Aircraft Power Research Articles

Data-driven discovery of dynamics for control

The ability to discover physical laws and governing equations from data is one of humankind’s greatest intellectual achievements. A quantitative understanding of dynamic constraints and balances in nature has facilitated rapid development of knowledge and enabled advanced technology, including aircraft, combustion engines, satellites, and electrical power. There are many more critical data-driven problems, such as understanding cognition from neural recordings, inferring patterns in climate, determining stability of financial markets, predicting and suppressing the spread of disease, and controlling turbulence for greener transportation and energy. With abundant data and elusive laws, data-driven discovery of dynamics will continue to play an increasingly important role in these efforts. This work develops a general framework to discover the governing equations underlying a dynamical system simply from data measurements, leveraging advances in sparsity-promoting techniques and machine learning. The resulting models are parsimonious, balancing model complexity with descriptive ability while avoiding overfitting. The only assumption about the structure of the model is that there are only a few important terms that govern the dynamics, so that the equations are sparse in the space of possible functions. This perspective, combining dynamical systems with machine learning and sparse sensing, is explored with the overarching goal of real-time closed-loop feedback control of complex systems.

Secondary organic aerosol (SOA) yields from NO<sub>3</sub> radical + isoprene based on nighttime aircraft power plant plume transects

Abstract. Nighttime reaction of nitrate radicals (NO3) with biogenic volatile organic compounds (BVOC) has been proposed as a potentially important but also highly uncertain source of secondary organic aerosol (SOA). The southeastern United States has both high BVOC and nitrogen oxide (NOx) emissions, resulting in a large model-predicted NO3-BVOC source of SOA. Coal-fired power plants in this region constitute substantial NOx emissions point sources into a nighttime atmosphere characterized by high regionally widespread concentrations of isoprene. In this paper, we exploit nighttime aircraft observations of these power plant plumes, in which NO3 radicals rapidly remove isoprene, to obtain field-based estimates of the secondary organic aerosol yield from NO3 + isoprene. Observed in-plume increases in nitrate aerosol are consistent with organic nitrate aerosol production from NO3 + isoprene, and these are used to determine molar SOA yields, for which the average over nine plumes is 9 % (±5 %). Corresponding mass yields depend on the assumed molecular formula for isoprene-NO3-SOA, but the average over nine plumes is 27 % (±14 %), on average larger than those previously measured in chamber studies (12 %–14 % mass yield as ΔOA ∕ ΔVOC after oxidation of both double bonds). Yields are larger for longer plume ages. This suggests that ambient aging processes lead more effectively to condensable material than typical chamber conditions allow. We discuss potential mechanistic explanations for this difference, including longer ambient peroxy radical lifetimes and heterogeneous reactions of NO3-isoprene gas phase products. More in-depth studies are needed to better understand the aerosol yield and oxidation mechanism of NO3 radical + isoprene, a coupled anthropogenic–biogenic source of SOA that may be regionally significant.

Dripping Behavior of Wire Fire under Varying Pressure and Electric Current

Dripping of polymer insulations is a different type of hazardous behaviors in wire fire, which has a potential risk of igniting adjacent combustible material and causing the dramatic growth and spread of fire in buildings, aircraft, spacecraft and nuclear power plant. To improve the fire-safety strategy, bench scale tests are conducted to study the dripping phenomenon using thin wire sample under various atmosphere pressure and electric current. The results show that the variation of flame front has a slight fluctuation during molten dripping, while the flame size (especially flame height) changes significantly. Moreover, dripping frequency (f) decreases with pressure (Ρ) due to a sufficient burning effect, but it increases with electric current (Ι) because of a stronger accumulating effect.

A balancing act for electric aircraft power systems

A balancing act for electric aircraft power systems

Revisiting the Birth of 7YSZ Thermal Barrier Coatings: Stephan Stecura †

Thermal barrier coatings are widely used in all turbine engines, typically using a 7 wt.% Y2O3–ZrO2 formulation. Extensive research and development over many decades have refined the processing and structure of these coatings for increased durability and reliability. New compositions demonstrate some unique advantages and are gaining in application. However, the “7YSZ” (7 wt.% yttria stabilized zirconia) formulation predominates and is still in widespread use. This special composition has been universally found to produce nanoscale precipitates of metastable t’ tetragonal phase, giving rise to a unique toughening mechanism via ferro-elastic switching under stress. This note recalls the original study that identified superior properties of 6–8 wt.% yttria stabilized zirconia (YSZ) plasma sprayed thermal barrier coatings, published in 1978. The impact of this discovery, arguably, continues in some form to this day. At one point, 7YSZ thermal barrier coatings were used in every new aircraft and ground power turbine engine produced worldwide. 7YSZ is a tribute to its inventor, Dr. Stephan Stecura, NASA retiree.

Improvement of friction units of power plants by aplying ceramic composite spray coatings

Modifying the working surface of a product by applying protective and functional coatings makes possible considerable changes in the mechanical, optical, electrical, magnetic, thermal and chemical properties of the original structural material, its real surface, producing articles with protective, for example, anti-corrosion, wear-resistant and other properties. We investigated the possibility of improving the friction units of aircraft power plants by applying nanostructured ceramic composite spray coatings. A heavily loaded bearing forming a part of the gearbox of a turbojet engine is used as a prototype of the friction unit. The advantages and drawbacks of improved friction units as compared to production models and their prototypes made according to an improved technology are assessed. The results obtained during the experimental work are presented. A positive conclusion is made about the use of nanostructured composite materials in the development of friction units; the most favorable method of coating is determined.

Emissions from auxiliary power units and ground power units during intraday aircraft turnarounds at European airports

It is widely known that emissions from aircraft engines, Auxiliary Power Units (APU) and ground handling equipment contribute to air pollution at airports. During the aircraft turnaround process, the main source of emissions is the APU. The use of the APU can be significantly reduced if the aircraft stand is equipped to supply external electrical power and pre-conditioned air to the cabin. This paper analyses the actual duration of APU and external power usage during intraday aircraft turnarounds at 125 airports during June 2015. The data is derived from flight data recording units of more than 200 short-haul, narrow-body jet aircraft, conducting some 25,195 aircraft turnarounds and thus provides the most detailed assessment of aircraft power usage available. A common practice is for the APU to be running for a short period on arrival at the stand (arrival-cycle) and then again for a short period prior to departure (departure-cycle). It is identified in this study that departure-cycle emissions are three times greater than arrival-cycle emissions. These emissions could be reduced if more accurate forecasts of departure times are available to flight crew. The provision of external ground power is found to reduce emissions by up to 47.6%. However, the study also highlights that when the source of external power is a diesel-fuelled mobile Ground Power Unit (GPU), there is a net doubling in emissions of hydrocarbons. APU usage is also observed to vary with outside air temperature (OAT) leading to possible increases in emissions of up to 6%.

On conventional versus direct ageing of Alloy 718

Alloy 718 is a Ni-based superalloy commonly used for parts of aircraft engines and power plants where very high demands on high-temperature yield strength, creep and corrosion resistance must be met. Polycrystalline parts such as turbine discs are industrially manufactured via hot-forging followed by solution annealing and dual ageing to form nanoscale γ′ and γ" precipitates. However, through the alternative process of ‘direct ageing’, increased yield strength contributions of ∼10% can be achieved while maintaining sufficient creep resistance. In addition to this so-called ‘direct ageing effect’, the omission of solution annealing between forging and ageing is economically attractive. Therefore, to date, direct ageing is widely implemented in the production of forged aerospace parts. However, the detailed mechanisms behind the direct ageing effect yet remain unclear. We present a correlative microscopy approach to identify the detailed microstructural evolution during conventional versus direct ageing. Our results confirm higher dislocation densities, lower δ-phase volume fractions and the absence of selected γ-matrix grain growth, as suggested in previous research. However, a key finding reported here via the use of atom probe microscopy is a remarkable structuring within and between the nanoscale γ′ and γ" precipitation. Not only do we find an increase in both the volume fraction and size of the γ" precipitates after direct ageing, we report a prevalence of stacked co-precipitation in various sequences depending on the nucleation condition. The findings are summarized in a microstructural model for conventional and direct ageing.

AIRCRAFT POWER SUPPLY SYSTEM DESIGN PROCESS AS AN AUTOMATION OBJECT

The process of designing aviation electrical power systems (EPS) is related to the need to fulfill a number of requirements of normative and technical documents and to conduct a large number of calculations. Experience has shown that it is not possible to obtain reliable initial data on the nature and magnitude of electricity consumption by electricity receivers (end users) at the early stages of design. The composition of the electric power receivers and the power consumption of electricity during the design process are repeatedly changed. This leads to the need to repeatedly perform tasks related to the synthesis of primary and secondary systems of generation and calculation. The desire to improve the efficiency of EPS led to the emergence of new standardized types of electrical energy - 270 V DC and 380 V three-phase AC of stable and unstable frequency. It follows that it is possible to implement a rather large number of options for EPS structures, and there may be several secondary EPS or, in general, EPS of a third or higher level. The lack of ready-made aviation energy converters implies the impossibility of using ready-made components, and the development of specific devices should be coordinated with the development of EPS. In this case, one of the results of EPS design will be a set of requirements for the devices and units of the EPS projected. In any case, the design process for EPS aircraft requires a lot of iterations that take into account the change in both the raw data and the constraints on the EPS elements and the design process itself. The traditional approach to the design of EPS aircraft, assuming the knowledge of the designer of dozens of GOSTs (State All-Union standards) and OSTs (All-Union standarts) regulating the design stages of EPS, as well as the existence of standard EPS structures, from which a specific choice is made, is practically impossible at present. The only way to consciously approach the problem of designing EPS aircraft and take into account all the requirements of the customer and the regulatory and technical documentation is its automation. Automation of the design of EPS aircraft as an optimization task involves the formalization of the object of optimization, as well as the choice of the criterion of efficiency and control actions. Under the object of optimization in this case we mean the design process of the EPS, the formalization of which includes formalization and the design object – the aircraft power supply system.

Intracerebrovascular enzyme replacement therapy for CLN2 disease: A collaborative, multi-disciplinary approach

This chapter briefly reviews the different applications of natural circulation systems (NCSs) in various industries. Closed-loop NCSs are extensively used in solar water heaters, geothermal, fossil-fueled, and nuclear power plants. In addition, these systems are used in component-cooling applications such as transformers, electronic devices such as computer chips, and gas turbines. Although NCSs are mainly employed as heat transport devices, they can be engineered for noncooling applications such as passive controls, liquid fins, and study of low-velocity corrosion and deterministic chaos. Examples of open-loop natural circulation applications include solar chimneys, buoyancy pumps, air lift pumps, and building ventilation. The largest applications of NCSs are possibly in the chemical process industries. However, the highest power operating NCSs can be found in fossil-fueled power plants. The ESBWR (Economic Simplified Boiling Water Reactor) is the highest power (4500 MW) NCS designed so far. Mini loops with heat transport capability of the order of a few tens of Watts also can be found in the electronics industry.Some of the emerging applications of NCSs are in passive cooling of aircraft, vehicles, building ventilation, and solar thermal power plants. Due to the energy-saving potential of natural circulation, its application is increasing in various industry sectors. Natural circulation applications in electronics device cooling, solar thermal power plants, and residential buildings are expected to increase in the near future. In addition, its passive functioning without operator action or signal is important for enhanced safety and reliability of nuclear reactors, increasing their applications in the nuclear field.

Digital Generator Control Unit Design for a Variable Frequency Synchronous Generator in MEA

Variable frequency power generation systems have been adopted for modern aircraft power systems, thus, a new generator control unit (GCU) must be designed to regulate the output voltage and obtain high quality power supply under a wide frequency range from 360 Hz to 800 Hz. In this paper, a dual digital signal processor (DSP) structure-based GCU was proposed. Multi-loop control structure was adopted with the controller parameters varying adaptively at different working conditions to obtain better performance. Different root-mean-square (RMS) calculation algorithms have been compared and the final RMS calculation scheme was determined to realize the trade-off between accuracy and computing efficiency. Experimental results show considerable performance improvements of the generator output voltage under various operating conditions with the proposed GCU.

Exploiting the synergy between aircraft architecture and electric power system in unmanned aerial vehicle through many-objective optimisation

This study addresses the preliminary design of a fixed-wing, tailsitter electric unmanned aerial vehicle (with vertical take-off and landing capability) by optimising the size of the powertrain components together with the main aircraft design specification. To this scope, different optimisation problems are considered, with two, three and four objective functions, respectively. The results of the optimisation are used not only to compare the performance of different optimisation algorithms when increasing the number of goals, but also to discuss the synergy between architecture and power systems optimisation.

Improving the Efficiency of Gas Turbines During Off-Design Operation by Adjusting the Turbine and Compressor Blade Stagger Angles

Gas turbines in general and aircraft engines in particular undergo frequently dynamic operations. These operations include the routine start-up, load change and shut downs to cover their operation envelope. The frequency of the dynamic operation depends on the size of the engines and the field of application. Engines for commuter aircrafts and particularly helicopter engines operate more often in an off-design mode compared to large commercial aircraft engines and power generation gas turbines. During these routine operations, the compressor mass flow, the pressure ratio, the combustion chamber fuel and air mass flow as well as turbine mass flow change. These changes affect the engine aerodynamic performance and its efficiency. To avoid the inception of rotating stall and surge, high performance gas turbines are equipped with mechanisms that adjust the stator stagger angles thus aligning the stator exit flow angle to the rotor inlet angle, which reduces an excessive incidence. The reduction of incidence angle not only preserves the stable operation of the compressor, but it also prevents the compressor efficiency from deterioration. The existence of an inherent positive pressure gradient may cause the boundary layer separation on compressor blades leading to the rotating stall and surge. Such condition, however, does not exist in a turbine, and therefore, there has been no compelling reason to apply the blade adjusting method to the turbine component. For the first time, the impact of turbine blade stagger angle adjustment on the gas turbine efficiency during the operation is shown in this paper. Given a statistically distributed load condition, the extensive dynamic simulation reported in this paper shows how the efficiency can be positively affected through proper blade adjustment. For the time dependent operation, the code GETRAN developed by the author was enhanced to include the turbine blade adjustment as a function of time. To conduct the dynamic simulation with turbine stator stagger angle adjustment during a dynamic operation, the full geometry of the Brown Boveri GT-9 gas turbine was utilized. Starting from the reference stagger angle, it is varied within an incidence range of ± 3 degree. Detailed simulation results show the substantial efficiency improvement through stator stagger blade adjustment.

Exploiting the synergy between aircraft architecture and electric power system in unmanned aerial vehicle through many-objective optimisation

This study addresses the preliminary design of a fixed-wing, tailsitter electric unmanned aerial vehicle (with vertical take-off and landing capability) by optimising the size of the powertrain components together with the main aircraft design specification. To this scope, different optimisation problems are considered, with two, three and four objective functions, respectively. The results of the optimisation are used not only to compare the performance of different optimisation algorithms when increasing the number of goals, but also to discuss the synergy between architecture and power systems optimisation.

An Improved PWM Strategy for Z-Source Inverter With Maximum Boost Capability and Minimum Switching Frequency

Z-source inverter provides a competitive single-stage dc–ac power conversion with the capability of both buck and boost voltage regulation. In order to maximize voltage gain and to increase efficiency, this paper proposes an improved pulse-width modulation (PWM) strategy. By adjusting the shoot-through duty ratio of one-phase leg, it regulates the average value of intermediate dc-link voltage, which is the same as the instantaneous maximum of three-phase line voltage in one switching time period $(T_{s})$ . And the other two-phase legs maintain the fixed switching states. Thus, the equivalent switching frequency of power devices in the inverter bridge is reduced to $1/ 3f_{s}$ ( $f_{s}$ is the frequency corresponding to $T_{s}$ ). The operating principles and closed-loop controller design are analyzed and verified by simulation and experiments. Compared with the existing PWM strategies, the improved PWM (IPWM) strategy demonstrates higher efficiency under full operation range of low voltage gain (1.27-2) application. However, with the IPWM strategy, the inductor current and capacitor voltage contain six-time-line-frequency ripples, which consequently require large size of the passive components when the output frequency is very low. Thus, it is also suitable for 400–800-Hz medium frequency aircraft and vessel power supply system due to a relatively high output line frequency. Furthermore, the idea of IPWM strategy can be extended to other kinds of three-phase impedance network-based inverters.

Reignition After Interruption of Intermediate-Frequency Vacuum Arc in Aircraft Power System

Intermediate frequency (IF) electric power supply system has been widely applied in airplanes. Reignition after interruption of 360-850 Hz vacuum arc in axial magnetic field (AMF) is studied in this paper. According to the experimental results, the current interruption ability decreases from 22.4 kA at 360 Hz to 14.0 kA at 850 Hz. With the increase of frequency, the rate of change of current, di/dt, at current zero (CZ) reaches the breaking threshold at a smaller current value. Based on the least squares solution of the Mayr model, the time of decay of arc energy is prolonged when interruption fails, which is disadvantageous to the breaking process. On the other hand, the eddy effect is enhanced by higher frequency, which increases the residual magnetic induction intensity and the hysteresis phase of AMF after CZ. As a result, the diffusion of plasma is blocked. In the experiments, we find that the position of arc reignition always appears at the margin of contacts. It is shown by calculation that the electric field at the marginal area is twice as strong as that inside the contact. The current density is high, where the electric field is strong, leading to the higher probability of field emission. Arc images are analyzed by frame differential method. The sputtering velocity of macroscopic particles is estimated to be 10-20 m/s. The dissipation time of the macroscopic particles is longer than the arc time of IF vacuum arc, and the presence of macroscopic particles leads to the arc reignition. The findings of this paper would be beneficial to the parameter design of IF vacuum circuit breakers, such as the magnetic flux density of AMF, the chamfering of contact margin, and contact materials.

Synchronous Online Diagnosis of Multiple Cable Intermittent Faults Based on Chaotic Spread Spectrum Sequence

This paper proposes a method based on chaotic spread spectrum sequence for synchronous online diagnosis of intermittent faults for complex and cable. networks, such as the aircraft power system. The novelties of the proposed method include: 1) since chaotic spread spectrum signals are sensitive to initial values, the number of chaotic sequences are not limited and the proposed method is not limited by the number of cables under monitoring; 2) with the self-correlation characteristic and cross-correlation characteristic of chaotic sequence, the proposed method can be extended to online diagnosis of multiple cable intermittent faults; and 3) the signal source impedance amplification method is proposed for intermittent arc faults of multiple cables, which improves the reflection coefficient and increases the accuracy of online detection and location of intermittent arc faults. A series of simulations and experiments on multiple cables with different intermittent fault modes are conducted to verify the effectiveness of the proposed approaches.

Minimal Cut Sets-Based Reliability Evaluation of the More Electric Aircraft Power System

The More Electric Aircraft (MEA) stands for the direction of aviation development in the new era, and the reliability of power systems on the MEA has attracted widespread attention. Based on the characteristics of MEA power systems, an equivalent method of electrical topology structure is presented in this article, and evaluation method is proposed which shows the reliability of the overall system with the reliability of specific nodes. Firstly, electrical topology structure of a MEA power system is converted into a network node diagram according to the proposed equivalent method. Then, the minimal path sets of specific nodes are obtained by the adjacent matrix algorithm, and the low-order minimal cut sets of disjointed are obtained. After that, the actual failure rate of components is converted to node failure rate, and the reliability of the overall system is evaluated by operational reliability indexes of specific nodes. Finally, taking the MEA A380 as an example, this paper compares and analyzes the reliability of AC loads, DC loads, and key loads to verify the validity and feasibility of the proposed evaluation method. This evaluation system can predict the weak points existing in the MEA power system, as well as providing theoretical support for maintenance schedule.

230 VAC/28 VDC high‐power density power supply for more electric aircraft applications

The most important characteristics of aircraft power system are power density, reliability, availability and power quality. The traditional more electric aircraft (MEA) 28 VDC network is used to power the core electronic system. However, the 28 VDC network in modern MEAs such as B787 or A380 is a centralised power network obtained by transformer rectifier unit (TRU), battery charge and rectifier unit (BCRU) or two-stage power conversion (AC/DC + DC/DC) from 230 VAC, 400–800 Hz variable frequency input. The traditional centralised architecture is of low-power density and low fault tolerance. Furthermore, compared to distributed power network, the centralised architecture is of less availability inherently, therefore a single-stage, isolated, low-power and high-power density power supply is required to achieve the distributed 28 VDC network. In this study, a three-phase single-switch discontinuous mode AC–DC flyback converter is proposed. The converter directly rectifies a three-phase, 400–800 Hz, 230 VAC network into a 28 VDC network. The operation modes of the converter are analysed. A prototype is carefully designed and implemented using high-frequency planner transformer and SiC MOSFET techniques, aiming at higher performance. Experimental results demonstrate the practicability and high performance of the proposed power supply system.

Study on high speed traction drive CVT for aircraft power generation (Analysis of ratio-changing response)

Study on high speed traction drive CVT for aircraft power generation (Analysis of ratio-changing response)