Air Path Research Articles

Phase-Sensitive Open-Path Dual-Comb Spectroscopy with Free-Running Combs

Open-path dual-comb spectroscopy has emerged as a promising technique for regional multigas monitoring with its conspicuous advantages of broadband spectral coverage, high spectral resolution, and rapid update rate. However, it is challenging to realize its full potential due to the undesirable mutual coherence of the dual-comb source and turbulence in the air path, which hinder it from field-deployed open-path applications. Here, phase-sensitive open-path dual-comb spectroscopy based on free-running combs is reported, in which dual-purpose compensation is proposed to provide immunity against both the time jitter of comb sources and turbulent noise. Broadband and high-fidelity atmospheric amplitude and phase spectra containing gas absorption and dispersion information over a 900-m turbulent air path are acquired. For the rovibrational resonances of ${\mathrm{CO}}_{2}$ and ${\mathrm{H}}_{2}\mathrm{O}$ in 6250--6660 ${\mathrm{cm}}^{\ensuremath{-}1}$, the achieved residual of the amplitude spectrum is no more than 0.01, and the average residual of the phase spectrum is 0.2 mrad, corresponding to about 0.2 as of relative timing noise or a refraction-index change of about 6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}$ over the target path. The precision of concentration retrieval is about 3 ppm for ${\mathrm{CO}}_{2}$ in 30 s. A simulated gas-leakage measurement validates the dynamic monitoring capability of this system. This highly effective noise-compensation method provides the possibility of deploying the portable configuration and holds the potential to propel environmental protection and atmospheric science.

Study on the Path and Thermal Characteristics of the Spark Discharge Between Ice and Electrode Gap

The corona-to-spark transition is a fundamental discharge process between the ice and electrode gap, the first step of a partial arc formation on the ice-covered insulators. This article set up a calibrated Schlieren system synchronized with electrical signals to study the primary process and characteristics of the corona-to-spark transition between ice and electrode gap. The Schlieren system is calibrated by a Plano lens and verified with a thermocouple; a series of experiments are set up to obtain the discharge process’s voltage, current, and temperature in the time domain. A vibration–translational model is proposed to quantitatively explain the influence of discharge path on the thermal–electrical characteristics. It is found that the brush discharge appears only in the air, which promotes the temperature rise during the corona-to-spark transition and makes the discharge’s air path have the highest temperature. The findings in this article will provide a basic understanding of the corona-to-spark transition characteristics between the electrode and ice gap.

Optimization of the air loop system in a hydrogen fuel cell for vehicle application

Hydrogen fuel cells are a potential route to decarbonize the automotive sector due to the zero CO2 tailpipe emissions, faster re-fuelling, and higher energy density than their direct competitor, the battery-electric powertrain. One of the key challenges is to find the best air path configuration to achieve high efficiency in a system level. This work aims to optimize, setup, and demonstrate a highly efficient Proton Exchange Membrane fuel cell system (PEMFC). This powerplant is hydrogen fuelled and scalable to achieve the required power output for different vehicles. This work evaluates a PEMFC by a 1D-numerical approach. The fuel cell is modelled, validated, and later studied under different air inlet conditions. The main goal is the evaluation of different air path layouts to achieve the highest system efficiency. Numerical simulations of electric compressor and coupled and de-coupled electrically assisted turbocharging are performed with different component sizes and cathode pressures. Therefore, this work provides an overview of our initial findings that will outline the key modelling challenges for fuel cell systems and then present a comparison of different air-path architectures. The coupled electrically assisted turbocharger is determined to be the best layout with an improvement of 10% of the delivered power at a high current load. The e-turbocharging optimized by the proposed methodology allows reduction of the peak electric machine electric power by 60%.

Smoke dispersion test and emergency control plan of fire in mine roadway during downward ventilation

To explore the wind flow turbulence and smoke flow diffusion law during the mine downward ventilation fire, two similar experimental platforms of a inclined single pipe test device and a loop system multiple pipe test device were built. The change data of the air flow in the pipeline during the fire period under different air volumes were measured. The evolution process of downward ventilation fire in the whole roadway network domain in Dayan Mine was simulated, and the emergency plan was put forward. The results show that in the experiment, the combustion intensity of the fire source is positively correlated with the ventilation power, and the fire wind pressure increases with the increase of the inclination angle of the pipeline. The throttling effect of the fire area and the combustion of the fire source together make the air volume in the pipeline change rapidly. The critical wind speed that makes the downward ventilation flow fire wind pressure equal to the fan power is 1.8 m s−1. The stronger the fan capacity, the stronger the ability of the main air path to overcome the resistance of the fire zone and maintain the original state. In the simulation, the most dangerous place when the downward ventilation fire smoke is reversed is the area (weak flow area) in the mine tunnel network where the ventilation power is weaker than the fire wind power. This study can provide a theoretical basis for the formulation of emergency plans for mine fire accidents.

Global domain fluid-thermal coupling modeling method and characteristics analysis for large capacity motor

—The global domain fluid-thermal characteristics study is challenging to perform due to the complicated ventilation arrangement and enormous volume for the large capacity electric machine. This paper uses the world's largest capacity non-superconducting low-speed induction motor, 6.5 MW, as the research object and proposes a global domain fluid-thermal characteristics calculation method. Firstly, the global domain fluid field model of the inner air path is established and solved. Then, the motor is divided into five subdomains according to the ventilation structure. The flow and pressure obtained from fluid field solutions are used as coupling parameters to couple each subdomain model, and an iterative solution is carried out based on the boundary condition continuity of the adjacent subdomains. The temperature distribution of each subdomain is obtained when the temperature difference is less than 0.1%. Finally, an experimental platform is built to verify the results. The maximum relative error between calculated and measured values is 1.67% for temperature and 4.92% for fluid velocity, which verifies the developed model's rationality and the proposed method's validity.

Development of a Model-Based Coordinated Air-Fuel Controller for a 3.0 dm3 Diesel Engine and Its Assessment through Model-in-the-Loop

The tightening of diesel pollutant emission regulations has made Internal Combustion Engine (ICE) management through steady-state maps obsolete. To overcome the map’s scarce performance and efficiently manage the engine, control systems must cope with ICE transient operations, the coupling between its subsystem dynamics, and the tradeoff between different requirements. The work demonstrates the effectiveness of a reference generator that coordinates the air path and combustion control systems of a turbocharged heavy-duty diesel engine. The control system coordinator is based on neural networks and allows for following different engine-out Nitrogen Oxide (NOx) targets while satisfying the load request. The air path control system provides the global conditions for the correct functioning of the engine, targeting O2 concentration and pressure in the intake manifold. Through cooperation, the combustion control targets Brake Mean Effective Pressure (BMEP) and NOx to react to rapid changes in the engine operating state and compensates for the remaining deviations with respect to load and NOx targets. The reference generator and the two controller algorithms are suitable for real-time implementation on rapid-prototyping hardware. The performance overall was good, allowing the engine to follow different NOx targets with 150 ppm of deviation and to achieve an average BMEP error of 0.3 bar.

Experimental investigation of combustion characteristics analysis and optimization during the turbocharging mode switching process of diesel engine with advanced turbocharging system

Multi-turbocharger system is one of the major enablers of modern diesel engine performance. To meet the boosting requirements under different operating conditions is the difficulty. The two-stage sequential turbocharging (TSST) system creates the flexibility to select the turbocharging mode so that the engine benefits from efficiency and power density. However, the critical issue at hand is the unstable running, or even worse, misfire, of the engine caused by the abrupt air path shifts during the turbocharging mode switching process. Therefore, the control of the switching process is an indispensable procedure to apply the TSST system. The previous studies mainly focused on turbocharging system parameters. The combustion characteristics during switching process have been underestimated. The combustion process is influenced by the fuel and charging variations during the transient process, and it is unique compared with the steady state. In this paper, the experiments of TSST system switching process were carried out to investigate the transient combustion characteristics, formation mechanism of its fluctuation, and optimal control. The experimental results indicate that the combustion present fluctuation during the direct switching process. The main features are the generation and extinction of premixed combustion, combining the degradation and recovery of mixing-controlled combustion. The cycle history of heat-release center (CA50) presents a 3-phase fluctuation of moving backward from 9.7°CA to11.2°CA, then forward to 6.2°CA, and finally backward to 10.7°CA. The boost pressure trough is the primary factor contributing to incomplete combustion. The lowest gross indicated efficiency of 33.9 % happened at the lowest air-fuel ratio cycle. Based on the corresponding results, the substantial improvement in combustion can be ensured by regulating the switch valves in air path. When the intake switch valve opens 0.9 s later than the exhaust switch valve, the system exhibits minimal parameter fluctuations and the quickest recovery capacity. The coefficients of variation for IMEPg and CA50 are 2.7 % and 4.6 %, respectively, guaranteeing at least 39.7 % fuel conversion efficiency and only 17 cycles to reach the steady state.

Flat tube heat exchangers: Experimental analysis of frosting and water retention

In air source heat pumps, frost may form on the surface of the evaporator at low ambient air temperatures. If significant amounts of frost accumulate, the heat pump efficiency decreases so the heat exchanger needs to be defrosted. The aim of this work is an experimental analysis of different flat tube heat exchanger designs for use as direct evaporators in heat pumps. The analysis will quantify heat pump efficiency potentials in the context of cyclic frosting and defrosting conditions. For the purpose of direct evaporators in heat-release controlled heat pumps, the heat exchanger designs are studied in a heat carrier circuit under constant air heat absorption control during the frosting processes. Previous published investigations assume a constant inlet temperature, whereby the heat absorption degrades as frosting occurs. The effect of heat exchanger design on water retention from defrosting and the impact this has on the length of the refrosting phase, is analyzed experimentally. The evaluation criteria for a heat exchanger are the rate of obstruction of the air path due to frost formation and the retention of as small a mass of melt water as possible after defrosting. The heat exchanger properties fin pitch, fin overlap, and heat exchanger depth, as well as the omission of louvers and different surface coatings, are analyzed experimentally using the evaluation criteria. It is found that heat exchangers with louvered fins and an uncoated surface are advantageous for an efficient cyclic frosting and defrosting process. In the excecuted experiments a larger fin pitch of 1.4 mm can extend the frosting process up to 36% compared to a fin pitch of 1.15 mm. An increase in heat exchanger depth from 28 mm to 34 mm lenghens the frosting process by 26%. • Experimental analysis of flat tube heat exchangers under frosting conditions with constant heat absorption. • Experimental analysis of melt water drainage behaviour in vertical flat tube heat exchangers. • Investigations of heat exchanger properties fin pitch, fin overlap, depth, coatings, and omission of louvers .

Control for SI Engine Air Path System by Feedback Error Learning

Control for SI Engine Air Path System by Feedback Error Learning

Investigation of Thermopressor with Incomplete Evaporation for Gas Turbine Intercooling Systems

One of the promising ways to increase fuel and modern gas turbine energy efficiency is using cyclic air intercooling between the stages of high- and low-pressure compressors. For intercooling, it is possible to use cooling in the surface heat exchanger and the contact method when water is injected into the compressor air path. In the presented research on the cooling contact method, it is proposed to use a thermopressor that implements the thermo-gas-dynamic compression process, i.e., increasing the airflow pressure by evaporation of the injected liquid in the flow, which moves at near-sonic speed. The thermopressor is a multifunctional contact heat exchanger when using this air-cooling method. This provides efficient high-dispersion liquid spraying after isotherming in the high-pressure compressor, increasing the pressure and decreasing the air temperature in front of the high-pressure compressor, reducing the work on compression. Drops of water injected into the air stream in the thermopressor can significantly affect its characteristics. An increase in the amount of water increases the aerodynamic resistance of the droplets in the stream. Hence, the pressure in the flow parts of the thermopressor can significantly decrease. Therefore, the study aims to experimentally determine the optimal amount of water for water injection in the thermopressor while ensuring a positive increase in the total pressure in the thermopressor under conditions of incomplete evaporation. The experimental results of the low-consumption thermopressor (air consumption up to 0.52 kg/s) characteristics with incomplete liquid evaporation in the flowing part are presented. The research found that the relative water amount to ensure incomplete evaporation in the thermopressor flow part is from 4 to 10% (0.0175–0.0487 kg/s), without significant pressure loss due to the resistance of the dispersed flow. The relative increase in airflow pressure is from 1.01 to 1.03 (5–10 kPa). Based on experimental data, empirical equations were obtained for calculating the relative pressure increase in the thermopressor with evaporation chamber diameters of up to 50 mm (relative flow path length is from 3 to 10 and Mach number is from 0.3 to 0.8).

A Hybrid Degradation Evaluation Model for Aero-Engines

The non-convergence and low efficiency of the thermodynamic model make them difficult to be used in the aero-engines degradation evaluation, while the negligence of the thermodynamics process of data-driven degradation evaluation methods makes them inaccurate and hard to analyze the actual degradation of air path components. So, we propose a thermodynamic-based and data-driven hybrid model for aero-engine degradation evaluation. Different from thermodynamic-based methods, the iteration calculation is converted to the forward flow in the proposed neural network, thus improving convergence. Moreover, a multi-objective loss function considering the components co-operation process and fusion training process fully taking advantage of simulation and degradation trajectory datasets are proposed to improve the degradation evaluation accuracy. The test case is carried out on NASA’s benchmark for aero-engine degradation evaluation. The result shows that the proposed method can improve the accuracy significantly, which suggests its effectiveness.

Study of the Technologies for Freeze Protection of Cooling Towers in the Solar System

A cooling tower is an important guarantee for the proper operation of a solar system. To ensure proper operation of the system and to maintain high-efficiency points, the cooling tower must operate year-round. However, freezing is a common problem that degrades the performance of cooling towers in winter. For example, the air inlet forms hanging ice, which clogs the air path, and the coil in closed cooling towers freezes and cracks, leading to water leakage in the internal circulation. This has become an intractable problem that affects the safety and performance of cooling systems in winter. To address this problem, three methods of freeze protection for cooling towers are studied: (a) the dry and wet mixing operation method—the method of selecting heat exchangers under dry operation at different environments and inlet water temperatures is presented. The numerical experiment shows that the dry and wet mixing operation method can effectively avoid ice hanging on the air inlet. (b) The engineering plastic capillary mats method—its freeze protection characteristics, thermal performance, and economics are studied, and the experiment result is that polyethylene (PE) can meet the demands of freeze protection. (c) The antifreeze fluid method—the cooling capacity of the closed cooling towers with different concentrations of glycol antifreeze fluid is numerically studied by analyzing the heat transfer coefficient ratio, the air volume ratio, the heat dissipation ratio, and the flow rate ratio. The addition of glycol will reduce the cooling capacity of the closed cooling tower.

Bioinspired 3D-Printed Snakeskins Enable Effective Serpentine Locomotion of a Soft Robotic Snake.

We present a multi-material three-dimensional-printed snakeskin with orthotropic friction anisotropy, which permits undulatory slithering of a soft snake robot on rough surfaces. Such a snakeskin is composed of a soft skin base and embedded rigid scales attached to the robot's ventral surface. The bioinspired designs of scale shapes and arrangements lead effectively to various types of anisotropic friction, and provide means of switching robot's locomotion direction to be either the same as or opposite to the propagation direction of the traveling-wave undulation. Furthermore, steering of locomotion can be achieved by applying additional pressure bias in one air path to break symmetry of body deformation. We also successfully demonstrate the snake robot's mobility on various outdoor rough substrates, including concrete surfaces and a grass lawn, as well as pipes of different dimensions and materials, for potential field applications.

Statistical parameters of femtosecond laser pulse post-filament propagation on a 65 m air path with localized optical turbulence

High-power femtosecond laser radiation propagates nonlinearly in air, exhibiting pulse self-focusing and strong multiphoton medium ionization, which leads to the spatial fragmentation of laser pulses into highly localized light channels commonly called filaments. Filaments are characterized by high optical intensity and reduced (even zero) angular spreading and can contain laser plasma or be plasmaless (postfilaments). The presence of optical turbulence on the propagation path dramatically changes pulse filamentation dynamics and in some cases causes pulse fragmentation enhancement and collapse arrest. For the first time, to the best of our knowledge, we experimentally and theoretically investigate the transverse profile of Ti:sapphire femtosecond laser radiation nonlinearly propagating a 65 m air path to the region of postfilament evolution after passing through an artificial localized air turbulence. We show that when a turbulence layer is placed before the filamentation region, the average number of high-intensity local fluence maxima (“hot points”) in the beam profile and their sizes grow as the turbulence strength increases, and then saturates at some levels. On the contrary, the deposition of a turbulence screen within the filamentation region has almost no effect on either the number or the average diameter of postfilaments.

Research on nonlinear model predictive control of regulated two-stage turbocharging system of diesel engine at high altitudes

ABSTRACT Increasingly complex air path concepts are investigated to achieve improving the power while reducing fuel consumption of diesel engines at high altitudes. One promising technology is the Twin-VGT (variable geometry turbocharger) for diesel engines. A control concept has to be developed to exploit boost potential by coordinated management of the two turbocharger stages at different altitudes. In this paper, a nonlinear model prediction control (NMPC) algorithm based on back propagation neural network (BPNN) was proposed to purpose multi-parameter control of turbocharging system at high altitudes. Optimal control sequences of NMPC were solved by improved particle swarm optimization (PSO), and boost pressure and intake flow achieved good dynamic tracking performance by collaborative control high-pressure VGT (HVGT) and low-pressure VGT (LVGT) under whole operative conditions at high altitudes. NMPC achieved better step response performance compared with PID controller at different altitudes. NMPC control error of intake flow and boost pressure are within 0.26% under steady and transient conditions, exhibiting higher control accuracy and responsiveness even under transient operating conditions at high altitudes.

Remotely piloted aircraft system flight-plan processing from a risk-based methodology

The integration of Remotely Piloted Aircraft System (RPAS) in non-segregated airspace is one of the most demanding challenges that the aviation community must face in the years ahead. This article develops the flight-plan processing from a risk-based methodology. The risk-based methodology is underpinned by an in-depth safety analysis throughout the three temporary horizons of the Air Traffic Flow and Capacity Management system: strategical, pre-tactical and tactical. The flight-plan processing demands different measures depending on the temporary horizon. The measures mean geographical restrictions (airways or air corridors segregated for RPAS) and temporary restrictions (periods in which RPAS cannot operate). Both restrictions ensure that RPAS operation is safe and do not generate interactions with conventional aircraft. The last goal of this approach is to provide the required information to the RPAS operator based on the information available from the Network Manager (NM). The communication and information flow between the RPAS operator and the NM are detailed to validate flight-plan processing. If the initial flight plan is not affordable, the NM provides modifications during the flight-plan re-processing. The methodology is applied in the Spanish upper airspace. The results confirmed the validity and leeway of the flight-plan processing, although its implementation demands further improvements based on air traffic flow and path uncertainty.

Microwaves propagation through a small fire curtain at 3.55 GHz and 6.26 GHz and the impact on vital signs detection by using a four-element patch antenna array

The impact of the presence of a fire curtain not wider than 7 cm on an air path 150 cm long of two continuous waves at frequencies of 3.55 GHz and 6.26 GHz was quantified. Two identical patch array antennas with four linear elements were used at emission and reception and they were designed and characterized specifically for this purpose. The magnitude and phase of the transmission coefficient were measured by a vector network analyzer in all the experimental sessions. Comparing the air path and the air-plus-fire path of the waves, it resulted that fire induced shifts in magnitude and phase that depended on frequency and on the experimental setup. The heating of the antenna could have contributed to the overall observed effects. The detection of the human heartbeat by Doppler radar technique was not much influenced by the presence of fire, but the amplitude of the detected beats was increased. The array antennas produced noisy signals for the vital sign detection and the origin of this behaviour was hypothesized.

Nonlinear Propagation and Filamentation on 100 Meter Air Path of Femtosecond Beam Partitioned by Wire Mesh.

High-intensity (∼1 TW/cm and higher) region formed in the propagation of ∼60 GW, 90 fs Ti:Sapphire laser pulse on a ∼100 m path in air spans for several tens of meters and includes a plasma filament and a postfilament light channel. The intensity in this extended region is high enough to generate an infrared supercontinuum wing and to initiate laser-induced discharge in the gap between the electrodes. In the experiment and simulations, we delay the high-intensity region along the propagation direction by inserting metal-wire meshes with square cells at the laser system output. We identify the presence of a high-intensity region from the clean-spatial-mode distributions, appearance of the infrared supercontinuum wing, and occurrence of the laser-induced discharge. In the case of free propagation (without any meshes), the onset of the high-intensity zone is at 40–52 m from the laser system output with ∼30 m extension. Insertion of the mesh with 3 mm cells delays the beginning of the high-intensity region to 49–68 m with the same ∼30 m extension. A decrease in the cell size to 1 mm leads to both delay and shrinking of the high-intensity zone to 71–73 m and 6 m, respectively. Three-dimensional simulations in space confirm the mesh-induced delay of the high-intensity zone as the cell size decreases.

Application of new technologies in production of pellets at pelletizing factory at Lebedinsky GOK

Sustainable development of modern industries is ensured by continuous progression. Successful manufacture of high margin products allows Lebedinsky GOK to keep the leadership in the global metallurgy. One of such products is fluxed (high-calcium) pellets. At the same time, until recently, equipment of the pelletizing factory made such production impossible. Iron production inevitably involves dusting and toxic emission. Accordingly, one of the key trends in performance of Lebedinsky GOK is persistent reduction in the environmental impact. Aimed to cut-down dust emission, gas-cleaning units of calcination machine 4 were replaced by electric filters. The atmospheric emission of dust was largely decreased as a result. An associate beneficial effect was the lowered dynamic resistance in air and gas path, which enabled reduction in power consumption by smoke exhausters and in dustiness at working places. Fluxed (high-calcium) pelletizing needs huge amount of fluxing agents. To this effect, the second building was constructed for intake and milling of fluxing additives. After the new additive intake and milling building construction, the output of milled agents increased by 45 %. Toward maximized productivity of the hot briquetted iron plant, a package of measures was developed for increasing the content of –16+11.2 mm size in pellets. One of such measures was introduction of ROSNAMIS blades for maintaining stable slag lining in bowl pelletizers. The implemented technologies provided the high margin production output at the reduced impact exerted by the industrial activities on the environment.

Analysis and validation of the engine breather system in critical condition (in terms of maximum power)

One of the factors affecting the engine efficiency and effectiveness is the breather way of the car. Normally, the breather way for a heavy vehicle with a diesel engine is constructed according to the layout and pre-construction restrictions. The present study focuses on the designed way performance for the critical environmental conditions. This study was divided into three sections to better understand the breather way and simplify the model. Then, each section was separately examined and analyzed. The key parameters in this research are the inlet air path to the turbocharger and the outlet path of the smoke mixture from the engine to the environment. After the technical analysis, the proper operation of the breather way at the working and critical points of the engine was ensured.