Hypergolic ignition systems have traditionally relied on toxic propellants such as MMH/NTO, prompting a global shift toward greener alternatives. High-Test Peroxide (HTP), with its high oxygen content and clean decomposition products, has emerged as a promising oxidizer when paired with kerosene and suitable catalysts. However, a mechanistic understanding of HTP–fuel ignition, especially with metal-organic catalysts under varying conditions, remains underdeveloped. Here, a comprehensive experimental and kinetic study of hypergolic ignition using Mn (II) acetylacetonate-doped kerosene with HTP is presented across a wide parametric space (HTP: 85–98 %; catalyst: 0.5–10 wt%; O/F: 4.5–7.5; T: 20–50 °C). The results reveal that ignition delay times (IDTs) reduce by over 30 % with preheating and optimal catalyst loading, and deconvoluted phase-wise IDTs show that Mn(II)AA primarily accelerates HTP decomposition and chemical ignition. Derived apparent activation energies (E_a ≈ 10.0 kJ/mol) are consistently low, while the Arrhenius pre-exponential factor (A) increases significantly with catalyst and oxidizer concentration, indicating catalytic efficiency and diminishing returns beyond 5 wt%. Peak flame temperatures exceeding 1200 °C confirm robust energy release, with high-speed imaging further revealing a transition to rapid, spatially distributed ignition under optimal conditions. These findings offer quantitative mechanistic insights into catalyst-enhanced HTP ignition and establish a framework for optimizing green bipropellant systems for aerospace propulsion.

Zirconium diboride (ZrB₂)–silicon carbide (SiC) composites are promising candidates for ultra-high temperature applications, yet optimizing their densification and mechanical performance without sintering additives remains a challenge. This study systematically investigates the independent and combined effects of three critical spark plasma sintering (SPS) parameters, that is, temperature, applied pressure, and dwell time, on the densification behavior, microstructure, and mechanical properties of ZrB₂–20 vol% SiC composites. Building upon prior work on powder preparation effects (e.g., Tungsten Carbide (WC) vs. ZrO₂ milling), this research uniquely focuses on how precise control of sintering conditions alone can tailor final material characteristics. The results demonstrate that optimizing sintering parameters yields significant property enhancement, achieving a maximum relative density of 99.2% (at 2100°C, 65 MPa, 15 min) and peak flexural strength of 516 MPa (at 2000°C, 65 MPa, 60 min). Hardness and fracture toughness reached 17.08 GPa and 3.85 MPa m^1/2, respectively, under optimized conditions. Through detailed microstructural and performance analysis, this work explains the fundamental role of individual sintering parameters in governing densification kinetics and mechanical outcomes. The findings offer practical guidance for additive-free, energy-efficient processing of ZrB₂–SiC ceramics for advanced aerospace and thermal protection systems.

The transition towards non-toxic, high-performance spacecraft propulsion has positioned highly concentrated hydrogen peroxide (HTP) and kerosene as a leading green propellant combination. However, achieving reliable hypergolic ignition in non-polar hydrocarbons remains a critical challenge due to significant physical mixing limitations and high chemical activation barriers. This study investigates the catalytic efficacy of Manganese(III) acetylacetonate (Mn(III)AA) dissolved in aviation-grade kerosene to enable rapid hypergolicity with 98% HTP. High-speed imaging and thermal diagnostics were employed to map the ignition delay time (IDT) across a range of catalyst loadings (0.5–10 wt%) and oxidizer-to-fuel ratios (4.5–7.5). The results demonstrate that Mn(III)AA is highly effective, achieving a minimum IDT of 25 ms at 50°C. Kinetic analysis revealed a significant reduction in apparent activation energy (9 to 14 kJ/mol), accelerating the chemical reaction rate until the system becomes limited by physical mixing processes. Notably, a non-linear performance trend was observed, where catalyst additions beyond 5 wt% yielded diminishing returns, suggesting a saturation threshold for practical engine design. These findings establish Mn(III)AA as a viable, high-efficiency additive for green bipropellant systems.

The urgent need for sustainable propulsion solutions has accelerated the exploration of green bipropellant thrusters using high-test hydrogen peroxide (HTP) with kerosene. In this study, a transient, high-fidelity CFD model coupling droplet-phase dynamics, real-gas behavior, and finite-rate chemical kinetics was developed to simulate the ignition and combustion processes in a coaxial-injected HTP-kerosene thruster. Simulations investigated the impact of oxidizer purity (95 % and 98 %) and mixture ratio variations, targeting a vacuum thrust of 100 N. Results revealed that stoichiometric mixtures with 98 % HTP delivered the most favorable balance of thrust (63.22 N at sea level) and thermal loads, with combustion temperatures aligning within 1 % of CEA predictions. Fuel-rich mixtures exhibited significant inefficiencies, with up to 18 % unburnt kerosene detected at the nozzle exit. Wall temperatures peaked at 3271 K under adiabatic assumptions, exceeding material safety thresholds, highlighting the necessity of advanced thermal management strategies. Observations of flow separation, shock structures, and model-predicted oxygen backflow further reinforced the realism of the simulations. This study advances green propulsion by linking combustion dynamics with structural viability. It provides new insights into propellant formulation, thermal management, and injector optimization for future environmentally compliant engines.

To address concerns regarding toxicity inherent in conventional storable brpropellants, the propulsion community is actively exploring "green" alternatives. Hydrogen peroxide (HTP), paired with eco-fnendly fuels such as kerosene or ethyl alcohol, is emerging as a promising option due to its potential for cost reduction in space launch, enhanced safety, ease of handling, and favorable density-impulse characteristics. This study investigates the hypergohcity and combustion dynamics of HTP with kerosene doped with organic manganese-based additives, targeting application in a 100 N class upper-stage thruster. The experimental campaign employs 95% and 98% HTP combined with variable catalyst loadings in kerosene to optimize ignition behavior and combustion performance. Drop tests were performed under controlled conditions to characterize ignition delay times (IDT) and post-ignition flame temperatures, supported by high-speed imaging and infrared diagnostics. Two O/F ratios (6.5 and 7.5) were explored to balance stoichiometric efficiency and ignition responsiveness. Comparative evaluation of Mn(II)AA and Mn(III)AA catalysts was conducted across a unified experimental matrix, with Mn(III)AA consistently outperforming Mn(II)AA by enabling faster ignition and higher combustion efficiency. Furthermore, the demonstration of catalytic hypergohcity eliminates the need for a conventional HTP decomposition catalyst bed, simplifying propulsion system architecture and reducing engine mass and cost. These findings provide critical data for the development of next-generation green propulsion systems, contributing to lighter, simpler, and safer thrusters for space applications. This research is an integral part of the EU Horizon Mane Sklodowska-Cune Actions (MSCA) funded initiative GREENLAM project, which aligns with the overarching goals of the EU Horizon initiative, facilitating technological innovation and advancements in the aerospace industry for the benefit of space exploration and satellite deployment.

This study investigates the impact of different powder milling methods on the densification and mechanical properties of ZrB₂-SiC ceramic composites processed via spark plasma sintering (SPS). Powders were prepared using two ball milling techniques: tungsten carbide (WC) and conventional ZrO₂. The densification behavior during SPS was monitored, and the sintered samples were evaluated for their relative density, hardness, fracture toughness, and flexural strength. Results show that WC milling significantly enhances densification, achieving 99.2 % relative density at 2100 °C/65 MPa/15 min, compared to 96.5 % for ZrO₂-milled samples. This improvement is due to WC's sintering aid effect, which promotes grain boundary diffusion and particle packing. However, ZrO₂-milled composites exhibit superior hardness (17.38 GPa) and fracture toughness (3.97 MPa m¹/²), attributed to their refined grain structure and the absence of softer ZrO₂ phases. Conversely, WC-milled samples show slightly higher flexural strength (384–516 MPa), likely due to the transformation toughening effect of the secondary ZrO₂ phase. Overall, WC milling improves densification and flexural strength, while ZrO₂ milling yields finer-grained composites with higher hardness and toughness, making it better suited for wear-resistant and mechanically demanding applications.

This work examines the vibration, damping, and instability properties of cylindrical shells comprised of glass fiber-reinforced polymer (GFRP) composite reinforced with carbon nanotubes (CNT). The 2 wt.% CNT-reinforced composites are created using the vacuum-assisted hand layup method. An experimental investigation was done to examine the material characteristics of CNT-reinforced GFRP composites. The results indicate that the CNT reinforced composite exhibits superior material characteristics. A finite element method-based higher-order shear deformation theory (HSDT) is used to obtain the governing equations for the cylindrical shell. Further, a thorough parametric study is conducted to examine the effect CNT reinforcement, curvature ratio, thickness ratio and aspect ratio on the vibration, damping, and instability characteristics of the cylindrical GFRP shell. From the obtained results, it can be concluded that the 2 wt.% CNT reinforcement greatly influences the vibration, damping, and instability characteristics of the cylindrical shells.

Hydrazinium nitroformate (HNF) is a chlorine-free, high-energy oxidizer with promising applications in green propulsion systems. This review examines the thermal decomposition, combustion kinetics, flame structure, and behavior of HNF, while critically evaluating the current body of literature. Thermal studies reveal that HNF undergoes two-stage decomposition, with exothermic peaks at 136°C and 138°C and an activation energy of 150 kJ/mol, determined using Kissinger and Ozawa methods. The decomposition products include nitroform, hydrazine, and nitrogen oxides, with a 72.5% weight loss in the first stage (105°C–142°C) and 24.5% in the second stage (142°C–210°C). Combustion studies identify a three-zone flame structure: fizz zone, dark zone, and luminous flame zone, with temperatures ranging from 1320 to 1540 K near the surface to 2720 K in the outer flame. HNF exhibits a high-pressure exponent (∼0.85), necessitating optimization through burn rate modifiers (BRMs) and advanced formulations. While HNF demonstrates superior specific impulse and reduced exhaust plume radiation compared to ammonium perchlorate (AP), its needle-like crystal morphology poses challenges for handling and propellant integration. This review emphasizes the need for advanced diagnostic techniques, computational modeling, and innovative BRMs, along with polymeric binders that are compatible with HNF and can improve the performance of HNF-based systems, offering valuable insights for green propellant development.

Hypergolic propellants have long been central to spacecraft propulsion because of their storability, reliability and rapid ignition. Conventional systems such as hydrazine derivatives paired with oxidisers like nitrogen tetroxide deliver ignition delays in the order of a few milliseconds but pose serious risks due to extreme toxicity and handling hazards. The search for safer and environmentally friendlier alternatives has therefore become a priority in recent years. This review examines ignition delay times reported in the literature for both conventional and green propellants under ambient experimental conditions. Data were collected from published studies between 2000 and 2025 using major scientific databases, including Scopus, Web of Science, and Google Scholar, and are compared across three categories of propellants: traditional hydrazine-based systems, self-igniting ionic liquids and amines, and systems enhanced with catalytic or reactive promoters. The analysis shows that while conventional propellants remain benchmarks with ignition delays typically between 1 and 5 ms, some new formulations, particularly those containing reactive additives such as borohydrides or iodide salts, are achieving similar or improved performance in laboratory tests. The review also highlights that variability in reported ignition delays often stems from differences in test methods, droplet size, oxidiser concentration, and diagnostic approaches. Beyond performance considerations, attention is given to safety and environmental aspects since several green candidates reduce acute toxicity but introduce other challenges, such as instability or corrosive byproducts. By bringing together data in a comparative format and emphasising methodological limitations, this review aims to support the future design and evaluation of practical green hypergolic propellants.

Computational analysis on film cooling effectiveness over a flat plate using different coolant injection hole geometries are reported. The designed computational setup and flow physics are suitably validated against the existing experimental results for an injection angle of 30°. The present study reports and compares the degree of film cooling effectiveness obtained by the different orientations of the coolant injection holes and their geometry, hole arrangements in the rows and number of rows. The computational domain was designed using Ansys Fluent. The blowing ratio is systematically ranged between 0.67 and 1.67. The performance of a given film cooling scheme is reported in terms of centreline (ηcl) and spatially averaged (η_sa) adiabatic effectiveness. It is observed that for single hole configuration, the semi-elliptic geometry increases the ηcl by ~66.67% up to x/D(ratio of downstream distance from hole to diameter of hole) = 50 at lower blowing ratios (0.67 and 1.00) and by ~50% up to x/D=100 at higher blowing ratios (1.33 and 1.67). For ηsa, an increment of ~200% and ~60% is achieved for all blowing ratios using the triangular and semi-elliptic geometries, respectively. For the multiple row arrangements, the two staggered rows delivered an increment in ηcl of ~77% up to x/D=50 and ~54% up to x/D=100. The two staggered configurations at 0° gave the highest effectiveness increment of ~177% up to x/D=50 while it was ~100% for up to x/D=100. Results indicate that the triangular geometry shows the highest values of the film cooling effectiveness, and a semi- elliptic geometry utilizes ~50% of the coolant mass flow than other coolant injection hole geometries while delivering higher effectiveness values.

Polymer-based composites have been drawing the attention of the research community for many decades, not only in academia but also in industry. However, continuously increasing environmental concerns have led the researchers to focus on natural composite materials. This is a challenge for researchers to develop a natural composite without compromising the composites’ excellent mechanical properties and tribological performance. In this research, coir and sugarcane are selected as the natural fillers, and epoxy resin has been chosen for matrix material. To look into the crystallinity of composites, XRD analysis was done. In addition, a mechanical study was done to look at the manufactured composites’ tensile and flexural characteristics. The tribological performance (i.e., wear rate and friction coefficient) of the composite samples is investigated by using a pin-on-disc setup. The parameters such as filler loading and normal load affecting the tribological performance of epoxy-based natural composites are studied. The results show that the wear and friction characteristics of the composite reinforced with sugarcane and coir were 10.78% and 57.80% lower than those of the neat composite, respectively.

The vibration and damping characteristics of the laminated composite cylindrical sandwich shell with carbon nanotube reinforced magnetorheological elastomer (CNT-MRE) core is presented in this article. Higher order shear deformation theory (HSDT) based on finite element (FE) formulation is employed to derive the governing equations of motion of the laminated composite cylindrical CNT-MRE sandwich shell. The present HSDT model of the cylindrical CNT-MRE sandwich shell is validated with the ABAQUS model in terms of natural frequencies on cantilever boundary condition. The influence of CNT reinforcement in the MRE layer of the cylindrical sandwich shell is also studied through the structural rigidity. The detailed parametric investigations are performed to study the influence of magnetic field intensities, thickness ratio, radius of curvature and ply orientation on the stiffness and damping behavior of composite cylindrical CNT-MRE sandwich shell.

In this study, the relationships between meteorological parameters (relative humidity, wind speed, temperature, planetary boundary layer, and rainfall) and air pollutants (particulate matter and gaseous pollutants) have been evaluated during a 3-year period from 2019 to 2021. Diffusion and dispersion of air contaminants were significantly influenced by meteorology over the capital city. The results of correlation matrix and principal component analysis (PCA) suggest a season’s specific influence of meteorological parameters on atmospheric pollutants’ concentration. Temperature has the strongest negative impact on pollutants’ concentration, and all the other studied meteorological parameters negatively (reduced) as well as positively (increased) impacted the air pollutants’ concentration. A two-way process was involved during the interaction of pollutants with relative humidity and wind speed. Due to enhanced moisture-holding capacity during non-monsoon summers, particles get larger and settle down on the ground via dry deposition processes. Winter’s decreased moisture-holding capacity causes water vapour coupled with air contaminants to remain suspended and further deteriorate the quality of the air. High wind speed helps in the dispersion and dilution but a high wind speed associated with dust particles may increase the pollutants’ level downwind side. The PM_2.5/PM₁₀ variation revealed that the accumulation effect of relative humidity on PM_2.5 was more intense than PM₁₀. Daily average location-specific rainfall data revealed that moderate to high rainfall has a potential wet scavenging impact on both particulate matters and gaseous pollutants.

Every year at the onset of winter season (October–November), crop residue/parali/stubble burning starts in Punjab and Haryana, leading to heavy air pollution in Delhi, and adversely affecting human and environmental health. During this time, the combination of unfavourable meteorological conditions, additional emissions from stubble burning, and firework activities in this area causes the air quality to further deteriorate. In this study, we have attempted to understand the influence of parali and firecracker incidents on air pollutants’ variability over Delhi during the last three years (2020 to 2022). For this purpose, daily average particulate matter and gaseous pollutants data were fetched from the Central Pollution Control Board (CPCB), and daily total fire counts and fire radiative power (FRP) data were retrieved from NASA’s Fire Information for Resource Management System (FIRMS). A bigger area of severe burning is suggested by higher FRP values and higher fire counts in the middle of November in all the years considered. Three years satellite-based FIRMS data over Punjab and Haryana show the highest number of active fire counts in 2021 (n = 80,505) followed by 2020 (n = 75,428), and 2022 (n = 49,194). More than 90% parali burning incidents were observed in Punjab state only despite the considerable variability in numbers among the years. The significant effect of parali burning was seen on pollutant concentration variability. As the number of fire count increases or decreases in Punjab and Haryana, there is a corresponding increase or decrease in the particulate matter concentration with a time lag of few days (1 to 2 days). The trend in backward air mass trajectories suggests that the variable response time of pollutants’ concentration is due to local and distant sources with different air mass speeds. Our estimates suggest that stubble burning contributes 50–75% increment in PM_2.5 and 40 to 45% increase in PM₁₀ concentration between October and November. A good positive correlation between PM_2.5, PM₁₀, NO_X, and CO and fire counts (up to 0.8) suggests a strong influence of stubble burning on air quality over Delhi. Furthermore, the firecracker activities significantly increase the concentration of particulate matter with ~100% increment in PM_2.5 and ~55% increment in PM₁₀ mass concentrations for a relatively shorter period (1 to 2 days).

This paper presents the dynamic responses of sandwich beams with 3D printed thermoplastic composite face sheets and multi-walled carbon nanotubes reinforced magnetorheological elastomer (MWCNT-MR elastomer) cores under non-uniform magnetic fields. A higher-order beam theory (HoBT) is employed to express the beam‘s displacement field. The governing equations of the 3D printed thermoplastic sandwich beam are derived using Lagrange‘s principle and discretized by the finite element method. The validity of the present method is confirmed through comparison with the results available in the literature. The stiffness and damping characteristics of the 3D printed thermoplastic sandwich beam are investigated in relation to support conditions, non-homogeneous magnetic flux, and core-face sheet thickness ratio.