Search Results (14)

Utilizing the pyrolysis reaction of endothermic hydrocarbon fuels to provide thermal protection for hypersonic vehicles is a feasible approach. The introduction of catalysts or cracking-initiating additives could promote hydrocarbon fuel cracking and increase the reaction heat sink. Catalysts such as ZSM-5 zeolite, Al₂O₃, and precious metals were commonly used for hydrocarbon fuel cracking. By optimizing their pore structure and acidity, their catalytic cracking performance can be effectively improved. These catalysts can function not only as catalytic coatings but also be dispersed in the fuel to act via quasi-homogeneous catalytic cracking. Additionally, small-molecule and macromolecular additives could crack at lower temperatures to generate active free radicals, thereby initiating the cracking of hydrocarbons and increasing the reaction heat sink. Under the conditions of a reaction temperature of 650–750 °C, a pressure of 3–5.5 MPa, and a fuel flow rate of 1 g/s, quasi-homogeneous catalysts can enhance the heat sink of hydrocarbon fuel cracking by 5–21%, while cracking-initiating additives can enhance it by 5.6–8.6%. Therefore, based on the different action modes of catalysts or additives, this review summarizes the recent research on improving the cracking of endothermic hydrocarbons from three aspects: coating catalysts, quasi-homogeneous catalysts, and cracking-initiating additives. Subsequently, the potential challenges of each approach in practical applications are analyzed. Furthermore, based on the current research findings, we outline future research directions with the expectation of facilitating the advancement of efficient cracking technologies for endothermic hydrocarbons. Full article

Hydrocarbon fuels are extensively employed as coolants in the regenerative cooling systems of scramjet engines. However, the pyrolytic coking of hydrocarbon fuels at high temperatures introduces complex adverse effects on the flow and cooling processes. In this study, a numerical model was developed to investigate the coupling processes of fluid flow, heat transfer, pyrolysis and pyrolytic coking in the heated tube, under both a constant outer wall heat flux of 1.8 MW/m² and a constant outer wall temperature of 1150 K. The multi-step pyrolytic reaction mechanism and the kinetic coking model were applied to simulate the pyrolytic coking processes of RP-3. The results reveal that the amounts of catalytic coking and lateral growth exhibit significant differences in magnitude, as well as in their spatial and temporal variations. Under a constant outer wall heat flux, coking evidently increases the outer wall temperature and thermal resistance, leading to a narrowed flow passage and a reduction in the residence time and RP-3 conversion rate. Under a constant outer wall temperature, coking decreases the heat absorption flux, resulting in a lower fluid temperature, which primarily affects the efficiency of the endothermic pyrolytic reaction. The results obtained in this research can provide practical insights for the development of regenerative cooling technology. Full article

Dry reforming of methane and ethanol is a promising catalytic process for the conversion of carbon dioxide and hydrocarbon feedstocks into synthesis gas (H₂/CO), which serves as a key platform for the production of fuels and chemicals. Over the past decade, substantial progress has been achieved in the design of catalysts with enhanced activity and stability under the demanding conditions of these strongly endothermic reactions. This review summarizes the latest developments in catalyst systems for DRM and EDR, including Ni-based catalysts, perovskite-type oxides, MOF-derived materials, and high-entropy alloys. Particular attention is given to strategies for suppressing carbon deposition and preventing metal sintering, such as oxygen vacancy engineering in oxide supports, rare earth and transition metal doping, strong metal–support interactions, and morphological control via core–shell and mesoporous architectures. These approaches have been shown to improve coke resistance, maintain metal dispersion, and extend catalyst lifetimes. The review also highlights emerging concepts such as multifunctional hybrid systems and innovative synthesis methods. By consolidating recent findings, this work provides a comprehensive overview of current progress and future perspectives in catalyst development for DRM and EDR, offering valuable guidelines for the rational design of advanced catalytic materials. Full article

A high-temperature gas plasma scheme using methane/air/K₂CO₃ mixed combustion is proposed for the application background of hypersonic aircraft. The actual combustion temperature was calculated by ANSYS Chemkin Pro software; the various components of the combustion reaction were determined; and the function between temperature and electrical conductivity was established, revealing the variation law of ionization decomposition of K₂CO₃ ionized seeds with gas temperature. At 1500 K, K₂CO₃ ionized seeds are close to complete ionization. Increasing the mass fraction of K₂CO₃ ionized seeds will enhance the endothermic effect of K₂CO₃ seed ionization decomposition. Under the same residual gas coefficient conditions, the combustion equilibrium temperature will correspondingly decrease. The increase in initial combustion temperature results in an approximately linear increase in equilibrium temperature and conductivity. With the increase in initial pressure, the equilibrium temperature of gas shows a logarithmic growth trend, while conductivity gradually decreases and the gradient of change gradually slows down. This study provides a new method for evaluating the ionization characteristics of high-temperature gas plasma formed by potassium carbonate (K₂CO₃) as ionization seed, and hydrocarbon fuel (CxHy) combined with air. Full article

With the in-depth research on hypersonic aerodynamics and hypersonic propulsion technology, humans are growing closer to space travel. Recent studies have shown that the pre-cooled air-turborocket (ATR) or turboexpander engines are some of the potential propulsion methods for reusable space vehicles and single stage-to-orbit (SSTO) missions because they have a high specific impulse at low Mach numbers, which can overcome the problem of the “thrust gap” in turbine-based combined-cycle (TBCC) engines. The ATR engine needs an additional oxidizing agent and the turboexpander engine usually uses hydrogen as fuel, which has low energy density and poor safety. To address this problem, this paper proposed a high-energy-density (HED) hydrocarbon-fueled turboexpander engine, and its feasibility has been proven through a simplified thermodynamic model. Through detailed thermodynamic analysis based on the energy and pressure balance, this paper analyzed the performance characteristics of the engine to evaluate its capacity to work in a wide speed range at low Mach numbers. The results show that the endothermic hydrocarbon-fueled turboexpander engine has good specific impulse in Mach 0∼4 at an equivalence ratio of 0.7∼1.3, and the turboexpander engine can be combined with the dual-mode scramjet and become an efficient acceleration method for SSTO missions and the reusable spacecraft. Full article

This study presents results of predicting the transport properties of hydrocarbon aviation fuels and their decomposed products after pyrolysis. Twenty-seven pure substances and two types of mixture, including both low and high molecular weight hydrocarbons as well as hydrogen, are considered. The specified temperature and pressure ranges, 300 to 1000 K and 0.1 to 5.0 MPa, respectively, correspond to representative operating conditions of a hydrocarbon aviation fuel that circulates as a coolant in the regenerative cooling system of a hypersonic vehicle and include the critical temperatures and pressures of most of the hydrocarbon fuels of interest. Four methods are adopted for the prediction of viscosity and thermal conductivity; the Brule-Starling method is used to predict viscosity, the Modified Propane TRAPP method for thermal conductivity, and the Methane TRAPP, Propane TRAPP, and Chung et al. methods are used for both transport properties. A comparison of the total average values concludes that the Chung et al. and Brule-Starling methods perform best in predicting the viscosity of all substances ranging from hydrogen to high molecular weight hydrocarbons in the temperature and pressure ranges specified in the current study. The quantified comparison by the total average also confirms that the Modified Propane TRAPP method best predicts the thermal conductivity of all of the 29 substances over the set temperature and pressure ranges, although the Propane TRAPP and Chung et al. methods offer a similar level of accuracy. Full article

The integration of active cooling systems in super or hypersonic aircraft using endothermic hydrocarbon fuels is considered an effective way to relieve the thermal management issues caused by overheating. When the temperature of aviation kerosene exceeds 150 °C, the oxidation reaction of fuel is accelerated, forming insoluble deposits that could cause safety hazards. This work investigates the deposition characteristic as well as the morphology of the deposits formed by thermal-stressed Chinese RP-3 aviation kerosene. A microchannel heat transfer simulation device is used to simulate the heat transfer process of aviation kerosene under various conditions. The temperature distribution of the reaction tube was monitored by an infrared thermal camera. The properties and morphology of the deposition were analyzed by scanning electron microscopy and Raman spectroscopy. The mass of the deposits was measured using the temperature-programmed oxidation method. It is observed that the deposition of RP-3 is highly related to dissolved oxygen content (DOC) and temperature. When the outlet temperature increased to 527 °C, the fuel underwent violent cracking reactions, and the structure and morphology of deposition were significantly different from those caused by oxidation. Specifically, this study reveals that the structure of the deposits caused by short-to-medium term oxidation are dense, which is different from long-term oxidative deposits. Full article

Redox materials have been investigated for various thermochemical processing applications including solar fuel production (hydrogen, syngas), ammonia synthesis, thermochemical energy storage, and air separation/oxygen pumping, while involving concentrated solar energy as the high-temperature process heat source for solid–gas reactions. Accordingly, these materials can be processed in two-step redox cycles for thermochemical fuel production from H₂O and CO₂ splitting. In such cycles, the metal oxide is first thermally reduced when heated under concentrated solar energy. Then, the reduced material is re-oxidized with either H₂O or CO₂ to produce H₂ or CO. The mixture forms syngas that can be used for the synthesis of various hydrocarbon fuels. An alternative process involves redox systems of metal oxides/nitrides for ammonia synthesis from N₂ and H₂O based on chemical looping cycles. A metal nitride reacts with steam to form ammonia and the corresponding metal oxide. The latter is then recycled in a nitridation reaction with N₂ and a reducer. In another process, redox systems can be processed in reversible endothermal/exothermal reactions for solar thermochemical energy storage at high temperature. The reduction corresponds to the heat charge while the reverse oxidation with air leads to the heat discharge for supplying process heat to a downstream process. Similar reversible redox reactions can finally be used for oxygen separation from air, which results in separate flows of O₂ and N₂ that can be both valorized, or thermochemical oxygen pumping to absorb residual oxygen. This review deals with the different redox materials involving stoichiometric or non-stoichiometric materials applied to solar fuel production (H₂, syngas, ammonia), thermochemical energy storage, and thermochemical air separation or gas purification. The most relevant chemical looping reactions and the best performing materials acting as the oxygen carriers are identified and described, as well as the chemical reactors suitable for solar energy absorption, conversion, and storage. Full article

One of the main issues that has limited the use of hydrogen as an energy vector for a long time is its low energy density per unit of volume. Alternative chemical storage methods have been developed in recent years to overcome the limitations associated with compressed or liquified hydrogen storage. One of these is the Liquid Organic Hydrogen Carrier (LOHC), which utilizes organic hydrocarbons that can capture hydrogen (through an exothermic hydrogenation reaction) and release hydrogen (through an endothermic dehydrogenation reaction). In this paper, a 0D model of an internal combustion engine fueled with a mixture of hydrogen and methane was used to investigate whether the enthalpy of the exhaust gases can balance the heat rate required to self-sustain the dehydrogenation stage. Two LOHC+ compounds were considered, namely, Perhydro-dibenzyltoluene and Perhydro-N-Ethylcarbazole. Four different hydrogen-to-methane ratios were considered, assuming an engine maximum brake power ranging from 500 to 6000 RPM. An energy balance was performed, balancing the dehydrogenation heat rate and the exhaust gas cooling heat rate, in order to establish the minimum temperatures of the exhaust gases required to self-sustain the LOHC+ dehydrogenation. We demonstrated that the minimum exhaust temperatures required to self-sustain the process in different running regimes and at different hydrogen-to-methane ratios are lower than literature and experimental exhaust temperatures. Full article

A model of a NUAA-PTRE pre-cooled air turbine engine was established. The design point parameters of the engine were optimized, including the pressure ratio, air flow rate of the compressor, efficiency, throat area, and efficiency of the turbine. The air flow rate at the engine operating point was 142.73 kg/s. High performance of the key components under a wide range of working conditions was realized after optimization. To achieve the indicators of the overall scheme, adaptability studies of key components were conducted. A three-stage variable geometry design was applied to the inlet. The pre-cooler was optimized with a power-to-weight ratio of over 100 kW/kg and a compactness of 278 m²/m³. The built-in rocket gas generator and dual-component injector were developed, and the combustion and heat transfer processes were simulated. The overall optimization design of the NUAA-PTRE and the adaptive design of the components were completed, and high performance of the engine in a wide range of flight conditions at Ma 0~5 and altitude 0~25 km was achieved. Full article

The mixing process and distribution characteristics of a supercritical endothermic hydrocarbon fuel (EHF) jet injected into a supersonic crossflow were investigated by experimental and numerical methods, respectively. The schlieren system and acetone planar laser-induced fluorescence (PLIF) optical system were used to capture the flow-field structural characteristics and instantaneous plume. The mixture and real gas models were employed to calculate the interaction of a transverse jet and supersonic crossflow and reveal a good accuracy with the experimental results. The mixing efficiency and total pressure loss were analyzed based on the numerical results. The results indicate that the supercritical-state EHF directly changes to a gaseous state as it enters the supersonic crossflow from the injector. The EHF jet plume boundary increases with the increasing momentum flux ratio (q). As the streamwise and spanwise distance increases, the traverse heights and expand width increase, and the EHF jet plume presents a semicircle shape in the cross-sectional plane. With the increase in the traverse direction, the concentration distribution shows a fast and then slow power exponential decreasing law; the highest concentration point starts from the near-wall region and rises in the transverse direction with the flow distance increasing. For the same injection condition, the higher the inflow Mach number, the higher the mixing efficiency. For the same Ma, the mixing efficiency is better for the case with low injection pressure and high injection temperature. The total pressure loss is greater in the higher Ma, and high injection pressure conditions cause greater total pressure loss. Full article

In order to explore co-production alternatives, a once-through process for CO₂ hydrogenation to chemicals and liquid fuels was investigated experimentally. In this approach, two different catalysts were considered; the first was a Cu-based catalyst that hydrogenates CO₂ to methanol and CO and the second a Fisher–Tropsch (FT) Co-based catalyst. The two catalysts were loaded into different reactors and were initially operated separately. The experimental results show that: (1) the Cu catalyst was very active in both the methanol synthesis and reverse-water gas shift (R-WGS) reactions and these two reactions were restricted by thermodynamic equilibrium; this was also supported by an Aspen plus simulation of an (equilibrium) Gibbs reactor. The Aspen simulation results also indicated that the reactor can be operated adiabatically under certain conditions, given that the methanol reaction is exothermic and R-WGS is endothermic. (2) the FT catalyst produced mainly CH₄ and short chain saturated hydrocarbons when the feed was CO₂/H₂. When the two reactors were coupled in series and the presence of CO in the tail gas from the first reactor (loaded with Cu catalyst) significantly improves the FT product selectivity toward higher carbon hydrocarbons in the second reactor compared to the standalone FT reactor with only CO₂/H₂ in the feed. Full article

Solar thermochemical processes have the potential to efficiently convert high-temperature solar heat into storable and transportable chemical fuels such as hydrogen. In such processes, the thermal energy required for the endothermic reaction is supplied by concentrated solar energy and the hydrogen production routes differ as a function of the feedstock resource. While hydrogen production should still rely on carbonaceous feedstocks in a transition period, thermochemical water-splitting using metal oxide redox reactions is considered to date as one of the most attractive methods in the long-term to produce renewable H₂ for direct use in fuel cells or further conversion to synthetic liquid hydrocarbon fuels. The two-step redox cycles generally consist of the endothermic solar thermal reduction of a metal oxide releasing oxygen with concentrated solar energy used as the high-temperature heat source for providing reaction enthalpy; and the exothermic oxidation of the reduced oxide with H₂O to generate H₂. This approach requires the development of redox-active and thermally-stable oxide materials able to split water with both high fuel productivities and chemical conversion rates. The main relevant two-step metal oxide systems are commonly based on volatile (ZnO/Zn, SnO₂/SnO) and non-volatile redox pairs (Fe₃O₄/FeO, ferrites, CeO₂/CeO_2−δ, perovskites). These promising hydrogen production cycles are described by providing an overview of the best performing redox systems, with special focus on their capabilities to produce solar hydrogen with high yields, rapid reaction rates, and thermochemical performance stability, and on the solar reactor technologies developed to operate the solid–gas reaction systems. Full article

This article provides a comprehensive overview of the work to date on the two‑step solar H₂O and/or CO₂ splitting thermochemical cycles with Zn/ZnO redox reactions to produce H₂ and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-step cycle encompasses: (1) The endothermic dissociation of ZnO to Zn and O₂ using concentrated solar energy as the source for high-temperature process heat; and (2) the non-solar exothermic oxidation of Zn with H₂O/CO₂ to generate H₂/CO, respectively; the resulting ZnO is then recycled to the first step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life cycle and economic analyses. Full article