Search Results (62)

This study compares the standart (STD) piston with a specially designed MR-1 piston that better meets modern requirements. Firstly, the experimental comparison was conducted at 3000 rpm, with static fuel injection timing advance (ITA) of (30°, 25°, 20°, 17.5°) CA BTDC, and engine load conditions of 100%, 75%, 50%, 25%. Subsequently, the combustion chambers (CCs) were simulated at the same ITA to examine in-cylinder phenomena in more detail. Analysis was performed at full load, where emissions are critical. Reducing the ITA to decrease combustion temperature and NOx emissions resulted in higher soot and UHC emissions, particularly for the STD chamber. However, this trend was not observed with the MR-1 chamber. NOx was reduced further thanks to the lower local peak temperatures, and there was no increase in soot without a significant loss in performance. The increase in UHC was negligible compared to the STD, while CO decreased. The advantages of the MR-1 can be attributed to its ability to increase air movement in the vertical direction, which is better suited for the bowl geometry and spray direction. This results in improved mixture formation in the cylinder by increasing turbulent kinetic energy (TKE) to an optimal level. Additionally, the temperature distribution is more uniform when considering dimensions, heat release duration is shortened and lower pressure and pressure rise rate are achieved. Full article

Optimizing fuel injector geometry represents a critical pathway toward cleaner and more efficient diesel combustion. This study presents a comprehensive numerical investigation of the influence of the dual-hole nozzle injection angle on the primary atomization behavior and spray hydrodynamics of high-pressure diesel jets. The present analysis is deliberately restricted to cold-flow, near-nozzle primary breakup under isothermal conditions (293.15 K) so that the hydrodynamic and aerodynamic breakup mechanisms can be isolated in the immediate vicinity of the orifice before evaporation and combustion occur. Two-dimensional simulations are conducted using an Eulerian Volume-of-Fluid (VOF) framework with finite element discretization, three injection-angle configurations (0°, 5°, and 10°) under realistic engine conditions (injection pressure: 138 MPa; chamber pressure: 2.32 MPa; nozzle diameter: 100 µm). The numerical model was validated against the experimental and computational benchmark data of Ménard et al., showing reasonable qualitative agreement in jet morphology, although the 2D nature of the model leads to an exaggerated accumulation of liquid at the spray tip compared to the 3D reference. The validation therefore supports the qualitative trends and the relative angular comparison, but the absolute quantitative predictions remain subject to this 2D structural limitation. Results reveal that the injection angle exerts a decisive influence on the competition between axial momentum and radial dispersion. The neutral 0° configuration yields an overly concentrated jet with limited interfacial destabilization and poor air entrainment, whereas the 10° angle produces excessive radial spreading at the expense of axial penetration depth. By contrast, the 5° convergence angle provides the best trade-off among the three tested configurations under the studied conditions, promoting enhanced Rayleigh–Plateau instability growth, earlier ligament formation, and finer droplet generation—favorable to a more homogeneous air–fuel mixture. These findings provide quantitative guidance for dual-hole injector geometry design and demonstrate the suitability of high-fidelity VOF-based methods for resolving complex two-phase atomization phenomena relevant to low-emission diesel engine design. Quantitatively, the peak axial velocity is reached at the nozzle exit for all configurations; relative to the 0° baseline, the 5° convergence angle increases the fuel–air interfacial spreading by about 141% while retaining roughly 90% of its axial penetration at the monitoring positions P₁–P₃, whereas the 10° case loses about 26% of axial penetration for a comparable radial spread. Full article

Computational fluid dynamics provides detailed spatial distributions of physical fields in biomass boiler combustion, but the computational cost of each simulation limits its application in parametric studies and near-real-time workflows. This work investigates whether a Graph Neural Operator (GNO) can serve as a fast surrogate model that maps boiler operating parameters to six coupled CFD field distributions simultaneously. The reference case is a 10 kW wood-pellet boiler with internal flue gas recirculation (FGR), described and experimentally validated in an earlier publication by the authors. CFD data were collected on the symmetry plane of the combustion chamber for 80 operating points defined by the thermal load ratio (P/P₀) and the excess air ratio λ. A GNO surrogate was trained on 64 cases to predict temperature, velocity magnitude, static pressure, and mole fractions of CO, O₂, and CO₂ at each node of an unstructured spatial graph. On a held-out validation set of 16 operating cases, the model achieved R² values of 0.988 for temperature, 0.919 for velocity magnitude, 0.982 for pressure, 0.999 for CO, 0.992 for O₂, and 0.985 for CO₂. After training, each prediction is generated in a single forward pass, providing a computationally efficient approximation compared to the full CFD solver. A dedicated generalisation study on independent off-grid CFD cases confirmed that the surrogate interpolates within the parameter domain with essentially no loss of accuracy and degrades only moderately when extrapolated towards a higher thermal load and leaner mixtures. The results demonstrate that a baseline GNO surrogate can capture the spatial structure of coupled thermo-fluid and species fields in a realistic combustion geometry within the investigated parameter range and suggest applicability to digital-twin-oriented workflows where repeated parametric queries of boiler operation are required. Full article

Rotating detonation engines combine compact geometry with the potential for higher specific impulse compared to deflagration-based propulsion, enabled by pressure-gain combustion. However, their increased thermal loads present a major challenge. In the current literature, thermal characterisation of rotating detonation hardware relies either on experimental reconstructions or on high-fidelity simulations. A predictive and coolant-coupled low-order heat transfer model for rotating detonation rocket engines is not yet available in the open literature. This paper introduces such a reduced-order predictive tool for rotating detonation combustors, capable of estimating both cycle-averaged wall heat flux and coolant thermal behaviour. Implemented in Python, the tool supports any propellant available in NASA’s Chemical Equilibrium with Applications and CoolProp, handles single-phase thermodynamic regimes, and spans geometric and operating ranges from laboratory-scale test rigs to engine-relevant conditions. With computation times below one second, it enables rapid trade studies, model-based screening, and sensitivity analyses. Benchmarking was performed against experimental test cases covering ${\mathrm{H}}_2/{\mathrm{O}}_2$, ${\mathrm{CH}}_4/{\mathrm{O}}_2$ and ${\mathrm{C}}_2{\mathrm{H}}_4/{\mathrm{O}}_2$ mixtures, as well as multiple injector geometries and chamber configurations. The approach complements existing high-fidelity tools by offering a low-order alternative grounded in transparent assumptions and benchmarked against multiple datasets. Full article

Graphite nozzles remain the dominant choice for small hybrid and solid rocket motors operating on laboratory and university budgets, owing to their low cost, ease of machining, and rapid turnaround during iterative design campaigns. These same programs, however, must contend with the fact that graphite erodes through coupled thermochemical and mechanical mechanisms when exposed to the oxidizing species generated by high-energy propellant combustion, and the resulting throat-area growth fundamentally alters the time histories of chamber pressure, thrust, and delivered specific impulse. This paper presents a nozzle-erosion reconstruction model that extracts the time-resolved throat area from coupled thrust and chamber-pressure measurements using the thrust coefficient relationship, scales the reconstructed area history against pre- and post-test throat measurements, identifies the onset and rate of erosion, and accounts for variable sensor lag between the thrust-stand and pressure-transducer signal chains. The model is exercised on two complementary sets of laboratory-scale GOX/ABS hybrid hot-fire data that together span roughly two orders of magnitude in total throat-area change and peak chamber pressures from 0.5 to 3.4 MPa: a controlled three-operating-point campaign conducted in support of the NASA Plume-Surface Interaction (PSI) program, and a set of higher-pressure firings from the laboratory development series in which the technique was matured. Reconstructed erosion-onset times, erosion rates, and total throat-diameter change are reported for each firing, the reconstruction accuracy is characterized as a function of erosion magnitude. A correlation of graphite erosion with chamber pressure is examined across the combined envelope. The results demonstrate the robustness of the reconstruction technique and provide a reusable framework for post-test reconstruction of transient nozzle geometry in rocket-engine ground testing. Full article

To address the high experimental costs and data scarcity inherent in Directed Energy Deposition (DED), this study proposes a data-efficient hybrid optimization framework for the precision manufacturing of Inconel 718 aerospace components. The framework leverages a two-stage strategy to bridge traditional experimental design with advanced machine learning, ensuring robust process optimization even with limited datasets. In the first stage, the Taguchi method (L16 orthogonal array) was employed for coarse-grained screening to identify influential control factors. In the second stage, a Fully Connected Neural Network (FNN) coupled with Bayesian Optimization (BO) was deployed. Crucially, this machine learning component functions as an optimization-oriented trend surrogate rather than a global regressor, successfully guiding the optimization under extreme data scarcity. The optimized process window yielded exceptional structural integrity, achieving a porosity as low as 0.03%. To thoroughly validate its practical efficacy, tensile testing (ASTM E8/E8M) and Rockwell hardness measurements (ASTM E18) were systematically conducted on the optimized specimens. The mechanical characterization demonstrated an average tensile strength of approximately 1358 MPa and a hardness of ~40 HRC. Finally, the framework was successfully validated through the robotic DED fabrication of a complex-geometry aerospace engine combustion chamber casing, bridging laboratory-scale optimization with authentic industrial applications. Full article

This study explores key technological challenges and innovative strategies for improving the combustion performance and emission characteristics of low-carbon fuel engines, with a focus on natural gas applications. The core bottlenecks of natural gas combustion, including slow combustion speed and high methane slip under lean burn conditions due to wall quenching, crevice effects, and the long distance of flame propagation from the ignition zone to the whole cylinder, are analyzed. The decarbonization of engines further aggravates these issues. Technological solutions are summarized in four categories, including turbulence enhancement, high-energy ignition, fuel reactivity modification, and fuel synergy with zero-carbon fuels. Geometry modifications of the combustion chamber, dual-fuel operation, pre-chamber ignition, and fuel activation are systematically reviewed and evaluated. A fusion technology integrating diesel pilot ignition with jet flame propagation is analyzed as a new combustion concept, termed induced jet flame combustion. This approach demonstrates significant potential in enhancing both combustion efficiency and stability, especially for lean burn conditions. This work highlights the role of natural gas engines as a transitional technology and a support platform for ultralow-emission and high-efficiency power systems fueled with low/zero-carbon fuels in the context of global decarbonization goals. Full article

Solid fuel ramjets (SFRJs) are air-breathing propulsion systems with a high specific impulse, but their sudden expansion combustors often exhibit axially nonuniform fuel regression because of the distinct recirculation, reattachment, and downstream turbulent diffusion flame regions. However, previous studies have primarily focused on the average regression rate, with limited attention to local combustion characteristics. This study applied a photogrammetry-based three-dimensional shape reconstruction technique to obtain the post-combustion internal port geometry of a sudden-expansion SFRJ combustor burning high-density polyethylene fuel under different chamber pressure and air mass flux conditions. This geometry was employed to determine the axial distributions of the local regression rates. The analysis procedure was validated against the corresponding space–time averaged regression rate obtained from fuel mass loss, showing suitable agreement with relative errors of 1.7–5.7%. The axial distributions consistently exhibited low values in the upstream, increased rapidly in the middle region, and sustained high or gradually decreasing in the downstream. In addition, an empirical expression for the space–time averaged regression rate indicated greater sensitivity to air mass flux than chamber pressure. These results confirm that photogrammetry is an effective tool for resolving the axially nonuniform regression behavior and informing spatial insights beyond the average regression rate alone. 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

Hybrid rocket engines offer a compromise between safety, controllability, and performance, making them attractive for small-scale propulsion systems. However, oxidizer selection remains a critical early-stage design decision that cannot be determined solely from ideal thermodynamic metrics. This study presents a comparative analysis of three oxidizers—nitrous oxide (N₂O), gaseous oxygen (GOX), and liquid oxygen (LOX)—for a 1 kN-class hybrid rocket engine using HDPE fuel under identical operating conditions. Equilibrium combustion performance was first evaluated using NASA Chemical Equilibrium with Applications (CEA) to determine optimal oxidizer-to-fuel ratios and theoretical specific impulse. These results were subsequently refined using Rocket Propulsion Analysis (RPA) to incorporate finite combustion chamber geometry and non-ideal nozzle expansion effects. The equilibrium analysis predicts maximum specific impulses of approximately 260 s for N₂O/HDPE and nearly 300 s for oxygen-based systems. However, finite-geometry modelling indicates that practical performance is reduced by approximately 5–8%, yielding delivered specific impulses of about 275 s for GOX and 272 s for LOX. The results demonstrate that although oxygen (GOX and LOX) provides higher thermodynamic performance, the practical advantage of LOX over GOX becomes marginal at the kilonewton scale. Consequently, oxidizer selection for small hybrid engines should be treated as a system-level trade-off involving performance, infrastructure complexity, and operational safety. Full article

Aviation heavy-fuel piston engines are widely used in UAVs, general aviation, and military platforms due to their fuel efficiency and adaptability. However, emissions of NO_x, PM, and other pollutants pose significant environmental challenges. This paper reviews emission-reduction strategies, including combustion-chamber optimization, fuel-injection control, alternative fuels, and exhaust after-treatment technologies. Research indicates that optimizing combustion-chamber geometry, high-pressure common-rail injection, and turbulence enhancement improve combustion efficiency and reduce emissions. Biofuels, synthetic aviation fuels (SAF), and hydrogen-based fuels demonstrate strong potential for low-carbon emissions, while after-treatment technologies such as SCR, DPF, and EGR effectively mitigate NO_x and PM emissions. Despite technological advancements, challenges remain in balancing combustion efficiency with NO_x control and ensuring compatibility between EGR and combustion stability. Future advancements in intelligent combustion control, novel catalytic materials, low-temperature combustion, and high-efficiency after-treatment systems will drive aviation diesel engines toward lower emissions, higher efficiency, and greater intelligence, contributing to the green and sustainable transformation of aviation propulsion systems. Full article

Artillery shells are usually large-caliber projectiles fired by artillery guns. Present long-range artillery shells use techniques such as the base bleed system to reduce the drag coefficient of the shell, but could only increase the range of the shell by around 20–30%. This paper explores the feasibility of designing a ramjet-propelled artillery shell without altering the gun in its existing form. In this theoretical study, a ramjet propulsion system was attached to a 122 mm artillery shell to constitute a 155 mm artillery shell, an industry standard widely used by armies worldwide. The muzzle velocity of the shell provides sufficient velocity for the efficient operation of the ramjet engine. A front air intake portion is designed for the supersonic flow to ingest a high mass flow rate to the engine’s combustion chamber. Characteristics such as net thrust developed by the engine, combustion efficiency, and its changes to geometry modifications are discussed in this study. Full article

In this paper, experimental and numerical analyses are performed with a Rapid Compression and Expansion Machine (RCEM) equipped with a passive pre-chamber (PC) and fueled with premixed stoichiometric air/methane mixture to replicate engine-like conditions. The main objective of this work is to study the effects of PC geometry, initial charge conditions and hydrogen addition to methane on combustion and flame extinction. From the experiments at different PC geometries, the combustion images acquired with a high-speed camera show the existence of a critical PC configuration (Long φ4) exhibiting the highest flame extinction probability (~54% under baseline conditions). The increase in the initial charge pressure and/or the enrichment of the methane with hydrogen (up to 30% H₂ by volume) help to mitigate the flame extinction by reducing its probability to about 10%. Subsequently, a 0D RCEM model is developed (GT-Power^TM) and enhanced with user sub-models of turbulent combustion and flame quenching. Once tuned, the model reproduces the impact of PC design, higher initial gas pressure and hydrogen enrichment on the combustion evolution. The quenching sub-model, calibrated for the side wall quenching configuration, is able to forecast the experimental flame extinction tendency for the critical PC by modifying the hydrogen enrichment or initial gas pressure. The proposed methodology, describing the flame extinction tendency in PC combustion systems through 0D quenching modeling, represents the novel aspect for PC-equipped devices aiming to support their study and supplement engine investigations during the development phase. Full article

This study used a Systemic Modeling technique, based on the methodologies of Churchman and Ackoff, to integrate and assess the subsystems regulating the functionality of a Rocket Candy (R-Candy) motor. The nozzle and combustion chamber design was improved using a five-phase systemic architecture to assure the coherent interplay of essential factors, including pressure, temperature, and velocity fields. The principles of experimental rocketry are elucidated through the examination of impulse performance throughout class A to class C engines. A preliminary design was developed in SolidWorks 2024, incorporating the engine’s three main components: the igniter, the combustion chamber, and a convergent–divergent nozzle that enhances the acceleration of the exhaust gases. The system model was validated using simulations in FEATool and verified through experimentation. This allowed for the analysis of fluid behavior, as well as the geometry of the structures, initial parameters, and boundary conditions. The results demonstrate a strong correlation between the simulations and the experimental data, with discrepancies of less than 1.5%, confirming the reliability and feasibility of the nozzle design. The findings indicate that systemic modeling, in conjunction with CFD and experimentation, can provide a strategic framework for iterative refinement, optimization of key performance metrics, and the development of cost-effective, high-performance R-Candy engines for educational and experimental purposes. Full article

Elastomeric ablative coatings are essential for protecting solid rocket motor (SRM) combustion chambers from extreme thermal and erosive environments, and their performance is governed by both material composition and processing strategy. This review examines the main elastomer systems used for SRM insulation, including ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), hydroxyl-terminated polybutadiene (HTPB), polyurethane (PU), silicone-based compounds, and related hybrids, and discusses how their rheological behavior, cure kinetics, thermal stability, and ablation mechanisms affect manufacturability and in-service performance. A comprehensive assessment of coating technologies is presented, covering casting, molding, centrifugal forming, spraying, automated deposition, and emerging additive-manufacturing approaches for complex geometries. Emphasis is placed on processing parameters that control adhesion to metallic substrates, layer uniformity, defect formation, and thermomechanical integrity under high-heat-flux exposure. The review integrates current knowledge on how material choice, surface preparation, and application sequence collectively determine insulation efficiency under operational SRM conditions. Practical aspects such as scalability, compatibility with complex chamber architectures, and integration with quality-control tools are highlighted. By comparing the capabilities and limitations of different materials and technologies, the study identifies key development trends and outlines remaining challenges for improving the durability, structural robustness, and ablation resistance of next-generation elastomeric coatings for SRMs. Full article