Fuel Heat Sink Research Articles

Heat transfer characterization of SCO2 in non-uniformly heated rectangular cooling tubes under large mass flow and heat flux conditions

A Thermoelectric Conversion System (TECS) with SCO2 as the circulating mass can effectively mitigate the fuel heat sink and electrical energy shortage problems of hypersonic vehicles. However, there is still a lack of research on the use of SCO2 in the harsh thermal conditions in scramjet. In this paper, the heat transfer mechanism of SCO2 in rectangular cooling tubes are numerically analyzed for the first time based on the actual working environment of scramjet. The effects of uneven heat flux (q) axial and circumferential allocations and circumferential and axial tilting of the tube are innovatively considered. Meanwhile, we analyze the heat transfer mechanism of SCO2 under different operating parameters. The results show that the uneven allocation of axial q can suppress the heat transfer deterioration (HTD), and the overall heat transfer coefficient (HTC) can be increased by 11.68 % when the q allocation is Gaussian. The increase of the tube inclination angle can improve its heat transfer performance, and the local HTC can be increased by up to 5.64 % when θ2 = 180°.Increasing the mass flow rate (G) and inlet temperature (Tin) can increase the overall HTC of the tube. This paper can provide guidance for the design and improvement of TECS.

Design and analysis of a novel thermal management system for serving next-generation aircraft with megawatt-level heat loads

Due to the development of electronics and high-energy pulse devices, in conjunction with the increasing flight speeds, the instantaneous heat load of next-generation aircraft will reach the megawatt level, which poses severe challenges for thermal management. To improve the heat dissipation capability, this paper presents a novel thermal management system (TMS) employing liquefied natural gas (LNG). This TMS design incorporates four merits: LNG and fuel share the heat load of electronics which dramatically enhances the mission time; the air circulation subsystem selects different combinations of heat sinks depending on the engine's operational state; LNG spray cooling efficiently handles the heat load of directed energy weapons; the heat sinks release the cooling capacity in a temperature gradient to maximize efficiency. The performance of the TMS is verified in a harsh flight profile. The selection of an appropriate return location and the storage of low-temperature fuel can enhance the efficiency of the fuel heat sink. An effective means of improving the vapor compression subsystem's efficiency is increasing the withstand temperature of the electronics. The introduction of LNG extends mission time by more than three times with minor fuel penalties. The potential for utilizing turbines to enhance LNG cooling efficiency is explored.

Improve the thermal performance of precooler by enhancing the utilization of chemical heat sink: Refined design method and characteristic analysis

The chemical heat sink of the coolant plays a crucial role in enhancing the performance of the precooler, which affects the overall performance of the air-breathing precooled engines. The conventional thermal design method for precoolers cannot accurately evaluate the chemical heat sink of coolants. To address this crucial issue, this paper proposes a refined model that considers the chemical reaction processes of n-Decane, based on a two-dimensional discretization unit model and the plug flow reactor model incorporating molecular-level chemical reaction mechanisms. The validation of this model is conducted by comparing it with publicly accessible data and computational fluid dynamics simulations, thereby demonstrating its excellent accuracy. Subsequently, an analysis is conducted on the factors influencing the chemical heat sink release of the coolant within the precooler, and enhanced design criteria for optimizing chemical heat sink utilization are proposed. Building upon these considerations, the performance of a precooler with a design point of Mach number 5 under off-design conditions was analyzed. The findings indicate that employing rational design methods can enhance the chemical heat sink efficiency of endothermic fuels by 8.0%, along with a concurrent 10.3% increase in the total heat sink. This underscores the significance of considering the impact of the chemical heat sink of endothermic fuels in the design of precoolers. In the case presented in this paper, the contribution of the chemical heat sink to the total heat sink within the n-Decane precooler could reach 35.3%.

Thermal management of fuel heat sink in aircraft via flow path optimization

With the rapid increase of aircraft thermal loads, efficiently utilizing the fuel heat sink has received widespread attention in recent years. To improve the performance of the aircraft fuel thermal management system (AFTMS), a concept of the fuel heat sink consumption rate (FHSCR) is proposed to assess the system heat dissipation, and an optimization criterion of fuel heat sink is established based on the FHSCR. Besides, a new architecture of the AFTMS with a middle fuel return branch (MFRB) and a recirculation fuel supply branch (RFSB) is designed to enhance the heat dissipation capacity, and unlike previous studies, only the flow path of the fuel supply and return subsystem (FSRS) has been changed here without additional fuel tanks. Moreover, a dynamic optimal controller based on the particle swarm optimization (PSO) algorithm with the minimum variation distance (MVD-PSO) is developed for obtaining the optimal control parameters and eliminating the parameter oscillation, which is applied in the comparison calculations under both a single condition and a complete mission profile. The calculation results show that compared to the original architecture, the new architecture can reduce the FHSCR by 14.16% under the standard condition, and the thermal endurance of the standard and extreme conditions is extended by 37.42% and 19.54%, respectively. In addition, the new architecture exhibits a better thermal management performance during the whole mission as well. To sum up, comprehensively dealing with the waste heat by both the combustion fuel and ram air is crucial for system cooling, and the new architecture improves the heat dissipation capacity of the AFTMS significantly. This paper provides a novel flow path optimization guide for the AFTMS.

Simulation of an aircraft thermal management system based on vapor cycle response surface model

The modern aircraft Thermal Management System (TMS) faces significant challenges due to increasing thermal loads and limited heat dissipation pathways. To optimize TMS during the conceptual design stage, the development of a modeling and simulation tool is crucial. In this study, a TMS simulation model library was created using MATLAB/SIMULINK. To simplify the complexity of the Vapor Cycle System (VCS) model, a Response Surface Model (RSM) was constructed using the Monte Carlo method and validated through simulation experiments. Taking the F-22 fighter TMS as an example, a thermal dynamic simulation model was constructed to analyze the variation of thermal response parameters in key subsystems and elucidate their coupling relationships. Furthermore, the impact of total fuel flow and ram air flow on the TMS was investigated. The findings demonstrate the existence of an optimal total fuel flow that achieves a balance between maximizing fuel heat sink utilization and minimizing bleed air demand. The adaptive distribution of fuel and ram air flow was found to enhance aircraft thermal management performance. This study contributes to improving modeling efficiency and enhancing the understanding of the thermal dynamic characteristics of TMS, thereby facilitating further optimization in aircraft TMS design.

The mechanism of ethanol blending on the variation of chemical heat sink in n-decane thermal cracking process

The cracking of on-board hydrocarbon fuels is a strong endothermic reaction and can provide an additional chemical heat sink in the cooling process of the hypersonic vehicle. However, the cooling capacity of current hydrocarbon fuels can hardly meet the cooling requirements of the hypersonic vehicle at higher flight speeds. Blending ethanol is an effective method to improve the chemical heat sink of hydrocarbon fuels, but the mechanism of ethanol on chemical heat sink is unclear. In this study, n-decane was selected as a model compound of hydrocarbon fuels to investigate the physical and chemical effect of ethanol on the chemical heat sink of n-decane cracking by analyzing the chemical reactions involved through experimental study and chemical dynamic simulation. The results indicate that there is an optimum ethanol blend ratio to achieve the maximum chemical heat sink. The carbon monoxide methanation reaction which is an exothermic reaction can deteriorate endothermic process at 300–375 °C. With ethanol blending ratio above 20 wt%, ethanol vaporization deteriorates chemical heat sink by reducing the residence time in the temperature range of 225–250 °C. Pressure can suppress the reduction of residence time caused by ethanol evaporation and also suppress the positive reaction of ethanol cracking. The kinetic model of ethanol and n-decane mixture cracking was established. The calculated results verify that ethanol cracking (C2H5OH=CO+CH4+H2) and methane cracking (CH4=C+2H2) are dominant reactions in ethanol-assisted n-decane thermal cracking below 475 °C.

Effect of pressure on regenerative cooling process of endothermic hydrocarbon fuel at severe pyrolysis conditions

Regenerative cooling technology with supercritical aviation kerosene as coolant is the optimal thermal management method for advanced aero engines. In order to fill the gap in existing research on the pressure effects at severe pyrolysis, the influence of pressure on the flow field, pyrolysis behaviours, heat transfer, and surface coking are numerically investigated in this study. The results indicate that the velocity-temperature curves at different pressures have two intersections due to the difference in initial pyrolysis temperature, reaction rate, and product distribution. Fuel pyrolysis more easily occurs at high pressure, and elevating pressure improves the fuel heat sink. Besides, a special deterioration of heat transfer is found at high conversion rates because of the combined contribution of weakened primary endothermic reaction and enhanced secondary exothermic reaction. Heat transfer deterioration is delayed at 3.5 MPa due to the high initial pyrolysis temperature and significant flow acceleration. The primary pyrolysis reaction provides more than 80% chemical heat sink and 60% flow acceleration at fully cracked conditions at 5.0 MPa. In addition, inhibiting catalytic coking is the principal method to reduce carbon deposition, and more attention should be paid to carbon deposition under high pressure. The results obtained in this study are expected to provide insights into the selection of operating pressures for advanced aero engines.

Reactive molecular dynamics study on catalytic pyrolysis and steam reforming of hydrocarbon fuel

The strong endothermic capability of catalytic steam reforming highlights its potential for improving the heat sink of hydrocarbon fuels. To explore the complex interaction between catalytic pyrolysis and steam reforming reactions, as well as their contributions to the heat sink of fuels, the reactive force-field molecular dynamics (ReaxFF-MD) simulation is employed in this work to investigate the palladium-catalyzed pyrolysis and steam reforming of n-dodecane (n-C12H26). The results show that pyrolysis reaction supplies C1 and C2 components, and then participates in the steam reforming generating more than 90% of aldehyde groups. Meanwhile, compared to catalytic pyrolysis reaction, the catalytic steam reforming containing 25 n-C12H26 and 300 H2O reduces 40.54% of carbon atoms deposited inside the palladium lattice, and improves the heat sink from 254.18 kcal/mol to 386.03 kcal/mol. Furthermore, our simulated results quantitatively describe the detailed contributions of catalytic pyrolysis and steam reforming to the simulation process. With more H2O added, the proportion of steam reforming gradually increases, which reaches 35.08% in the system containing 25 n-dodecane and 300 H2O. Moreover, the contribution of H atoms in the formation of H2 also indicates the variation in the proportion of steam reforming.

Heat transfer enhancement in a regenerative cooling channel using porous media

The endothermic hydrocarbon fuels play an important role in the thermal management of hypersonic scramjet. However, there often involve serious thermal stratifications in the regenerative cooling channel. The present work conducts a two-dimensional cooling channel numerical simulation with the addition of porous media using a unique global chemical kinetics model to clarify the increase of the total heat sink of hydrocarbon fuels. It is proposed that the addition of porous media is a coupling process, which not only enhances heat transfer, but also will bring resistance to heat. Therefore, the energy source term is included in the numerical simulations, which makes our calculations closer to the actual working condition compared to the previous numerical modeling. The simulated results indicate that compared to the smooth channel, the thermal stratifications are relieved in the cooling channel with the addition of porous media, while the thermal cracking of n-decane is inhibited due to the decrease of the wall temperature. In addition, with the decrease of porosity of porous media, the total heat sink of fuel increases. The heat transfer coupling rule of porous media is studied by placing porous media at different positions, and the optimal placement position is found.

Optimization of Power and Thermal Management System of Hypersonic Vehicle with Finite Heat Sink of Fuel

The scramjet of hypersonic vehicles faces severe high-temperature challenges, but the heat sink available for scramjet cooling is extremely finite. It is necessary to optimize its power and thermal management system (PTMS) with a finite heat sink of hydrocarbon fuel. This paper proposes a two-level optimization method for the PTMS of hypersonic vehicles at Mach 6. The PTMS is based on a supercritical carbon dioxide (SCO2) closed Brayton cycle, and its heat sink is airborne hydrocarbon fuel. System-level optimization aims to obtain the optimal system parameters for the PTMS. The minimum fuel weight penalty and the minimum heat sink consumption of fuel are the optimization objectives. The segmental (SEG) method is used to analyze the internal temperature distribution of fuel–SCO2 heat exchangers in the system-level optimal solution set. This ensures the selected optimal solutions meet the requirement of a pinch temperature difference greater than or equal to 10 °C. Further, the component-level optimization for the fuel–SCO2 heat exchanger is carried out based on the selected optimal solutions. The lightest weight of the heat exchanger and the minimum entropy production are the optimization objectives in this step. Finally, the optimal system parameters and the optimal key component parameters can be searched using this presented two-level optimization method.

Temperature Dynamic Characteristics Analysis and Thermal Load Dissipation Assessment for Airliner Hydraulic System in a Full Flight Mission Profile

This paper deals with the modeling of the thermal load and the simulation of thermal dynamic characteristics for the hydraulic system of a large airliner in a full mission profile. Firstly, the formation mechanism of the thermal load in the hydraulic system is analyzed, and thermal dynamic modeling is conducted of the hydraulic components of an hydraulic system with an immersed heat exchanger employing the lumped parameter thermal node method and oil temperature and power loss of each key node within the hydraulic system within a full mission profile. Then, a thermal dynamic simulation model based on MATLAB/Simulink is established, and the temperatures at the nodes of different components and the absorptive capacity of the fuel heat sink in the thermal management module are calculated. The simulation results show that the thermal management scheme of the heat exchanger, located in the return oil pipeline of the hydraulic piston pump housing and immersed in the central fuel tank, can dissipate the thermal load of the system. This work is of important significance for temperature analysis and thermal load dissipation of the airliner hydraulic system.

Performance comparison of three chemical precooled turbine engine cycles using methanol and n-decane as the precooling fuels

Precooled turbine engines are promising power for next generation in- and trans-atmospheric vehicles. A novel chemical precooling technology was proposed in our previous paper to reduce the fuel consumption by improving the chemical heat sink of fuels. However, the appropriate configuration design for chemical precooled engine cycle has not been revealed. This paper proposed an overall-view analysis method to distinguish the effects of different configurations/parameters on the engine performance, from which the configuration could be parameterized via a unified thermodynamic model. To improve the simulation precision of this model, the heat sink of fuel was measured by test. Through calculation, the results indicated that the utilization of working ability of the heated fuel was an effective way to improve the engine performances, and the cycle adopting both rocket turbine and gas turbine could increase the highest flight Mach number by 7.06%. Besides, the optimal engine performance could be obtained when the equivalence ratio was equal to 1.0. Moreover, the engine performance was more sensitive to air side pressure recovery coefficient of pre-cooler at smaller pressure ratio range; while for the larger pressure ratio, the efficiency of air compressor was the dominant factor.

Pyrolysis and heat sink of an endothermic hydrocarbon fuel EHF-851

A new endothermic hydrocarbon fuel with density of 0.851 g/cm3 (EHF-851) was proposed taking account of the energy density and heat sink of hydrocarbon fuels for the thermal management of advanced aircraft. Sub- and super-critical pyrolysis of EHF-851 was investigated by the electrically heated tube test at 650−750 °C under 0.7–6.0 MPa. The effect of operation parameters (flow rate, pressure and fuel temperature) on the heat sink and detailed pyrolysis products were presented. The heat sink of EHF-851 is 3.32 MJ/kg at 750 °C (6.0 MPa, 2.67 g/s), which is 25 % higher than that of JP-10 but 8 % lower than that of JP-7. The formation of pyrolytic cokes was significantly inhibited attributed to the hydrogen donor effect of decalin in the fuel.

Performance parameters analysis of an organic Rankine cycle for power generation from the heat of cooling scramjet

An organic Rankine cycle (ORC) for power generation system is proposed for cooling scramjet. The heat which must be taken away by fuel coolant from cooling scramjet is converted to other forms of energy to decrease fuel coolant flow. A parametric study of an ORC power generation system has been performed. The multiplication ratio of fuel heat sink, the efficiency and output power of the system changing with the condenser outlet fuel coolant temperature are evaluated. The results show that the optimal condenser outlet fuel coolant temperature is 510K in a certain working condition, and the multiplication ratio of fuel heat sink is 0.0635, the efficiency of the system is 11.74% and the output power is 35.13kW. The effect of the cycle pressure ratio on the efficiency, output power and the multiplication ratio of fuel heat sink is also analyzed and it has a big significant influence. It is known through thermodynamic analyses that ORC power generation system for cooling scramjet would reduce the fuel coolant flow and give some output power for hypersonic vehicle.

Catalytic steam reforming and heat sink of high-energy-density fuels: Correlation of reaction behaviors with molecular structures

This work investigated the steam reforming (SR) performance of high-energy–density (HED) fuels including exo-tetrahydrodicyclopentadiene (exo-THD), exo-tetrahydrotricyclopentadiene (exo-THT), 1,3-dimethyladamantane (DMA) and quadricyclane (QC), aiming to provide sufficient heat sink for hypersonic flight. The fuel conversion decreases in the order of QC > DMA ≈ exo-THD > exo-THT, while the molecular-structure-dependent catalyst stability trend is DMA > exo-THD > QC ≈ exo-THT, which are related to the H/C value, carbon deposition and exposure of active Ni species after carbon deposition. Importantly, the catalytic SR reaction can significantly improve the total heat sink of HED fuels. Especially, DMA and exo-THD with higher H/C and (H/C)*Ma exhibit excellent performance on activity and stability, on which high total heat sink, total heating value and coke-resistance are achieved. This work provides the molecule-SR heat sink relationship for the design of the effective cooling system for the hypersonic flight.

Strategically designed macromolecules as additives for high energy-density hydrocarbon fuels

To improve oxidative stability and heat sink of hydrocarbon fuels, a series of versatile macromolecular additives, BHPEI and CBHPEI, were synthesized by modification of hyperbranched poly(ethyleneimine) (HPEI). These macromolecules were used as circumstance-dependent additives in JP-10, a high energy–density hydrocarbon fuel. Each strategically designed macromolecule serves not only as a radical scavenger to improve the thermal-oxidative stability of hydrocarbon fuels at relatively low temperature, but also as a cracking initiator for heat sink enhancement as the temperature rises. According to the ASTM E1858, with the addition of BHPEI-10K at 500 ppm, the oxidation induction time of JP-10 under 175 °C could increase from 9.3 min to 14.8 min. The insoluble deposits could be reduced by 73% with the addition of 500 ppm BHPEI-10K according to accelerated oxidation tests. The superior antioxidation capability of macromolecular antioxidants were further elucidated by density functional theory (DFT) calculations. Furthermore, the BHPEI-10K performed decently as a macromolecular initiator for supercritical cracking of JP-10, with a dosage of 0.1 wt%, the conversion of JP-10 at 675 °C can be elevated from 16.4% to 33.4% and the corresponding heat sink can be improved from 1.98 MJ/kg to 2.15 MJ/kg.

Analysis of the maximum flight Mach number of hydrocarbon-fueled scramjet engines under the flight cruising constraint and the combustor cooling requirement

Scramjet is the optimal propulsion system for hypersonic vehicles, and it is important to study its maximum flight Mach number. Upper limit and its influence factors of the flight Mach number of dual-mode scramjet used in hypersonic vehicles are investigated in this paper. Scramjet performance analysis model with the constant-area heating process, cooling requirement analysis model of the combustor and cruise model of the scramjet-powered hypersonic vehicle are established. Specific impulse of dual-mode scramjet engine with hydrocarbon fuel is similar to that of liquid oxygen kerosene rocket engine when the freestream Mach number is above 10. The ratio of hypersonic vehicle reference area to scramjet inlet capture area is introduced to establish the size relationship between the scramjet engine and the hypersonic vehicle. Considering the balance of thrust and drag, smaller ratio of hypersonic vehicle reference area to scramjet inlet capture area leads to higher flight Mach number that hypersonic vehicle can cruise. When the angle of attack is 10 degrees, the ratio of hypersonic vehicle reference area to scramjet capture area should be less than 5.5 to ensure that the vehicle can work at Mach 8. The maximum length to diameter ratio of the combustor is used to indicate active cooling requirements, and it is less than 5 under the cooling requirement when flight Mach number is above 9. Reducing the heat flux at the combustor wall and increasing the fuel heat sink is helpful to increase the allowable combustion chamber length, so as to increase the maximum flight Mach number of the scramjet engine on the premise of meeting thermal protection requirement.

Experimental Investigation on Pyrolysis of n-Decane Initiated by Nitropropane under Supercritical Pressure in a Miniature Tube

Adding an initiator is an effective method of promoting hydrocarbon pyrolysis and improving the heat sink of fuels. Nitropropane was proposed as an initiator with good performance, owing to its lower reaction activation energy for C–N bond cleavage. To study the effects of this initiator on hydrocarbon pyrolysis, a miniature tube reactor that can simulate a real heating procedure in an aeroengine was used to investigate the n-decane pyrolysis with and without nitropropane under experimental supercritical conditions. The results demonstrate that the nitropropane initiator promotes the pyrolysis of fuel as it flows through a tube with a large length–diameter ratio within a certain temperature range. The initial decomposition temperature of n-decane is reduced by approximately 100 K, and the increase in the conversion leads to a higher heat sink for n-decane, which can result in decreases in the fuel and reactor temperatures under the same heating condition and within the effective temperature range. A stronger promoting effect can be achieved by increasing the concentration of the nitropropane initiator. The variation laws for the n-decane pyrolysis reaction rate along the flow reactor are changed by the initiator, the presence of nitropropane greatly accelerates the pyrolysis reaction of fuel at a lower temperature, and the opposite tendency appears as the fuel temperature increases, which is caused by the consumption of the initiator. In addition, the selectivity of methane, propane, and alkenes, especially ethylene, increases because of the propyl radical generated by the C–N dissociation of nitropropane before the initiator is consumed.

Thermal Cracking of Endothermic Hydrocarbon Fuel in Regenerative Cooling Channels with Different Geometric Structures

The chemical heat sink of endothermic hydrocarbon fuels (EHFs) is generally dependent on its thermal cracking in the cooling channel, which is accompanied and limited by the formation of carbon deposit. In this work, HF-1 (a kerosene-based EHF) was electrically heated in the rectangular, square, and circular channels with the same cross-sectional area under 3.5 MPa to study the effect of cooling channel geometric structures on the thermal cracking and carbon deposition behaviors. It was found that under similar conditions (inlet flow rate of fuel, pressure, outlet temperature), conversions of HF-1 in both rectangular and square channels were slightly higher than that in the circular one with high selectivity to methane but lower selectivities to the primary cracking products (such as 1-hexene and 1-heptene, etc.). In addition, more carbon deposits were formed in the rectangular and square channels, especially around the corners of channels. Based on the CFD simulation, the possible reasons should be ascri...

Study on Chemical Heat Sink of Liquid Hydrocarbon Fuel under Supercritical Condition

Study on Chemical Heat Sink of Liquid Hydrocarbon Fuel under Supercritical Condition