Injection Mode Research Articles

Effects of second hydrogen direct injection proportion and injection timing on combustion and emission characteristics of hydrogen/n-butanol combined injection engine

Hydrogen and n-butanol are superior alternative fuels for SI engines, which show high potential in improving the combustion and emission characteristics of internal combustion engines. However, both still have disadvantages when applied individually. N-butanol fuel has poor evaporative atomization properties and high latent heat of vaporization. Burning n-butanol fuel alone can lead to incomplete combustion and lower temperature in the cylinder. Hydrogen is not easily stored and transported, and the engine is prone to backfire or detonation only using hydrogen. Therefore, this paper investigates the effects of hydrogen direct injection strategies on the combustion and emission characteristics of n-butanol/hydrogen dual-fuel engines based on n-butanol port injection/split hydrogen direct injection mode and the synergistic optimization of their characteristics. The energy of hydrogen is 20% of the total energy of the fuel in the cylinder. The experimental results show that a balance between dynamics and emission characteristics can be found using split hydrogen direct injection. Compared with the second hydrogen injection proportion (IP2) = 0, the split hydrogen direct injection can promote the formation of a stable flame kernel, shorten the flame development period and rapid combustion period, and reduce the cyclic variation. When the IP2 is 25%, 50% and 75%, the engine torque increases by 0.14%, 1.50% and 3.00% and the maximum in-cylinder pressure increases by 1.9%, 2.3% and 0.6% respectively. Compared with IP2 = 100%, HC emissions are reduced by 7.8%, 15.4% and 24.7% and NOx emissions are reduced by 16.4%, 13.8% and 7.9% respectively, when the IP2 is 25%, 50% and 75%. As second hydrogen injection timing (IT2) is advanced, CA0-10 and CA10-90 show a decreasing and then increasing trend. The maximum in-cylinder pressure rises and falls, and the engine torque gradually decreases. The CO emissions show a trend of decreasing and remaining constant. However, the trends of HC emissions and NOx emissions with IT2 are not consistent at different IP2. Considering the engine's dynamics and emission characteristics, the first hydrogen injection proportion (IP1) = 25% plus first hydrogen injection timing (IT1) = 240°CA BTDC combined with IP2 = 75% plus IT2 = 105°CA BTDC is the superior split hydrogen direct injection strategy.

Investigation on water-drive performance of a fault-karst carbonate reservoir under different well patterns and injection-production modes based on 2D visualized physical models

Recently, a new type of carbonate reservoir, the fault-karst carbonate reservoir has attracted lots of attention, which usually develops large-scale karst caves, vugs, and high-angle fractures along the strike-slip fault zones. Despite containing plenty of hydrocarbon resources, the complex geological structure and the strong heterogeneity make it difficult to develop this kind of reservoir effectively and economically. To perform water-drive experiments and investigate the production performance under different well patterns and injection-production modes, two 2D visualized physical models were designed and fabricated based on the typical geological structures of the fault-karst carbonate reservoir in the vertical and horizontal directions, respectively. According to the experimental results, the average oil recovery can reach 62.96% for the vertical model and 58.18% for the horizontal model. In fact, gravity effect due to density differences can greatly improve the displacement efficiency of oil by water in the vertical direction; hence, the horizontal heterogeneity would have a relatively greater impact on waterflooding development. When water is injected into the reservoir from the middle section, a large amount of un-swept oil will remain at the bottom fractures. Thus, the Bottom Injection & Top Production (BI & TP) mode should be adopted in all well patterns to increase recovery. If non-inverted well patterns are employed, dominant water channeling would form quickly in the horizontal direction, and the swept area will be hugely limited. Therefore, the Center Injection & Edge Production mode (inverted well patterns) is recommended for water-drive applications. It is also found that the water breakthrough time negatively correlates with the effective flooding time for the vertical model and the total oil recovery is more impacted by water breakthrough for both models. Additionally, the oil-water exchange ratio is introduced to evaluate the utilization efficiency of injected water. Calculation results have shown that the BI & TP mode is optimal in terms of either total recovery or oil-water exchange ratio in the vertical direction, but the well pattern layout in the horizontal direction could impact the oil recovery and oil-water exchange ratio, which, in turn, affect the project economics. This study provides novel insights for optimizing well patterns and waterflooding measures in actual fault-karst carbonate reservoirs.

An SEU fault injection platform for radiation-harden design debugging in the FPGA

An SEU fault injection platform was designed to ease the debugging of radiation-harden design in FPGA. The platform includes the FPGA being tested, the functional firmware being debugged, the essential-bit extraction algorithm based on Python, and the random fault injection algorithm. The platform can inject single-bit SEU failures, adjacent two-bit SEU failures, and three-bit SEU failures. It works in two modes: normal injection mode and essential-bit injection mode. Functional failure rate is the performance metric which used to evaluate the development. It is the probability of triggering a DUT function failure. In this experiment, the SEU fault injection platform is verified by measuring whether TCP/IP communication links are disconnected due to SEU faults. Experimental results show that the probability of TCP/IP link disconnection in normal injection mode is 0.13%, 0.23% and 0.25% respectively when random injection of single-bit SEU failure, adjacent two-bit SEU failure and multi-bit SEU failure occurs 10,000 times. In the essential-bit injection mode, the probability of TCP/IP link disconnection caused by single-bit SEUs failure, adjacent two-bit SEUs failure and three-bit SEUs failure is 0.87%, 6.97% and 11.76% respectively, indicating a significant increase in the functional failure rates. This shows that the essential-bit injection mode can be used to expose problems more quickly and accelerate the debugging process of FPGA radiation-harden design.

Five-Phase Hybrid Single-/Double-Layer Fractional Slot-Winding PMSM for Torque Improvement Under Third Harmonic Current Injection Condition

A 60-slot/22-pole five-phase machine with hybrid single-/double-layer fractional slot winding is proposed to improve torque under third harmonic current injection condition. Design process of the proposed machine includes two steps of first combining two sets of 20-slot/22-pole machine windings and then shortening coil-pitch. Due to the special structure of the proposed machine, torque-contributing space harmonics in magnetomotive force (MMF) are improved, and redundant space harmonic in MMF which causes high eddy current loss in permanent magnets is suppressed. The proposed machine is evaluated under two modes of third harmonic current injection, namely constant rms and peak harmonic injection. Compared with 20-slot/22-pole machine, the proposed machine achieves higher torque and lower losses under both third harmonic current injection conditions. Besides, the performance of the proposed machine when injecting only the first or third harmonic current is also analyzed.

Enhanced Carrier Confinement and Mode Discrimination for Laterally-Coupled DFB Lasers

Reducing carrier leakage is the key to obtain laterally coupled distributed feedback (DFB) lasers with high injection efficiency. We proposed a device structure with slots fabricated between the ridge and gratings to form a good confinement on carriers. The incorporation of slots also makes the grating morphology easier to fabricate. To evaluate the dependence of coupling efficient on main structural parameters, four grating samples with different sizes are studied with FDTD Solutions. Calculation results indicate that slots with a width of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.1\!-\!0.3\;\mu{m}$</tex-math></inline-formula> is suitable for the device. And, changing the lateral width of the grating can be used as a direct method to adjust the coupling strength. In addition, the carrier distribution and optical field distribution of the device were simulated with Crosslight PICS3D, and the results show that compared with the traditional laterally-coupled gratings, this structure can strengthen the competitive advantage of fundamental mode and enhance the mode discrimination of the device. This structural design provides ideas and references for improving the injection efficiency and mode stability of laterally-coupled DFB lasers.

Theoretical Study of LED Operating in Noncarrier Injection Mode.

Non-carrier injection (NCI) mode is an emerging driving mode for light-emitting diodes (LEDs) with numerous advantages. Revealing the relationship between the current and the applied alternating voltage in mathematical formulas is of great significance for understanding the working mechanism of NCI–LEDs and improving device performance. In this work, a theoretical model of the relationship between NCI–LED current and time-varying voltage is constructed. Based on the theoretical model, the real-time current is derived, which is consistent with the experimental results. Key parameters that can improve device performance are discussed, including voltage amplitude, frequency, equivalent capacitance, and LED reverse current. The theory presented here can serve as an important guidance for the rational design of the NCI–LEDs.

"Bi-Bi" technique for lip augmentation: A retrospective study on 30 cases.

Lip augmentation is achieved mainly by using hyaluronic acid (HA) fillers. The injection procedures are performed either superficially or deeply with a needle or a cannula, and only one type of hyaluronic acid is used. The authors' objective was to evaluate the feasibility, safety, and satisfaction level of a procedure combining two anatomical injection plans, two injection modes (i.e., cannula and needle), and two types of hyaluronic acid fillers. The retrospective study included 30 patients who underwent the following procedure: Intramuscular retro-trace injections of Stylage M (Vivacy® Laboratories) were conducted through a 27-gauge cannula at the level of the upper and lower hemi-lip. Then, intradermal injections of Stylage Lips (Vivacy® Laboratories) using a 33-gauge needle were carried out on the entire lip border as well as the cupid's bow. During a post-injection follow-up, subjects were asked to evaluate satisfaction level and the effect of fillers over time. Elastic (G') and viscosity (G″) moduli of HA fillers were measured with a rheometer (AR2000, TA Instruments) prior to and after extrusion through a 33-gauge needle. Rheological assessment showed that passage through a 33-gauge needle did not alter the viscoelastic properties of HA fillers. After the clinical procedure, no side effects were observed except for standard post-treatment bruises and edema. No vascular incident occurred. Moreover, overall patient satisfaction was high (2.6/3) and there was a long-lasting perception of the effect of the filler. The current study demonstrated that dissociating the anatomical zones of the lip during the injection procedure by means of different hyaluronic acids in the muscular and dermal planes would efficiently and safely provide both lip projection and fullness for a natural and lasting effect.

Screening of local hyaluronic acid injection modes to increase the efficiency of treating crush injury of soft tissues

Aim. To study the state of microcirculation and metabolic activity of the soft tissues in the compression area in experimental crush injury after local hyaluronic acid injection and to determine the effective mode of its application.Materials and methods. The experiments were carried out on 178 male Wistar rats aged 4–4.5 months and weighing 280–340 g. The study design included anesthesia, modeling of crush injury (CI), local injection of 1.75% hyaluronic acid (HA) solution into the compression area, systemic intravenous injection of 0.9% sodium chloride solution daily for 3 days, and a study of microcirculation and metabolism of the soft tissues in the damaged area 3, 7, 14, and 28 days after the injury.Results. Early (3 hours after the injury) local application of HA for CI improved microcirculation, increased oxygen consumption, and activated oxidative metabolism in the skeletal muscles, which helped reduce the severity of destructive processes in the damaged area. The most effective injection mode was two-fold administration of HA: 3 hours after the compression cessation and additionally 24 hours after the injury.Conclusion. In the crush injury, early local intramuscular injection of HA into the damaged area in the first few hours after the cessation of compression is a sanogenetically substantiated method for correcting traumatic ischemia of the muscles.

Effects of direct injection and mixture enleament on the combustion of hydrous ethanol and an ethanol-gasoline blend in an optical engine

Ethanol is a renewable fuel and can be used in electric hybrid vehicles concepts, especially for countries capable of producing such fuel in a sustainable way. A strategy to enhance these concepts is the use of lean-burn combustion, which is an effective way to improve the fuel economy from spark-ignition engines, while obtaining low pollutant emissions. However, these improvements are complicated to achieve in a practical way because lean combustion has low rates of reaction, extinction, and misfire cycles, leading to cyclical variability for the engine operation. The drawback becomes even greater when lean combustion is associated with commercial ethanol fuels and direct injection. Therefore, the objective of the present work is to provide an experimental analysis of spray guided direct injection with commercial fuels used in a consolidated market for the use of ethanol such as the Brazilian one, in particular hydrous ethanol (E95W05) and ethanol-gasoline blends (E27G73). The experiments were conducted in an optically accessible spark-ignition engine and the lean combustion effects on engine cycle variability, performance, flame morphology, and exhaust emissions were assessed. In general, the results indicated that combustion instabilities can be correlated from thermodynamic and optical analyses. Flame instabilities for E95W05 were associated with the lower flame propagation speed caused by the temperature reduction during lean combustion. Additionally, exhaust emissions contained the presence of unburned ethanol which increased when combustion became leaner. Moreover, the lower flame propagation speed was one of the factors responsible for reducing engine performance and increasing combustion variability. The results indicated that vaporization was a relevant phenomenon affecting ethanol combustion in the direct injection mode. The cooling effect of fuel vaporization presented itself as a powerful means for the reduction of NOx and aldehydes, even for the lean operation. Higher emissions of CO and THC were also observed for the engine operating with E95W05 when compared to E27G73. The results of the present work showed that special attention must be paid to the use of commercial fuel with a high ethanol content in spray-guided direct injection engines, especially during lean-burn combustion, in order to not compromise the performance nor increase pollutant emissions.

Characteristics of water alternating CO2 injection in low-permeability beach-bar sand reservoirs

Water flooding can be ineffective in highly heterogeneous low-permeability beach-bar sand reservoirs. The introduction of CO2 flooding helps boost the oil production of the reservoirs but only in an early stage. During the late stage of flooding, gas channeling would occur. Water alternating gas (CO2) (WAG) process can be used to delay gas channeling and improve the effect of CO2 injection, though its adaptability to beach-bar sand reservoirs remains unclear. In order to clarify CO2 injection characteristics in these reservoirs, experiments were carried out in high-temperature high-pressure NMR on-line displacement experiment apparatus to simulate different flooding modes on synthetic cores that can reflect the vertical heterogeneity of beach-bar reservoirs. Different CO2 injection modes were implemented on these cores and the displacement characteristics and residual oil distribution features during both WAG injection and continuous CO2 injection were analyzed quantitatively and qualitatively. The results show that the scheme of WAG injection after continuous CO2 injection can obtain better oil displacement efficiency than that of the scheme of continuous CO2 injection after WAG injection, but there is no significant difference in respect of oil displacement efficiency of WAG flooding between the mode of bar-injection – beach-production (injection into bar sand – production from beach sand) and the mode of beach-injection – beach-production (injection into and production from beach sand), with the former mode having a higher oil recovery rate. The wider pore-size distribution range of microscopic residual oil after WAG injection shows great potential of enhancing oil recovery from subsequent continuous gas injection. When WAG injection is implemented prior to continuous CO2 injection, the displacement effect of the latter is more significant. This research may provide a theoretical basis for CO2 EOR in this type of reservoirs.

Ultralow-voltage operation of light-emitting diodes

For a light-emitting diode (LED) to generate light, the minimum voltage required is widely considered to be the emitter’s bandgap divided by the elementary charge. Here we show for many classes of LEDs, including those based on perovskite, organic, quantum-dot and III–V semiconductors, light emission can be observed at record-low voltages of 36–60% of their bandgaps, exhibiting a large apparent energy gain of 0.6–1.4 eV per photon. For 17 types of LEDs with different modes of charge injection and recombination (dark saturation currents of ~10−39–10−15 mA cm−2), their emission intensity-voltage curves under low voltages show similar behaviours. These observations and their consistency with the diode simulations suggest the ultralow-voltage electroluminescence arises from a universal origin—the radiative recombination of non-thermal-equilibrium band-edge carriers whose populations are determined by the Fermi-Dirac function perturbed by a small external bias. These results indicate the potential of low-voltage LEDs for communications, computational and energy applications.

Hydraulic Issues Concerning Injection of Harvested Rainwater to the Subsurface Through Drywells: Insight From Numerical Simulations of Flow in a Realistic Combined Vadose Zone‐Groundwater Flow System

AbstractThis study focuses on the analyses of field‐scale water flow originating from a drywell, using the 3‐D Richards equation for the local description of the flow in a spatially heterogeneous, combined vadose zone‐groundwater flow system. Realistic features of the flow system, that is, height of the groundwater table, records of the time‐dependent rainfall data, spatial heterogeneity of soil hydraulic properties and flow‐controlled attributes, as well as man‐controlled characteristics of the drywell, were considered in the analyses. The effect of (a) the depth‐dependency of the soil type, (b) the vertical position of the drywell's screen, and (c) the mode of water injection to the drywell (constant or time‐dependent), on the performance of the drywell, were examined. Results, and in particular those related to the importance of the soil type depth‐dependency with regard to the drywell performance, can be explained by the physics of flow in unsaturated soils of differing soil texture. Of specific significance is the transition zone between the two different soil types in the case in which the spatially‐heterogeneous coarse‐textured soil overlies the spatially heterogeneous fine‐textured soil. In this case, when most of the drywell screen is located within this transition zone and when the flow is transient and non‐monotonous, the downward flow from the drywell is maximized. Although this study is site‐specific, we believe that its results are novel and relevant for sandy to sandy‐clay soils associated with managed aquifer recharge technology based on a device whose vertical axis is perpendicular to the soil layering.

Investigation of enhanced exploitation of natural gas hydrate and CO2 sequestration combined gradual heat stimulation with CO2 replacement in sediments

CO2 replacement is a promising technology that simultaneously produces methane and carbon dioxide sequestration. In this work, a novel gradual heat injection enhanced replacement method (GHIR) was proposed to improve the methane production from natural gas hydrate sedimentary layer. The effects of heat injection mode on methane recovery, energy efficiency and the optimal operating conditions of GHIR were studied. The results have shown that GHIR enhances the CH4 recovery percentage from 8.0% to 25.4%. EROI could be further enhanced to 20.14. Because the thermal conductivity of hydrate is larger than the dissociation hydrate layer, the heat transfer analysis shown that the incremental heat injection enhanced replacement method (IHIR) is the best mode for gradual heat stimulation combined CO2 replacement. This work provides a novel method for future marine NGH development and promotes carbon sequestration by applying the CH4/CO2 replacement method.

Comparison of ethanol/diesel fuel dual direct injection (DI2) strategy with reactivity controlled compression ignition (RCCI) in a diesel research engine

The dual direct injection (DI2) strategy is expected to cover the advantages of conventional diesel (CDI) mode while avoiding deficiencies of reactivity controlled compression ignition (RCCI) strategy such as high amount of incomplete combustion emissions and extremely high rate of pressure rise. Therefore, the present study focused on the comparison of combustion characteristics of these combustion modes in a diesel research engine, which was firstly operated under CDI mode at varying loadings and a constant speed of 2400 rpm to establish the reference data. Then, a low pressure port fuel injection (PFI) and high pressure gasoline direct injection (GDI) systems were activated to run on RCCI and DI2 modes, respectively, whereas test engine was already equipped with a common-rail direct injection (CRDI) system for conventional diesel fuel injection. Results showed that both direct and port injection methods increased the in-cylinder pressure (up to 9%) compared to conventional mode. In RCCI combustion, the rate of pressure rise increased more than direct injection and conventional mode. CDI exhibited higher thermal efficiency than RCCI and DI2 modes while both advanced modes were successful in reducing NOx and Smoke Opacity. However, significantly higher CO and unburned HC emissions were observed with both advanced modes in comparison to conventional one. Both CO and unburned HC emissions were reduced by direct injection of ethanol (DI2 strategy) at the rates of 16% and 35% compared with port injection method of RCCI strategy. This is an important finding of this study, which shows that the DI2 strategy has a potential to address a deficiency of RCCI and will bring it closer to its application to practical engines.

Precision improvement of patch potential measurement in a scanning probe equipped torsion pendulum

Patch effect is important for ultra-sensitive experiments involving closely spaced conducting surfaces. A scanning probe equipped torsion pendulum is an experimental apparatus for measuring spatial resolved patch potential on conductive surfaces. An effective approach to improve its measurement precision is by the optimization on the amplitude and frequency of the injected signal in the probe. In this paper, a method based on single- and double-frequency signal injection modes is proposed. The analysis results demonstrate that the potential resolution could achieve the level of 2-4 μV/Hz1/2. In the same integration time, the surface potential precision in the double-frequency mode is twice better than that in the single-frequency mode. In addition, when achieving the same measurement precision, the double-frequency mode takes less time than the single-frequency mode, which improves the measuring efficiency.

Abrasive Jet Perforating Restores Productivity of an Inactive Oil Producer

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208988, “Novel Application of Abrasive Jet Perforating To Restore Productivity of a High-Potential Inactive Horizontal Oil Producer,” by Sadaf S. Chishti, SPE, Steven H. Craig, SPE, Baker Hughes, and Edward J. Wheatley, SPE, ADNOC, et al. The paper has not been peer reviewed. The complete paper illustrates a novel methodology that enabled the safe application of coiled tubing (CT) abrasive perforation to increase production in a sour horizontal extended-reach (ER) oil producer. The well was underperforming at 10% of the anticipated production rate because of a damaged lower completion. To avert a costly workover, abrasive perforation with CT was selected as a safe alternative to conventional explosives-based perforating conveyed on electric line. Introduction An offshore horizontal ER producer well was drilled with a total depth (TD) in excess of 24,000-ft measured depth (MD). During the completion phase, a 4.5-in. liner with 16 inflow control devices (ICDs) and eight swellable packers was run with the ICDs in the closed position. Swellable packers were placed after every two ICDs. To open these ICDs, an internal pressure of 2,500 psi was required, achieved by dropping a ball that would seat in the float collar. Multiple attempts were made to pressure up and open the ICDs without success. The decision was made to run the upper completion with a plan to activate the ICDs using rigless CT intervention. After a drift CT run, multiple attempts were made to run a through-tubing inflatable packer bottomhole assembly (BHA) on CT to isolate and pressure up the well. All attempts failed to reach target depth, with repeated holdup at approximately 20,273-ft MD. Production-logging passes performed in injection mode determined that the well interval between 20,262 and 20,300 ft was taking more than 80% of the injected fluid. In a subsequent CT logging run, a caliper log identified that the liner section in this interval was parted and identified an openhole section with washouts in excess of 7-in. inner diameter. The results from the log are shown in Fig. 1, with the enlarged section representing the parted liner/openhole interval. Because the ICDs remained closed along with a damaged liner section, the options of recovery leaned heavily toward a rig-based workover for sidetrack and recompletion. Considering time and cost constraints, studies commenced to identify an efficient alternative to establish flow contribution from the inactive compartments by adding perforations. CT was chosen as the conveyance method based on previous success in reaching TD, and three options were evaluated. Based on the lowest risk level and availability of resources, the safest and most-viable option was abrasive perforation with CT. This technique uses a sand jet perforator, a downhole tool that uses high-pressure abrasive-laden fluids to penetrate the casing, liner, and cement and extend a cavity into the reservoir.

Investigating the effects of injection and induction modes of hydrogen addition in a CRDI pilot diesel-fuel engine with exhaust gas recirculation

This work compares the outcomes of different flow rates of hydrogen added by induction and injection methods in three different flow rates (3, 9, and 15 LPM) through the intake manifold of a constant speed CRDI diesel engine operated at 1500 rpm. The premixed air and hydrogen mixture was ignited by injecting diesel fuel at 23⁰ bTDC. Hydrogen addition reduced CO, HC, and smoke in both the techniques, but efficiency was decreased at a higher percentage of hydrogen induction, whereas it increased with the injection technique. The higher calorific value and flame velocity helped proper combustion and improved brake thermal efficiency by 7%, and the brake-specific energy consumption was reduced by 10.7%. In addition, CO, UHC, and Smoke were decreased by 15.8, 29.7, and 15% compared with neat diesel at full BMEP. Nitrogen oxides decreased by 5.6% for 15 LPM of hydrogen injection compared to the induction method with the same flow rate but higher than diesel fuel by 35.9%. Three different EGR percentages (5, 7.5, and 10%) were used to reduce the higher NOx emission. Though the injection process was complex compared to the induction method, the injection process can provide promising results even at higher hydrogen flow rates.

A Critical Review of Alkaline Flooding: Mechanism, Hybrid Flooding Methods, Laboratory Work, Pilot Projects, and Field Applications

Over time, the dependence on oil has increased to meet industrial and domestic needs. Enhanced oil recovery (EOR) techniques in this regard have captured immense growth as EOR is not only used to increase the oil recovery but also to augment the sweep efficiency. Several techniques over the past decades have been used to improve oil recovery with cost-effectiveness. Cost-effective alkaline flooding has been effective for those oil reservoirs with a high total acid number. In this review, the significance of alkaline flooding has been discussed in detail, as well as the features of alkaline flooding in comparison to other modes of flooding. This review entails (1) alkaline flooding, (2) hybrid modes of injection, (3) experimental work, (4) pilot projects, (5) screening criteria, and (6) field applications. The findings of this study can help increase the understanding of alkaline flooding and provide a holistic view of the hybrid modes of flooding.

Reappraising the Production and Transfer of Hydrogen Atoms From the Middle to the Upper Atmosphere of Mars at Times of Elevated Water Vapor

AbstractWater escape on Mars has recently undergone a paradigm shift with the discovery of unexpected seasonal variations in the population of hydrogen atoms in the exosphere where thermal escape occurs and results in water lost to space. This discovery led to the hypothesis that, contradicting the accepted pathway, atomic hydrogen in the exosphere was not only produced by molecular hydrogen but mostly by high altitude water vapor. Enhanced presence of water at high altitude during southern spring and summer, due to atmospheric warming and intensified transport, favors production of H through photon‐induced ion chemistry of water molecules and thus appears to be the main cause of the observed seasonal variability in escaping hydrogen. This hypothesis is supported by the observation of large concentrations of water vapor between 50 and 150 km during the southern summer solstice and global dust events. Using a simplified yet representative air parcel transport model, we show that in addition to the formation of atomic hydrogen from water photolysis above 80 km, a major fraction of the exospheric hydrogen is formed at altitudes as low as 60 km and is then directly advected to the upper atmosphere. Comparing the injection modes of a variety of events (global dust storm, perihelion periods, and regional storm), we conclude that southern spring/summer controls H production and further ascent into the upper atmosphere on the long term with direct implication for water escape.

Theoretical Study on the Micro-Flow Mechanism of Polymer Flooding in a Double Heterogeneous Oil Layer

Critical issues in the development of oil fields include the differences in the layer properties as well as serious interlayer conflicts and disturbances that can lead to the formation of a preferential flow pathway. In order to understand the interlayer disturbance mechanism between the heterogeneous oil layers, mathematical models of the polymer, and oil two-phase micro-flow in porous media are established based on the Navier-Stokes equation. The phase-field method is used to track the two-phase interface during the displacement process. Then, the influences of wettability, injection modes, and permeability contrasts on the front length coefficient and the displacement efficiency are studied. The results showed that when the rock surface is water-wet (oil-wet), the polymer displaced the low (high) permeability layer first, and the interlayer breakthrough is obvious in the early stages of displacement. After the front broke through, the water-wet (oil-wet) rocks began to displace the high (low) permeability layer, and the preferential flow pathway is formed, which slowed the subsequent polymer flooding. When the rock surface is oil-wet, the perforation degree of the inlet had a greater effect on the micro-oil displacement efficiency. The micro-oil displacement efficiency of the full perforation and commingling production model is 26.21% and 37.75% higher than that of the separate-layer injection and commingling production, as well as the partial perforation and commingling production-injection models, respectively. The larger the permeability contrast, the more obvious the interlayer breakthrough. This study reveals the influence of different wettability characteristics, injection modes, and permeability contrasts on the front length coefficient and the displacement efficiency in a micro-heterogeneous model and provides an important theoretical basis for the formulation of enhanced oil recovery schemes for heterogeneous oil layers.