Deep Cryogenic Research Articles

Energy Transition in Aviation: The Role of Cryogenic Fuels

Aviation is the backbone of our modern society. In 2019, around 4.5 billion passengers travelled through the air. However, at the same time, aviation was also responsible for around 5% of anthropogenic causes of global warming. The impact of the COVID-19 pandemic on the aviation sector in the short term is clearly very high, but the long-term effects are still unknown. However, with the increase in global GDP, the number of travelers is expected to increase between three- to four-fold by the middle of this century. While other sectors of transportation are making steady progress in decarbonizing, aviation is falling behind. This paper explores some of the various options for energy carriers in aviation and particularly highlights the possibilities and challenges of using cryogenic fuels/energy carriers such as liquid hydrogen (LH2) and liquefied natural gas (LNG).

Test Data Analysis of the Vented Chill, No-Vent Fill Liquid Nitrogen CRYOTE-2 Experiments

NASA is interested in developing efficient methods with which to transfer cryogenic propellants to enable future in-space cryogenic propellant vehicles, particularly the cryogenic fuel depot. The process of transferring cryogenic propellants between two vessels in a reduced gravity environment is complicated by the low normal boiling point of cryogens, high propensity for boiling during tank chilldown, and the fact that liquid cannot be transferred with the receiver tank vent valve open to space. This paper presents test data analysis of the liquid nitrogen vented chill, no-vent fill (NVF) experiments on the CRYOTE-2 tank. 53 tests were conducted, and while not originally intended, were performed in a somewhat parametric fashion. Performance between three different injectors are compared, as well as the effect of initial receiver tank wall temperature, receiver tank fluid initial condition, supply pressure, mass flow rate, and trigger point on the NVF process. From in-depth test data analysis, the highest performing injector based on maximizing evaporation heat and mass transfer between droplets and ullage as well as condensation heat transfer at the liquid/vapor interface, was the 3-spray injector.

Performance Evaluation of Electrical Discharge Machining using Ultrafine-Grained Cu Electrodes Processed by Equal Channel Angular Pressing and Deep Cryogenic Treatment

The role of the electrode in electric discharge machining (EDM) performance is crucial because it has an impact on the geometrical accuracy, machining efficiency and surface finish of the machined components. In the present work, a new technical approach combining equal channel angular pressing (ECAP) and deep cryogenic treatment (DCT) was put forward to manufacture copper electrodes for enhancing the machining characteristics of electric discharge machining (EDM). Effects of the ECAP, the ECAP + DCT on the EDM performances including the electrode wear rate (EWR), the workpiece corner sharpness (WCS), the surface roughness (Ra) and the surface characteristics of EDM workpieces have been investigated. The EWR after the ECAP and the ECAP + DCT was reduced to the minimum after two passes of ECAP. The EWR and WCS after the ECAP + DCT were less than that after the ECAP due to the higher hardness and electrical conductivity. The Ra of EDM workpieces using electrodes processed by the ECAP + DCT was slightly less than that after ECAP. An analogous Hall–Petch relation between the Ra of EDM workpieces and the grain size of electrodes was observed, indicating that ultrafine-grained electrodes processed by ECAP and the additional DCT would enhance the surface finish. The surface finish of EDM workpieces was discussed based on the features of the surface morphology.

Investigation of internal flow of Cryogenic injection

As part of an effort to understand the conditions for the ignition of cryogenic propellants in the low pressure environment, we conducted a research of internal flow of cryogenic jet. In this paper, the experimental investigation was exerted focusing on the qualitative morphology study of the cryogenic flow inside the jet injectors. The test facilities were carefully designed and allow for visualization and characterization of the flow. The results show a strong dependence of mass flow rate on the fluid temperature. The two-phase flow was observed even for a long time chilling down of the injector. The Jacob number is proved to be a good indicator for the flow regimes, and the bubbles are present in the flow every time. The injector geometry has an influence on the flow rate, with the tapered injector demonstrating a higher flow rate than the sharp one.

Experimental analysis of thermal behavior in cryogenic propellant tank with different pressurants

The thermal behavior of cryogenic propellant tanks is crucial issue in the operation of cryogenic propulsion systems. Herein, ground experiments were conducted in a 600-mm-diameter cryogenic tank filled with liquid nitrogen. As pre-pressurants, gaseous helium and gaseous nitrogen (of the same species as the liquid), were used to investigate its effect in accordance with actual propulsion systems. The tank was sealed after pre-pressurization to observe the self-pressurization. The evaporation rate and heat flow in the tank were estimated based on pressure and temperature measurements. In addition, the axial liquid temperature distribution was obtained through the liquid draining from the tank bottom, and a thermal stratification model was developed. These results demonstrated that the type of pre-pressurant significantly affected the thermal behavior in the tank. A higher evaporation rate and higher liquid internal energy rise rate with a thicker thermal layer were observed in the helium pre-pressurization case. The lower nitrogen partial pressure in the helium case enhanced the vaporization and growth of the thermal layer. Estimation of the power balance in the tank demonstrated that not only the ullage but also the heat mass of the tank provided heat for the evaporation and thermal layer. The evaporation occurs mainly at the contact point between the tank skin and liquid surface. The nitrogen vapor rises in a thin layer along the tank skin because of buoyancy under nitrogen pre-pressurization; however, buoyancy is lower under helium pre-pressurization, and a radial vapor flow is probably produced from the contact point instead, leading to a higher heat flux to the liquid.

Investigation on the difference of geyser behaviors among different cryogenic fuels of launch vehicle

The safety issues of geyser instability in cryogenic fuels have imposed a restriction on their utilization and development. In order to get a comprehensive knowledge of geyser in different cryogenic fuels, in the present paper, a numerical investigation is conducted to figure out the geyser appearance in liquid hydrogen, liquid oxygen, liquid methane and liquid nitrogen. The geyser behaviors in these cryogens are analyzed and compared in detail. The physics of the reason leading to the differences among different cryogenic fuels is comprehensively explored. Results show that geyser is more likely to occur in LO2 and has the largest intensity due to the strong energy storage ability, and difficult to occur in LH2 pipe, where a stable boiling state with a high gas void fraction might exist instead. It is found that the density difference is the main reason for the distinction among the investigated cryogens. Furthermore, a dimensionless parameter of the maximum energy storage ability (Ae) is proposed to quantitatively estimate the geyser's intensity. And it turns out to have a good prediction ability. Moreover, it is found that the increase of Ae arises the possibility and intensity of geyser occurrence. And if Ae goes over 4, a strong geyser with a harmful pressure peak might occur. The findings could give an in-depth understanding of geyser in different cryogenic fuels and assist the design of cryogenic transportation and storage systems.

Water Electrolysis for Propulsion of a Crewed Mars Mission

NASA’s Mars Design Reference Architecture 5.0 presents architecture options for a crewed Mars mission. This paper compares the cryogenic chemical-propulsion option in that study with an alternative: water-electrolysis propulsion. Propellant is stored as liquid water instead of cryogenic hydrogen and oxygen, and then electrolyzed on demand into gaseous hydrogen and oxygen for combustion. This addresses a technology gap in the reference architecture: cryogenic propellant storage life. Water is inert and stable, allowing indefinite storage. The mission refuels from pre-positioned tanks at a lunar libration point and Mars orbit, significantly reducing vehicle mass. Low-thrust transfers between Earth escape, Mars encounter, and vice versa reduce the need to store gas for impulsive maneuvers. Only relatively small impulsive maneuvers are used for orbit injection, escape, and plane changes. The proposed architecture achieves the same mission with at most the same number of launch vehicles and without cryogenic propellant storage. Both architectures use five superheavy lift launch vehicles; however, the reference architecture demands all five within 120 days. The alternative is more flexible. Pre-positioning propellant ahead of time allows a less demanding launch cadence. Potential utilization of water from the moon or elsewhere reduces the number of launches from five to as few as two.

Calculation of Energy Parameters of LNG Power Plant with Utilization its Cold Energy

This paper proposes the possibility of using a cryogenic power plant as part of a hybrid engine, which can be used in the system of urban transport infrastructure. The model of this cryogenic power plant consists of main contour and auxiliary contour of power plants. The parameters of a hybrid cryogenic power plant were evaluated and the characteristics of the main contour of a hybrid power plant driven by a piston expander and a turbo expander with heat input from both the ambient and the exhaust gases of a diesel engine were calculated. Liquid methane is used as the main fuel. The optimal operation cycle of the auxiliary contour of power plant itself has been determined. For this purpose the main parameters of Rankin and Brayton cycles have been analyzed - consumption, power, efficiency. Besides, the most suitable cryogenic fuels for efficient operation were determined and the schemes of the plants were proposed. The calculations were performed using calculation algorithms, examples of which are presented in this article.

The Impact of Solution Treatment Time (T6) and Deep Cryogenic Treatment on the Microstructure and Wear Performance of Magnesium Alloy AZ91

In this study, the AZ91 magnesium alloy was subjected to solution and ageing heat treatment (T6) and deep cryogenic (DC) treatment to enhance the wear performance. For this purpose, the solution treatment process was performed at 400 °C for 4 h, 5 h, and 6 h, followed by ageing at 200 °C for 10 h to complete T6 treatment. Then, the DC treatment was carried out at − 196 °C for 48 h. The pin-on-disc method was employed to measure the wear resistance of the samples. The results show that the solution treatment period altered the microstructure of AZ91; the eutectic phase was more dissolved in the matrix after 4 h of solution treatment time. Regarding the DC-treated AZ91, new double twins frame-like β phases were observed on the surface. Moreover, cryogenic treatment improved the hardness from 63 to 75 HV, but the wear rate was slightly higher than untreated AZ91 in dry medium. On the other hand, lower wear rate was obtained when applying 4 h of solution treatment time with DC treatment. In contrast, 6 h of solution treatment time with DC treatment exhibited higher wear rate, probably due to greater amounts of double twins.

Parahydrogen–Orthohydrogen Conversion on Catalyst-Loaded Scrim for Vapor-Cooled Shielding of Cryogenic Storage Vessels

As long-distance human space travel becomes more realistic, the need for long-term storage of cryogenic propellants becomes a forefront issue. Effective cryo-fluid system management becomes a necessity to solve this issue. The fuel–oxidizer combination of choice for NASA’s Space Launch System is liquid hydrogen () and liquid oxygen (LOX). The current strategy used on many upper stage vehicles, including United Launch Alliance’s Advanced Cryogenic Evolved Stage, is to use the boil-off gases of the colder cryogen () to help insulate the warmer cryogen (LOX) and reduce the static boil-off. In this work, experimental measurements are collected for a range of catalyst materials and weight loadings of and catalysts on Nomex scrim blankets. The blankets are configured in a nonisothermal catalytic reactor with a 23 K input temperature and heated to 90 K output temperature. Results of catalyzation of parahydrogen to orthohydrogen gas are presented as well as a catalyzation model to represent the measurements for future use. In addition, simplified computational fluid dynamics studies have been initiated to estimate the surface-based conversion rate constant by matching numerical results and experimental data.

Thermal physical process in a liquid oxygen tank under different sloshing excitations

Fluid sloshing usually results in some unpredictable effects, including additional sloshing force and moment, and thermodynamic imbalances. It is necessary to conduct in-depth investigations on fluid sloshing to ensure the safe storage of cryogenic propellants. From our own perspectives, the thermal physical performance during sloshing in cryogenic storage tanks is often ignored and few reported. In this study, a numerical model is built to study the coupling thermal physical and fluid sloshing process with the volume of fluid method adopted. Both the external heat invasion and interfacial phase change are considered to predict the thermal performance during fluid sloshing. With the sloshing excitation realized by the user-defined function, the effect of the excitation type on fluid sloshing, has been studied. The results show the sloshing excitations have great influences on the thermal physical process in cryogenic storage tanks. With some valuable conclusions achieved, the present study is significant to depth understanding fluid sloshing thermal behavior.

Primary breakup regimes for cryogenic flash atomization

Flash boiling atomization can occur in rocket thrusters operating in the vacuum of space when the cryogenic liquid propellants are injected into the reaction chamber just before ignition. The sudden drop in pressure triggers the nucleation of microscopic vapour bubbles that grow in the superheated liquid, leading to extreme jet expansion and atomization. Direct numerical simulations are performed using the multiphase solver FS3D to bring insight into the primary atomization process occurring at the microscopic level. The code uses the volume of fluid method and PLIC reconstruction to track the liquid-vapour interface with high fidelity, fully resolving viscous and capillary effects. An incompressible scheme is used, yet all the relevant thermodynamic effects associated with flash boiling are considered by calibration of the evaporation rate and fluid properties based on exact solutions for bubble growth in superheat liquid. A series of test cases with regular bubble arrays demonstrates how the initial bubble spacing and liquid temperature can be correlated to a range of Weber and Ohnesorge numbers. This allows for the definition of very distinct breakup mechanisms and resulting droplet patterns. These extend beyond the common assumptions used in the literature to estimate the primary droplet size and indicate a range of possible droplet size distributions dependening on the breakup regime.

Thermodynamic model of cryogenic fuel tank processes

A new procedure is created for the calculation of heat and mass transfer processes in a cryogenic rocket tank. This simplified method is based on the assumption about homogeneity of temperature in liquid and vapor phase of a fuel component. This assumption made this model useful for such regime as refueling, self-pressurization, pressurization during engine working and other. As the example of method applicability, some calculation is made for refueling of KVTK upper stage to estimate component losses. For the self-pressurization regime, the results of the calculation is compared with experimental data for one cylindrical and one spherical hydrogen tanks. This comparison is shown that pressure rise rate in a full tank several times upper than in the calculations. But for the low level of liquid hydrogen the accuracy of this method is significantly increased. As the result, this procedure is recommended as a lover score of pressure rise during self-pressurization. Key words: cryogenic propellant tank, cryogenic fuel storage, cryogenic tank processes, mathematical modelling, calculation method, refueling, mass-average temperature.

Numerical and experimental analysis of flashing cryogenic nitrogen

The development of new upper orbit thrusters using cryogenic propellants requires an improved understanding of the dynamics of oxidizer and fuel injection at near vacuum conditions before ignition. Due to the low ambient pressure, the propellants enter a superheated state and flash evaporation occurs. Flash boiling of cryogenic liquid nitrogen is studied experimentally on the newly developed test bench at DLR Lampoldshausen and numerically with a newly developed OpenFOAM© solver. Here, a one-fluid approach is selected where phase properties, such as density, enthalpy and saturation conditions are determined with the thermodynamic library CoolProp and tabulated before runtime. The phase change is modeled by the homogeneous relaxation model. For highly superheated jets the flow becomes supersonic and forms a shock after the injector outlet. The solver is validated with the aid of flashing acetone spray experiments where the shock structures are more clearly visible. The results show that the developed solver is capable to predict the all important gas dynamics by matching shock structure and spray angle to the experiment. The experiments using cryogenic liquid, however, do not reveal any shock structures but regions with low negative axial velocities can be identified on the jet centerline. A comparison with the simulations now demonstrates that shocks continue to persist but the respective shadowgraph signals may be obscured in these flows. The joint experimental and numerical study thus provides a consistent understanding of the observed flow features that govern the fluid dynamics and jet breakup of cryogenic flashing flows.

Numerical analysis of spray characteristics with liquid nitrogen

Spray of cryogenic fluids, which involves complicated aerodynamic instability and superheat flashing, is receiving increasing attention in cryogenic cooling applications and cryogenic propellant ignition. In the present study, a two-fluid numerical model coupling the Algebraic Interfacial Area Density (AIAD) model and Homogeneous Relaxation Model (HRM) framework was built to investigate the underlying physics of liquid nitrogen (LN2) spray. The proposed approach aims at describing the underlying physics affected by both aerodynamic and flashing dynamics. Behaviors of spray characteristics, including flow regime, pressure distribution, velocity distribution and intact core length, are analyzed subsequently. Accordingly, effects of aerodynamic instability and flashing on the LN2 spray were analyzed. Finally, a modified correlation of liquid-intact-core length which involves both of the aerodynamic and thermodynamic effects was proposed and the weight of two effects were evaluated accordingly.

Performance Assessment of Ultrasonic Waves for Bubble Control in Cryogenic Fuel Tanks

An efficient long-term storage of cryogenic propellants is a challenge for future space exploration missions. The vapour bubbles formed as a result of boil-off in the tank walls can generate foam structures, which could be hazardous in different operations in orbit. A recently proposed approach to control the dynamics of bubbles is based on the generation of an acoustic field by means of a piezoelectric transducer. This technology needs to be validated at cryogenic temperatures in order to be applicable in space. In this perspective, different piezoelectric elements and matching layer materials have been tested at cryogenic temperatures to assess their performance at such environmental conditions. We consider the use of soft PZT piezoceramics coupled with an epoxy resin as the matching layer. Experimental data reveal that epoxy resin-based acoustic matching layers exhibit a linear increase in the transmittance of the acoustic amplitude at cryogenic conditions. The peak-to-peak amplitude increases as temperature decreases up to a factor of 1.6. This result opens the possibility of generating and transmitting acoustic waves at cryogenic temperatures, which could be used in the recently proposed technology to control the dynamics of vapour bubbles in cryogenic fuel tanks.

Liquid hydrogen line chilldown experiments at high Reynolds numbers. II. Analysis

This paper presents in-depth analysis of the recently conducted high Reynolds (Re) number liquid hydrogen (LH2) transfer line chilldown experiments at NASA Glenn Research Center. Vertically upward trickle and pulse flow chilldown tests were conducted over a wide range of LH2 liquid temperatures (20.3 K – 24.2 K) and mass flow rates (0.0012 – 0.036 kg/s) typical of a proposed cryogenic propellant depot. Two-phase flow mapping is used to correlate flow visualization with LH2 stream temperature profiles. Thermodynamic state diagrams, reverse boiling curves, and heat transfer coefficients are used to explain the evolution of the chill down process at various locations. Analysis reveals stark differences in behavior between skin and stream temperature measurements due to annular flow and bubbly flow dominated cooling. Analysis also shows that hydrogen chilldown at high Re numbers promotes better mixing and thus more liquid contact along the wall earlier on, in comparison to chilldown with other fluids like nitrogen where classical inverted annular flow boiling is incurred.

Development of Damping Support for a Turbine Pump Assembly of a Cryogenic Fuel Aviation Gas Turbine Engine

Theoretical studies and design studies have been conducted to demonstrate the possibility of using a long hydrodynamic damper in the supports of a hydrogen pump rotor was shown. The complex problem of rotor dynamics and design synthesis of a hydrodynamic damper for a turbopump assembly (TPA) was solved. The geometric parameters of the hydrodynamic damper are determined that ensure the necessary damping level, d = 3 × 103 N s/m. It is shown that at such a damping level, the amplitude of rotor oscillations does not exceed the value of clearances in supports and on blade shoulders.

Numerical analysis of the flow dynamics of an N2 cryogenic jet

Injection and mixing of cryogenic propellants are very complex at near-critical and supercritical conditions. The concise description and the reliable measurements on such flows are still questionable. In this work, a RANS study is performed for a pure N2 fluid injection at transcritical conditions on a laboratory scale test rig. An in-depth thermodynamical analysis on the real-gas behavior has allowed N2 density prediction over the experimental range of the injection temperature and for several equations of state. A focus was thrown on the prediction of the density evolution on the chamber centerline and across the injector. The calculations were performed using both adiabatic and constant temperature conditions for the injector wall. The inner heat transfer in the injector had a significant effect on the jet density distribution and therefore, on the overall flow dynamics. Numerical results regarding axial profiles of density and dense core lengths agree fairly well with the experimental data provided by the literature.

Numerical investigation on hydrodynamic characteristics of two-phase flow with liquid hydrogen through cryogenic feed lines at terrestrial and microgravity

Two-phase flow of cryogenic propellants in feed lines during the chill-down operation for space application system is inevitable. Such cooling process exhibits dynamic response, which are difficult to control due to flow instabilities and differential cooling rates. Moreover, the dynamics of two-phase phenomena in microgravity differ from that operated at terrestrial gravity. Hence, in the present work, transient modelling for two-phase flow of liquid hydrogen (LH2) is presented. A 3-dimensional computational model of a cryogenic feed line have been developed and meshed using commercial software ICEM CFD and exported to the solver ANSYS-FLUENT. Volume of Fluid (VOF) method based on Eulerian flow scheme is implemented in order to capture the two-phase flow of LH2 and for reliable prediction of hydrodynamic characteristics at various gravity conditions. Void fractions at different locations of the vertical pipe are obtained and Probability Density Functions (PDFs) are generated in order to predict the morphology of the flow regime. Moreover, velocity profiles along with phase distribution are presented to analyze the interfacial behaviour and reveal the structure of two-phase flow. Annular dominant slug flow is obtained in the present work, whereas bubbly dominant slug flow was obtained in the reference work for conventional fluids (air-silicone mixture). Moreover, PDF signatures reveal that the probability of occurrence of annular characteristic is ~1.3 and 3.5 times to that of bubbly feature at terrestrial and microgravity conditions respectively. Hence, the present methodology is useful in the prediction of flow structure and phase distribution at terrestrial and microgravity conditions.