Nitrogen-enriched Air Research Articles

(Invited) Electrochemical Gas Separation

Electrochemical gas separators are electrically powered systems that selectively remove a targeted gas species from a mixture of gases by virtue of electrochemical reactions. Electrochemical separation is an attractive option owing to its higher efficiency and lower cost compared to incumbent technologies like pressure swing adsorption, cryogenic processes, and selective permeation. This work focuses on two specific electrochemical separation processes – (1) separation of hydrogen from a mixture of gases to help develop the hydrogen distribution infrastructure, and (2) nitrogen separation from air for aircraft fuel tank inerting.Reductions in CO2 emission since the beginning of this century by the US electric power sector are mainly attributed to the replacement of coal by natural gas in power plants. Nevertheless, the combustion of natural gas still contributes heavily to global warming and climate change. It is imperative to find alternatives to combustion-based energy technologies and nurture the growth of renewable energy systems. In this scenario, hydrogen is a leading candidate as a carbon-free fuel with high energy density and is expected to play a key role in future energy systems. However, hydrogen faces serious obstacles in its distribution due to the lack of a nationwide hydrogen pipeline network. Developing a dedicated hydrogen pipeline network will be quite expensive, therefore, it is worthwhile to examine whether existing natural gas pipelines could be effectively deployed for hydrogen distribution. This would be accomplished by directly injecting a prescribed amount of hydrogen at the point of production into a natural gas pipeline. Such a mixture of hydrogen and methane is labeled as hythane. While this enables the convenient transport of hydrogen across large distances, the process can only be completed by separating hydrogen from methane at the destination point. Electrochemical hydrogen separation (ECHS) systems built around proton-selective polymer electrolyte membranes (PEMs) represent an effective platform to separate and simultaneously compress hydrogen in a continuous operation. Furthermore, ECHS ensures that the resulting gas is not contaminated by lubrication oil as observed in conventional systems. In ECHS, the hythane mixture enters the anode compartment wherein the hydrogen is selectively dissociated to protons and electrons. The protons are then driven across the PEM by an externally applied voltage to recover hydrogen at the cathode.The first part of this study demonstrates hydrogen purification using low-temperature PEM-based ECHS from various gas mixtures including methane/hydrogen, carbon dioxide/hydrogen, water gas shift effluent, and hythane. ECHS performance is first investigated for pure hydrogen as a function of membrane thickness, cell temperature, and relative humidity of the anode stream. In the second set of experiments, various ratios of methane/hydrogen and carbon dioxide/hydrogen are introduced to examine the effect of hydrogen concentration in the feed gas mixture on ECHS performance. Finally, experiments are performed for hydrogen purification from a water gas shift (WGS) effluent mixture as well as a practical hythane gas feed. ECHS performance for all gas mixtures was benchmarked against the pure hydrogen case. The purity of the separated hydrogen gas was measured to confirm the effectiveness of the method. The results show that ECHS represents a good solution to separate hydrogen from the hythane mixture at the downstream end of the pipeline.Pertinent to the second electrochemical separation process examined here, after the TWA flight 800 disaster due to a fuel tank explosion in 1996, inerting of aircraft fuel tanks became a priority. During fuel tank inerting, an inert gas like nitrogen is supplied to the tank to reduce its flammability. An electrochemical gas separation and inerting system (EGSIS) is a device that generates nitrogen enriched air (NEA) from ambient air by the application of electrical power. EGSIS combines a PEM electrolyzer anode wherein water is dissociated to release oxygen, and a PEM fuel cell cathode where atmospheric air is converted to NEA. Aircraft tank inerting requires varying NEA flowrates (low during takeoff and ascent, and high during descent). In conventional hollow fiber membrane air separation modules typically used in current aircraft, the total membrane surface area is determined by the maximum required NEA flow rate which results in large and expensive modules. On the other hand, the NEA flow rate can be easily controlled in EGSIS by simply adjusting the applied voltage. This portion of the study focuses on results for a single EGSIS cell and its optimization. Various EGSIS stack configurations are also described in order to develop a practical system. Finally, a techno-economic analysis of EGSIS is presented to show that EGSIS can compete favorably with incumbent technologies in terms of fuel usage and cost.

Electrochemical Air Separation and Emergency Power Fuel Cell for Aircraft

The crash of TWA Flight 800 in July 1996 was attributed to an explosion in the center fuel tank. Since then, commercial airliners have been equipped with inerting systems to prevent explosive mixtures of air and kerosene vapor from forming in fuel tanks. The incumbent technology is based on hollow-fiber membrane (HFM) separation modules that split air into an oxygen-enriched air (OEA) stream and a nitrogen- enriched air (NEA) stream. The nitrogen enriched air used to inert kerosene contains less than 12% oxygen. Other methods for separating air like cryogenic distillation and pressure swing absorption producer purer oxygen than HFM, but they do not scale down well. Another alternative is electrochemical air separation. High-temperature air separation units using solid oxide cells have been investigated for large-scale applications like oxy-combustion to facilitate carbon dioxide sequestration. However, high-temperature technologies may be less suitable for transportation applications. Electrochemical air separation at low temperatures can be accomplished with relatively compact polymer-electrolyte cells that evolve oxygen at the anode and reduce oxygen at the cathode. The effluent from the cathode is nitrogen enriched. This presentation discusses proof of concept tests and uses these to explore the relative merits of this approach versus incumbent HFM. The electrochemical air separation stack can be fed hydrogen to provide power during emergencies, potentially performing the functions of two components on commercial aircraft.

Optimization of an Electrochemical Gas Separation and Inerting System

Aircraft fuel tank inerting is typically accomplished by supplying nitrogen enriched air (NEA) into the ullage (volume of air above the fuel level in the tank). We have developed a novel on-board electrochemical gas separation and inerting system (EGSIS) to generate NEA for fuel tank inerting. EGSIS is an electrically powered system that functionally combines a proton exchange membrane (PEM) fuel cell cathode with an electrolyzer anode. Water management is important in such a PEM-based system because proton transfer requires proper hydration of the membrane. Extremes of both dryout and flooding conditions should be avoided for optimal EGSIS performance. Previous single-cell EGSIS experiments revealed that supplying liquid water at the anode will maintain sufficient membrane hydration even when the system is operated under dry cathode conditions. However, it was difficult to avoid flooding at low cathode air stoichiometries when parallel flow field channels were employed. Here, we implement various strategies to optimize EGSIS performance such as using serpentine and interdigitated flow field channels, as well as a double-layer gas diffusion layer with graded hydrophobicity to mitigate flooding and improve water management. We also present a theoretical analysis of various stack configurations for a practical EGSIS module.

3D Computational Model for an Electrochemical Gas Separation and Inerting System

Aircraft fuel tank inerting is employed to reduce the flammability of the fuel vapor in the ullage (air volume above the fuel) by restricting its oxygen concentration to a safe value—12% for commercial aircraft and 9% for military aircraft. Inerting is typically accomplished by displacing oxygen in the ullage with an inert gas like nitrogen. Electrochemical gas separation and inerting system (EGSIS) is an on-board method to generate and supply nitrogen-enriched air (NEA) to the fuel tank. EGSIS combines a polymer electrolyte membrane (PEM) electrolyzer anode which dissociates water to evolve oxygen, and a PEM fuel cell cathode which reduces oxygen from atmospheric air to produce NEA at its outlet. This paper represents the first attempt to model and simulate EGSIS using a three-dimensional, steady state, isothermal model. Various EGSIS performance indicators such as current density, reactant concentration distribution, and polarization curves are studied as a function of operating conditions and design parameters. The results from the computational model are validated against our previous experimental results for various operating conditions. The simulation results reveal the effects of temperature, reactant flowrates, and material property optimization on EGSIS performance. Different operating strategies are explored with the goal of improving system performance.

Experimental Study on the Performance of an Onboard Hollow-Fiber-Membrane Air Separation Module

Onboard air separation devices, based on hollow fiber membranes, are traditionally used for the optimization of aircraft fuel tank inerting systems. In the present study, a set of tests have been designed and executed to assess the air separation performances of these systems for different air inlet temperatures (70°C∼110°C), inlet pressures (0.1∼0.4 MPa), volume flow rates of nitrogen-enriched air (NEA) (30∼120 L/min) and flight altitudes (1.5∼18 km). In particular, the temperature, pressure, volume flow rate, and oxygen concentration of air, NEA and oxygen-enriched air (OEA) have been measured. The experimental results show that the oxygen concentration of NEA, air separation coefficient, and nitrogen utilization coefficient decrease with the rising of air inlet temperature, air inlet pressure, and flight altitude. The effect of air inlet pressure on the above three parameters is significant, while the influence of air inlet temperature and flight altitude is relatively small.

Computational Model for Electrochemical Gas Separation and Inerting System

In July 1996, TWA flight 800 crashed into the Atlantic Ocean only 12 minutes after takeoff killing all 230 people on board. After a 4-year investigation into this catastrophe, the National Transportation Safety Board concluded that the accident was probably caused by the explosion of flammable fuel vapor in the Boeing 747’s center fuel tank. Following this landmark incident new regulations for aircraft fuel tank inerting were developed to prevent such explosions. Fuel tank inerting is the process of reducing the flammability of the fuel vapor by restricting the oxygen concentration in the ullage (air volume above the fuel) to a safe value – 12% for commercial aircraft and 9% for military aircraft. Generally, inerting is carried out by driving oxygen out the ullage using an inert gas like nitrogen.Existing inerting technologies include systems like liquid nitrogen, explosion suppressant foam, halon extinguishment, and on-board inert gas generation systems (OBIGGS). Compared to other techniques, OBIGGS is seen as viable option since nitrogen enriched air (NEA) can be produced during flight by supplying pressurized air into separation modules that preferentially retain nitrogen while allowing oxygen to escape. However, such systems are expensive and consume substantial amounts of energy, while also undergoing premature failure. Additionally, the NEA generation rate is fixed in such systems, whereas the actual NEA requirement depends on the aircraft’s flight stage. Thus, incumbent technologies are designed based on the highest demand making them overweight and expensive.Here, we propose a novel on-board electrochemical gas separation and inerting system (EGSIS) to overcome such problems. EGSIS is an electrically powered system that can be used to produce and supply NEA to the fuel tank. It combines a polymer electrolyte membrane (PEM) electrolyzer anode wherein water is dissociated to generate oxygen, and a PEM fuel cell cathode where oxygen from the inlet air inlet is reduced to produce humidified NEA as the output gas. After proper dehumidification, the NEA can be supplied directly to the ullage to reduce its oxygen concentration. Unlike current technologies, the NEA production rate in EGSIS can be easily varied with demand just by controlling the voltage applied to the system. Experimental investigations of EGSIS have been previously conducted by our group. This paper represents the first attempt to model and simulate EGSIS.We present a two-dimensional mathematical model of a single cell EGSIS that provides a foundation for the simulation and analysis of a full-scale EGSIS module. A single phase, two-dimensional, steady state, isothermal model is implemented in an EGSIS cell using COMSOL. Various EGSIS performance parameters such as current densities, reactant concentration distributions, and polarization curves are investigated as a function of operating voltage and temperature. The model involves the material properties of the various components including the polymer electrolyte membrane, the catalyst later and gas diffusion media; the transport of water vapor and air in the anode and cathode flow field channels, respectively; the transport of protons and water in the catalyst layer and the membrane; and the transport of electrical charge in the solid phase. The governing equations include continuity and steady-state incompressible Navier-Stokes equations. Additionally, species transport is modeled using the generalized Stefan-Maxwell equations whereas the Butler-Volmer equation is employed for charge transport. All of these coupled model equations are solved by the finite element method using the COMSOL Multi physics software package. The results from the computational model are then compared and validated with our experimental results for various operating conditions. Different operating strategies are explored with the goal of improving system performance. The simulated results reveal the influence of temperature, reaction flowrate, and optimized material properties on EGSIS performance. This model also provides a base for future research into the effect of alternate catalysts and gas diffusion media. It also serves as a foundation for the analysis of a practical EGSIS stack.

Gas\u2013liquid mass transfer characteristics of aviation fuel scrubbing in an aircraft fuel tank

Dissolved oxygen evolving from aviation fuel leads to an increase in the oxygen concentration in an inert aircraft fuel tank ullage that may increase the flammability of the tank. Aviation fuel scrubbing with nitrogen-enriched air (NEA) can largely reduce the amount of dissolved oxygen and counteract the adverse effect of oxygen evolution. The gas–liquid mass transfer characteristics of aviation fuel scrubbing are investigated using the computational fluid dynamics method, which is verified experimentally. The effects of the NEA bubble diameter, NEA superficial velocity and fuel load on oxygen transfer between NEA and aviation fuel are discussed. Findings from this work indicate that the descent rate of the average dissolved oxygen concentration, gas holdup distribution and volumetric mass transfer coefficient increase with increasing NEA superficial velocity but decrease with increasing bubble diameter and fuel load. When the bubble diameter varies from 1 to 4 mm, the maximum change of descent rate of dissolved oxygen concentration is 18.46%, the gas holdup is 8.73%, the oxygen volumetric mass transfer coefficient is 81.45%. When the NEA superficial velocities varies from 0.04 to 0.10 m/s, the maximum change of descent rate of dissolved oxygen concentration is 146.77%, the gas holdup is 77.14%, the oxygen volumetric mass transfer coefficient is 175.38%. When the fuel load varies from 35 to 80%, the maximum change of descent rate of dissolved oxygen concentration is 21.15%, the gas holdup is 49.54%, the oxygen volumetric mass transfer coefficient is 44.57%. These results provide a better understanding of the gas and liquid mass transfer characteristics of aviation fuel scrubbing in aircraft fuel tanks and can promote the optimal design of fuel scrubbing inerting systems.

Electrochemical gas separation and inerting system

Following the TWA 800 flight disaster in 1996 which was attributed to an explosion in the fuel tank, inerting of the ullage (air volume above the fuel in the tank) has gained prominence. Fuel tank inerting is the process of reducing the flammability of the ullage by supplying it with an inert gas like nitrogen. Current inerting techniques are expensive, consume large amounts of energy, and fail prematurely. Here, we propose a novel in-flight electrochemical gas separation and inerting system (EGSIS) to produce and supply nitrogen-enriched air (NEA). EGSIS combines a polymer electrolyte membrane (PEM) fuel cell cathode with a PEM electrolyzer anode to generate humidified NEA as the cathode output which can be dehumidified and supplied directly to the fuel tank. The required rate of NEA varies during a typical flight and a major advantage of EGSIS is that the rate of NEA generation can be conveniently controlled by varying the voltage applied to the system. Here, we report on the performance of a single-cell EGSIS apparatus and evaluate its suitability for aircraft fuel tank inerting.

Nitrogen enriched air for Nox reduction in Diesel engine

This paper analyzes the impact of nitrogen enriched air on emissions, in cylinder pressure, heat released during the working cycle and fuel consumption of a diesel engine. The experiment was performed on a naturally aspirated single cylinder diesel engine by increasing the nitrogen concentration supplied through a cylinder and NOx, CO, THC emissions were all measured with the help of a five gas analyzer. It was observed that enriching the inlet air with nitrogen decreases the NOx concentration considerably with a penalty on hydrocarbon emissions and thus the fuel conversion efficiency.

{MC COMMENT: PA CORRECTION}Theoretical study of ullage washing with mixed inert gas in a non-equilibrium state

The Mixed Inert Gas (MIG) produced by the novel Green OnBoard Inerting Gas Generation System (GOBIGGS) mainly consists of carbon dioxide, nitrogen and oxygen. Because of the large solubility of carbon dioxide in jet fuel compared with nitrogen, the no gas release or equilibrium model could not be employed any more. In this paper, first, a mathematical model of the ullage washing was set up to predict the variation of the oxygen concentration on ullage and in the fuel, and the gas evolution and dissolution rate were calculated by Fick’s second law. Then, an experimental apparatus was constructed to verify the accuracy of the model. Finally, the numerical comparisons of ullage washing using Nitrogen Enriched Air (NEA) and MIG are presented under various flow rates and fuel loads, and the result reveals that the variation of the oxygen concentration on ullage is nearly identical whatever the inert gas is NEA or MIG. However, the variation of the oxygen concentration in the fuel is disparate, and the oxygen concentration decreases rapidly if the inert gas is MIG, especially when the fuel load is low or the flow rate of the inert gas is high. Besides, MIG could suppress the rising trend of the oxygen concentration on ullage when the aircraft ascends if the fuel tank is fully washed into an equilibrium state on ground.

Simulation Calculation of Flow Characteristics of Air Separation System Based on Flowmaster

The air separation system is an important part of aircraft fuel inerting system, which is responsible for the important task of supplying nitrogen-enriched air to the aircraft fuel tank. The flow characteristic of air separation device is the key problem of its design. In this paper, based on one-dimensional fluid simulation software Flowmaster, we did some research on the simulation model of membrane modules, established the simulation model of air separation system, obtained the simulation results of the flow characteristics and analyzed the results in detail. The results showed that under low pressure and flow conditions, compared with the experimental values, the relative error of nitrogen-enriched air and oxygen-enriched air flow rate was about 5%.In the case of high inlet pressure and flow, the pressure loss of the junctions and the long pipeline was larger, and the inlet pressure, outlet pressure and pressure loss of the 12 membrane modules were significantly different. The research work was of reference value for the design optimization of air separation system in aircraft fuel inerting system.

Acute hemodynamic changes by breathing hypoxic and hyperoxic gas mixtures in pulmonary arterial and chronic thromboembolic pulmonary hypertension

BackgroundThere is insufficient evidence to counsel patients with pulmonary hypertension undergoing altitude or air travel. We thus aimed to study hemodynamic response of patients with pulmonary arterial or chronic thromboembolic pulmonary hypertension (PAH/CTEPH) during changes in inspiratory oxygen partial pressure. Methods and resultsConsecutive patients undergoing right heart catheterization had hemodynamic assessments whilst breathing ambient air (normoxia, FiO2 0.21, at altitude 490 m), nitrogen-enriched air (hypoxia, FiO2 0.16, simulated altitude 2600 m) and oxygen (hyperoxia, FiO2 1.0), each for 10 min. Data from patients with PAH/CTEPH with mean pulmonary artery pressure (mPAP) ≥25 mmHg, pulmonary artery wedge pressure ≤15 mmHg, were compared to data from controls, mPAP <20 mmHg.28 PAH/CTEPH-patients, 15 women, median age (quartiles) 62y (49;73), mPAP 35 mmHg (31;44), PaO2 7.1 kPa (6.8;9.3) and 16 controls, 12 women, 60y (52;69), mPAP 18 mmHg (16;18), PaO2 9.5 kPa (8.5;10.6) were included. Hypoxia reduced the PaO2 in PAH/CTEPH-patients by median of 2.3 kPa, in controls by 3.3 kPa, difference (95%CI) in change 1.0 (0.02 to 1.9), p < 0.05. Corresponding changes in pulmonary vascular resistance, mPAP and cardiac output were nonsignificant in both groups. Hyperoxia decreased mPAP in PAH/CTEPH-patients by 4 mmHg (2 to 6), in controls by 2 mmHg (0 to 3), difference in change 3 mmHg (0 to 5), p < 0.05. ConclusionsIn patients with PAH/CTEPH, very short-term exposure to moderate hypoxia similar to 2600 m altitude or during commercial air travel did not deteriorate hemodynamics. These results encourage studying the response of PAH/CTEPH during daytrips to the mountain or air travel.

Experimental comparison between aircraft fuel tank inerting processes using NEA and MIG

Fuel tank inerting technologies are able to reduce the fire risk by injection of inert gas into the ullage or fuel, the former called ullage washing and the latter fuel scrubbing. The Green On-Board Inert Gas Generation System (GOBIGGS) is a novel technology based on flameless catalytic combustion, and owning to its simple structure and high inerting efficiency, it has received a lot of attentions. The inert gas in the GOBIGGS is mainly comprised of CO2, N2, and O2 (hereinafter, Mixed Inert Gas (MIG)), while that in the On-Board Inert Gas Generation System (OBIGGS), which is one of the most widely used fuel tank inerting technologies, is Nitrogen-Enriched Air (NEA). The solubility of CO2 is nearly 20 times higher than that of N2 in jet fuels, so the inerting capability and performance are definitely disparate if the inert gas is selected as NEA or MIG. An inerting test bench was constructed to compare the inerting capabilities between NEA and MIG. Experimental results reveal that, if ullage washing is adopted, the variations of oxygen concentrations on the ullage and in the fuel are nearly identical no matter the inert gas is NEA or MIG. However, the ullage and dissolved oxygen concentrations of MIG scrubbing are always higher than those of NEA scrubbing.

Draining Water from Aircraft Fuel Using Nitrogen Enriched Air

This paper concerns a computational study of the process of removing water from an aircraft’s fuel tank by pumping nitrogen enriched air (NEA) from the bottom of the tank. This is an important procedure for the smooth, efficient, and safe operation of the aircraft’s engine. Due to the low partial pressure of water in the pumped NEA, it absorbs water from the fuel. The water-laden bubbles enter the ullage, the empty space above the fuel, and escape into the environment. The effects of the number of NEA inlets and the NEA mass flow rate on the timescale of the NEA pumping were investigated using Computational Fluid Dynamics. The results reveal that the absorption of water by the NEA bubbles is low and is not affected by the number of the inlets used. Yet, the water content in the fuel decreases fast during the procedure, which is the desired outcome. We show that this is due to the relatively dry NEA entering the ullage and displacing the moist air, thus reducing the partial pressure of water at the fuel/ullage interface. This shift from equilibrium conditions forces water to evaporate from the fuel’s entire surface. Furthermore, the amount of water migrating from the fuel directly into the ullage is significantly greater than that absorbed by the rising bubbles. In turn, the rate of decrease of the water content in the ullage is determined by the total NEA mass flow rate and this is the dominant contributor to the draining time, with the number of NEA nozzles playing a minor role. We confirmed this by pumping NEA directly into the ullage, where we observe a significant decrease of water even when the NEA is not pumped through the fuel. We also show that doubling the mass flow rate halves the draining time. When considering the capability of most modern aircraft to pump NEA through the fuel as part of their inerting system, the proposed method for removing water is particularly attractive, requiring very little (if at all) design modification.

Analytical investigation into the effects of nitrogen enriched air bubbles to improve aircraft fuel system water management

In the aircraft fuel system, water–ice contamination within fuel tanks has been one of the most serious challenges. This issue was highlighted in 2008 by an accident triggered by restricted fuel flow due to the ice formation within the system. The on-board inert gas generation system, which is already installed on some aircraft to prevent the outbreak of fire in the fuel tank, is a potentially feasible method to improve the water management. This paper focuses on the impact of bubbles from the on-board inert gas generation system system on water in the fuel tank. In order to explore the bubble effect, the relationship between orifice configuration and bubble parameter was investigated by means of mathematical models and existing experimental data. Moreover, by combining a MATLAB code and the introduced bubble model, the effect of bubble size and rising speed on the water contamination in the fuel tank was observed. For the water absorption process, a new model was introduced using a mass transfer coefficient. Finally, this article concludes that the amount of accumulated water is dependent on the bubble size and rising speed, and an optimal bubble size or speed is predictable once the coefficient has been obtained.

P209 Effect of normobaric hypoxia on pulmonary hemodynamics in patients with precapillary pulmonary hypertension

Introduction: Patients with precapillary pulmonary hypertension (PH, pulmonary arterial or chronic thromboembolic pulmonary hypertension, PAH/CTEPH) may experience disease deterioration upon exposure to a hypoxic environment during air travel or altitude sojourns due to hypoxic pulmonary vasoconstriction. We investigated the effect of breathing a hypoxic air mixture on pulmonary hemodynamics and blood gases in PH in comparison with unaffected controls. Methods: Patients scheduled for diagnostic right heart catheterization had hemodynamic assessments under ambient air (FiO2 0.21) and after 10 min of breathing nitrogen-enriched air (hypoxia FiO2 0.16). Patients were stratified according to their mean pulmonary arterial pressure (mPAP): PH (mPAP ≥25mmHg, pulmonary artery wedge pressure (PAWP) ≤15mmHg), unaffected controls (patients undergoing RHC for evaluation of dyspnea with mPAP< 20mmHg) and intermediate (mPAP 20-24mmHg). Results: 20 patients with PH (12 females, 8 PAH, 12 CTEPH; mean±SD age 63±14y), 12 controls (12 females, age 63±7y) and 7 patients from the intermediate group (3 females, age 66±12y) were included. PaO2 significantly decreased in all groups upon exposure to hypoxia (see table). However, hypoxemia was not accompanied by significant changes in mPAP or cardiac index in any group. Unexpectedly, pulmonary vascular resistance significantly increased in the control group. The test was well tolerated by all participants.TablePAH/CTEPH (n=20)Intermediate (n=7)Controls (n=12)FiO2 0.21Mean Change 95%CI with FiO2 0.16FiO2 0.21Mean Change 95%CI with FiO2 0.16FiO2 0.21Mean Change 95%CI with FiO2 0.16Heart Rate, bpm70±94 (1 to 7)*78±123 (0 to 6)68±95 (2 to 9)*mPAP, mmHg40.5±12.22.6 (-0.1 to 5.2)23.9±4.20.7 (-3.5 to 4.9)16.7±1.71.7 (-0.2 to 3.6)Cardiac index, l/min/m22.6±0.7-0.04 (-0.3 to 0.2)5.2±1.90.04 (-0.5 to 0.6)3.2±0.9-0.1 (-0.4 to 0.1)PVR index, WU6.1±3.30.7 (-0.2 to 1.7)1.3±0.40.04 (-0.5 to 0.6)1.8±0.70.6 (0.1 to 1.0)*SaO2(%)93.9±3.5-7.4 (-12.2 to -2.6)**95.7±2.8-4.4 (-10.0 to 1.1)97.3±1.5-4.9 (-7.8 to -2.0)**PaO2 (kPA)9.3±1.6-2.5 (-3.4 to -1.6)***10.4±1.7-2.7 (-5.2 to -0.3)*10.7±1.4-3.3 (-4.5 to -2.1)***PaCO2 (kPA)4.6±0.5-0.3 (-0.5 to -0.1)*4.8±1.9-0.6 (-1.4 to 0.1)4.4±1.0-0.2 (-0.7 to 0.3)Abbreviations: mPAP: mean pulmonary artery pressure; PVR: pulmonary vascular resistance; SaO2: arterial oxygen saturation; PaO2: partial pressure of oxygen; PaCO2: partial pressure of carbon dioxide. Note: Data are given as mean±SD. Within group differences *: p<0.05; **: p<0.01; ***: p<0.001. Between group differences in the changes upon exposure to hypoxia were not statistically significant. Open table in a new tab Abbreviations: mPAP: mean pulmonary artery pressure; PVR: pulmonary vascular resistance; SaO2: arterial oxygen saturation; PaO2: partial pressure of oxygen; PaCO2: partial pressure of carbon dioxide. Note: Data are given as mean±SD. Within group differences *: p<0.05; **: p<0.01; ***: p<0.001. Between group differences in the changes upon exposure to hypoxia were not statistically significant. Conclusions: Our data suggest that a short-term exposure to a moderately reduced FiO2 in patients with PAH/CTEPH associated with chronic hypoxemia in sea level conditions seems not to further exacerbate derangements in pulmonary hemodynamics. Whether the hemodynamic effects of a short hypoxic challenge are in concordance with the response to prolonged hypoxia remains to be determined.

Experimental Study of an On-board Fuel Tank Inerting System

A simulated aircraft fuel tank inerting system was established and experiments were conducted to investigate the performance of the system. The system uses hollow fiber membrane which is widely used in aircraft as the air separation device and a simplified 20% scale multi compartment fuel tank as the inerting object. Experiments were carried out to investigate the influences of different operating parameters on the inerting effectiveness of the system, including NEA (nitrogen-enriched air) flow rate, NEA oxygen concentration, NEA distribution, pressure of bleeding air and fuel load of the tank. Results showed that for the multi compartment fuel tank, concentrated flow washing inerting would cause great differences throughout the distribution of oxygen concentration in the fuel tank, and inerting dead zone would exist. The inerting effectiveness was greatly improved and the ullage oxygen concentration of the tank would reduce to 12% successfully when NEA entered three compartments evenly. The time span of a complete inerting process reduced obviously with increasing NEA flow rate and decreasing NEA concentration, but the trend became weaker gradually. However, the reduction of NEA concentration will decrease the utilization efficiency of the bleeding air. In addition, the time span can also be reduced by raising the pressure of bleeding air, which will improve the bleeding air utilization efficiency at the same time. The time span decreases linearly as the fuel load increases.

Experimental study of an aircraft fuel tank inerting system

In this work, a simulated aircraft fuel tank inerting system has been successfully established based on a model tank. Experiments were conducted to investigate the influences of different operating parameters on the inerting effectiveness of the system, including flow rate of the inert gas (nitrogen-enriched air), inert gas concentration, fuel load of the tank and different inerting approaches. The experimental results show that under the same operating conditions, the time span of a complete inerting process decreased as the flow rate of inert gas was increased; the time span using the inert gas with 5% oxygen concentration was much longer than that using pure nitrogen; when the fuel tank was inerted using the ullage washing approach, the time span increased as the fuel load was decreased; the ullage washing approach showed the best inerting performance when the time span of a complete inerting process was the evaluation criterion, but when the decrease of dissolved oxygen concentration in the fuel was also considered to characterize the inerting effectiveness, the approach of ullage washing and fuel scrubbing at the same time was the most effective.

Research on the Stratified Charge Control of the Nitrogen-Enriched Intake Air

Nitrogen-enriched intake air (NEA) can reduce the formation of NOx by inhibiting the combustion temperature in cylinder. This paper discusses the research progress on engines using NEA. The result indicates that nitrogen-enriched air can reduce engine NOx emissions remarkably. Besides, this paper analyzes the basic characteristics of the stratified charge control of the nitrogen-enriched intake air. In order to optimize the nitrogen stratification charge, a new nitrogen direct injection engine of stratified charge has been designed.

Bubbles, microparticles, and neutrophil activation: changes with exercise level and breathing gas during open-water SCUBA diving

The study goal was to evaluate responses in humans following decompression from open-water SCUBA diving with the hypothesis that exertion underwater and use of a breathing mixture containing more oxygen and less nitrogen (enriched air nitrox) would alter annexin V-positive microparticle (MP) production and size changes and neutrophil activation, as well as their relationships to intravascular bubble formation. Twenty-four divers followed a uniform dive profile to 18 m of sea water breathing air or 22.5 m breathing 32% oxygen/68% nitrogen for 47 min, either swimming with moderately heavy exertion underwater or remaining stationary at depth. Blood was obtained pre- and at 15 and 120 min postdive. Intravascular bubbles were quantified by transthoracic echocardiography postdive at 20-min intervals for 2 h. There were no significant differences in maximum bubble scores among the dives. MP number increased 2.7-fold, on average, within 15 min after each dive; only the air-exertion dive resulted in a significant further increase to 5-fold over baseline at 2 h postdive. Neutrophil activation occurred after all dives. For the enriched air nitrox stationary at depth dive, but not for other conditions, the numbers of postdive annexin V-positive particles above 1 μm in diameter were correlated with intravascular bubble scores (correlation coefficients ∼0.9, P < 0.05). We conclude that postdecompression relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation appear to exist, but more study is required to improve confidence in the associations.