is 78.4 kJ mol⁻¹. Full article

In diesel engines, emission formation inside the combustion chamber is a complex phenomenon. The combustion events inside the chamber occur in microseconds, affecting the overall engine performance and emissions characteristics. This study opted for using computational fluid dynamics (CFD) to investigate the combustion patterns and how these events affect nitrogen oxide (NO_x) emissions. In this study, a diesel engine model with a flat combustion chamber (FCC) was developed for the simulation. The simulation result of the heat release rate (HRR) and cylinder pressure was validated with the experimental test data (the engine test was conducted at 1500 rpm at full load conditions). The validated model and its respective boundary conditions were used to investigate the effect of modified combustion chamber profiles on NO_x emissions. Modified chambers, such as a bathtub combustion chamber (BTCC) and a shallow depth chamber (SCC), were developed, and their combustion events were analysed with respect to the FCC. This study revealed that combustion events such as fuel distribution, unburnt mass fractions, temperature and turbulent zones directly impact NO_x emissions. The modified chambers controlled the spread of combustion and provided better fuel distribution, improving engine performance and combustion rates. The SCC (63.2 bar) showed peak pressure rates compared to the FCC (63.02 bar) and BTCC (62.72 bar). This study concluded that the SCC showed better results than other chambers. This study further recommends conducting lean fuel mixture combustion with chamber modifications and optimising fuel spray, such as by adjusting the fuel injection profile, spray angle and injection timing, which has a better tendency to create complete combustion. Full article

Due to the extreme temperatures inside the combustion chambers of liquid propellant rocket engines, the walls of the combustion chamber and the nozzle are cooled by either the fuel or the oxidizer in what is known as regenerative cooling. This study presents an indigenous computational tool developed for the analysis of heat transfer in regenerative cooling of such rocket engines. The developed tool incorporates a one-dimensional (1-D) combustion analysis to calculate the thermophysical properties of the combustion gas. Basic engine properties were calculated and used to generate a thrust chamber profile based on a bell-shaped nozzle. The hot gas side was analyzed using 1-D isentropic flow assumptions, along with heat transfer correlations. The coolant side was evaluated using the hydraulic analysis in the axial direction and the heat transfer analysis in the radial direction. Thermophysical properties and the phase of the coolant were determined using the given property tables and the instantaneous state of the coolant. This flexible and computationally less demanding tool was used to analyze two small-scale engines utilizing liquid hydrocarbon fuels, which are used in modern rocket propulsion. The wall cooling analyses of a liquid oxygen (LOX)/liquid methane (LCH₄) engine and a liquid oxygen (LOX)/liquid propane (LC₃H₈) engine are presented. Fuel and oxidizer were used separately as coolants for both engines, and both of them experienced phase change. Results reveal the advantage of the high mass flow rate of the oxidizer in cooling performance. In addition, the results of this study show that the cooling of the LOX/LC₃H₈ engine is somewhat more challenging compared to the LOX/LCH₄ engine. Full article

Computational fluid dynamics techniques were applied to reproduce the characteristics of the liquid methanol burner described in a previous paper by Guevara et al. In this work, the unstable Reynolds-averaged Navier–Stokes (U-RANS) approach known as the Scale-Adaptive Simulation (SAS) model was employed, together with the steady nonadiabatic flamelets combustion model, to characterize and compare methanol and hydrogen flames. These flames were compared to determine whether this model can reproduce the coherent dynamic structures previously obtained using the LES model in other investigations. The LES turbulence model still entails a very high computational cost for many research centers. Conversely, the SAS model allows for local activation and amplification, promoting the transitions of momentum equations from the stationary to the transient mode and leading to a dramatic reduction in computational time. It was found that the global temperature contour of the hydrogen flame was higher than that of methanol. The air velocity profile peaks in the methanol flame were higher than those in hydrogen due to the coherent structures formed in the near field of atomization. Both flames presented coherent structures in the form of PVC; however, in the case of hydrogen, a ring-type vortex surrounding the flame was also developed. The axial, tangential, and radial velocity profiles of the coherent structures along the axial axis of the combustion chamber were analyzed at a criterion of Q = 0.003. The investigation revealed that the radial and tangential components had similar behaviors, while the axial velocity components differed. Finally, it was found that, using the SAS model, the coherent dynamic structures of the methanol flame were different from those obtained in previous works using the LES model. Full article