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In order to reduce the late maintenance cost of CRH2 EMU, avoid risks in foreign procurement, and improve the overall performance of auxiliary power unit (APU), this paper presents a high-performance APU control unit with independent intellectual property rights, in order to achieve seamless replacement with the original control unit. By improving the hardware circuit of the control unit and adding Ethernet circuit, the computing power and output precision, load jump/switch response speed, communication rate and real-time fault diagnosis capability of the control unit are greatly improved. Based on that, by introducing high precision harmonic compensation control technology, the harmonic suppression ability of the converter under nonlinear load and the output voltage quality of the APU are improved. Type test, combination test and reliability test of the designed APU are carried out, and the comparison test between the APUs with the designed control unit and the original one is also completed. The results show that the performance of the designed APU is better than that of the deployed one. The harmonic content of output voltage of the APU decreases from 3.9% to 1.6% under the nonlinear full load condition, which achieving the requiremant of seamless replacement with the original one.

This study aims to investigate the environmental and economic impacts of implementing fuel cell and battery-based hybrid configurations. Phosphoric acid and molten carbonate fuel cell systems in the place of diesel generators of a large tanker to supply the vessel's total electricity demand. Environmental and economic analyses of the utilization of the specified fuel cell systems with LiNiCoALO 2 and LiNiMnCoO 2 chemical types of battery cells on a large marine vessel are provided in this paper. In addition, the assessment of the most suitable battery cell and charge-discharge hours for fuel cell systems is carried out with a grid-search algorithm. Six different fuel cell and battery configurations are investigated to obtain the optimum system layout. The results show that the CO 2 emissions could be reduced by up to 49.75% and the lowest electricity production cost is found as 0.181 $/kWh for the current fuel prices with the utilization of molten carbonate fuel cells and LiNiMnCoO 2 battery cells. • Performance comparison between PAFC and MCFC was performed. • Lowest electricity production cost was obtained 0.181 $/kWh. • CO 2 emission of the marine vessel decreased by 49.75%. • MCFC and LiNiMnCoO 2 battery were best option among other cases studied. • Fuel cell-battery hybrid system could reduce fuel consumption by 25.6%. [ABSTRACT FROM AUTHOR]

In this paper, the development and implementation of a novel approach for fault detection of an aircraft auxiliary power unit (APU) has been demonstrated. The developed approach aims to target the proactive identification of faults, in order to streamline the required maintenance and maximize the aircraft's operational availability. The existing techniques rely heavily on the installation of multiple types of intrusive sensors throughout the APU and therefore present a limited potential for deployment on an actual aircraft due to space constraints, accessibility issues as well as associated development and certification requirements. To overcome these challenges, an innovative approach based on non-intrusive sensors i.e., microphones in conjunction with appropriate feature extraction, classification, and regression techniques, has been successfully demonstrated for online fault detection of an APU. The overall approach has been implemented and validated based on the experimental test data acquired from Cranfield University's Boeing 737-400 aircraft, including the quantification of sensor location sensitivities on the efficacy of the acquired models. The findings of the overall analysis suggest that the acoustic-based models can accurately enable near real-time detection of faulty conditions i.e., Inlet Guide Vane malfunction, reduced mass flows through the Load Compressor and Bleed Valve malfunction, using only two microphones installed in the periphery of the APU. This study constitutes an enabling technology for robust, cost-effective, and efficient in-situ monitoring of an aircraft APU and potentially other associated thermal systems i.e., environmental control system, fuel system, and engines. • Novel online monitoring system for aircraft auxiliary power unit. • Acoustic-to-thermodynamic parameter estimation model proposed for fault diagnostics. • Acoustic feature extraction and regression techniques evaluated on near-field data. • Multiple faults can be detected using the proposed scheme with high accuracy. • The proposed system can estimate the parameters in real time using two microphones. [ABSTRACT FROM AUTHOR]

Auxiliary Power Unit (APU) is an indispensable component utilized in modern aircraft, which provides electrical and pneumatic power to the aircraft independently. What's more, APU can help the main engines restart in case of main engine failure during flight. Thus there exists the need of APU monitoring. However, APU has not received sufficient attention in maintenance due to its relatively low cost and safety requirements compared to main engines. Line maintenance shows that APU is likely to fail in the start stage. Based on the Quick Access Recorder data supported by the airline, a fault detection method for APU is proposed in this paper. In order to improve the accuracy of fault detection, feature selection is carried out firstly to determine the optimal subset of monitoring parameters by Recursive Feature Elimination. Then fault detection is carried out by Support Vector Machine. Results show that Exhaust Gas Temperature is the most effective index among all monitoring parameters, and feature selection has a significant improvement on the accuracy of fault detection, which means higher accuracy with less monitoring cost. The method proposed in this paper also disposes that some monitoring parameters should be paid more attention in terms of the condition monitoring of APU. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change contributes to increased frequency and intensity of droughts, wildfires, storms, coastal sea level rise, and population displacements, in addition to causing lung and cardiovascular diseases from the emission of Criteria Air Pollutants (CAPs). The aviation sector is estimated to contribute 2%–3% of global anthropogenic Greenhouse Gas (GHG) emissions. This excludes GHG emissions from airport operation and maintenance activities due to limited research in the area. This systematic literature review examined the Life Cycle Assessment (LCA) carried out by previous studies on the environmental impacts of airport operation and maintenance activities. This allows to assess existing literature on the impacts of these activities; identify knowledge gaps in LCA based on the findings of the review; and propose areas for further research and improvement in mitigating the environmental impacts of airport operation and maintenance activities. A total of 11 papers were selected for thematic analysis and narrative synthesis following a systematic review process based on the research question which yielded a total of 263 peer‐reviewed research articles and dissertations on the topic. The findings of the review showed that knowledge gaps exist in the LCA of environmental impacts of Auxiliary Power Units (APU) and Ground Support Equipment (GSE) operations in the airport during aircraft turnaround time. Further research is suggested in the use of feasible and affordable alternative energy sources (electricity, compressed natural gas, liquefied petroleum gas, and hydrogen) at airports to reduce the environmental impacts associated with petrol‐ and diesel‐powered GSE and gate operations at airports. [ABSTRACT FROM AUTHOR]

In this paper, environmental impact analysis is applied to the various auxiliary power units (APUs) used for commercial aircraft in air transportation sector. The exhaust emissions of different auxiliary power units used in commercial aircraft are investigated. The emission index (EI), global warming potential (GWP) rate, global warming potential index (GWPI), environmental impact (EnI) rate, environmental impact index (EnII), environmental damage cost (EDC) rate, and environmental damage cost index (EDCI) of the exhaust emissions of APUs are computed. The GTCP36-300 model APU has the lowest total emission rate (TER) with 1.333 kg/h, the GTC85-129 model APU has the maximum total environmental index (TEI) by 24.719 g/kg-fuel, the GTCP36-300 model APU has the best total global warming potential value with 2709.176 kg/h CO2_eqv, the TSCP700 model APU has the worst global warming potential index rate as 52.481 kg/kWh CO2_eqv, the best total environmental damage cost rate is calculated to be 3.717 €/h for GTC85-72 model APU, the TSCP700 model APU has the highest environmental damage cost index with 0.130 €/kWh, the maximum total environmental impact is computed to be 5656.378 mPts/h for GTCP660 model APU, and the best total environmental impact index is determined for the GTC85-72 model APU. [ABSTRACT FROM AUTHOR]

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In the power control process of the range extender, both the engine and the generator are at risk of reaching the torque output limit. The limitation not only comes from the restriction of their own torque output capacity, but also comes from the additional constraints that are established to avoid power reverse undershoot. In order to improve the system performance under time-varying torque constraints, a real-time model predictive controller (MPC) that manipulates the torque commands of the engine and the generator to track the reference power is designed. Different from the traditional penalty function method, the quadratic function is taken as the penalty function in this paper, which greatly improves the efficiency of solving the optimal solution. Meanwhile, the steady-state torque command in the feasible region is taken as the extreme point of the quadratic penalty function, which avoids the penalty coefficient tending to infinity. By adjusting the penalty coefficients of different constraints, the overall optimal solution approaches the boundary of the active inequality constraints. And according to the Karush-Kuhn-Tucker (KKT) condition, it is proved that the optimal solution of the original problem can be obtained through iteration. The effectiveness and practicability of the proposed strategy are evaluated through numerical simulations on Simulink and experiments on a range extender. [ABSTRACT FROM AUTHOR]

A helicopter auxiliary power unit (APU) is initially equipped with a hydro-mechanical control system (HMC). Because HMC's complex structure is difficult to be modified to realize sophisticated control algorithms and the APU is faced with the need for performance improvement, it is urgently necessary to carry out digital control modification of HMC. Based on the analysis of control laws of the original HMC and differences between HMC and digital control system, key techniques involved in the digital control system are studied, such as overall structure, control laws and fuel system based on electric fuel pump, and finally a full authority digital electronic control system (FADEC) is developed for APU. Functions, performances and key techniques of the FADEC system are evaluated on test rig, and the test results show functions of original control system are enhanced and performances of APU are improved more effectively under the control of the designed FADEC compared with the original HMC.

Auxiliary power unit is one of the indispensable systems for civil aviation aircraft but the traditional planned maintenance cannot meet the actual needs of airlines. In this work, the key performance parameters of the auxiliary power unit are selected by using recursive feature elimination method. With the selected parameters, the remaining useful flight cycle of the auxiliary power unit is predicted by applying particle filter techniques. Some improved algorithms such as Gaussian particle filter and auxiliary particle filter are also compared. The experimental results demonstrate that the particle filter-based method has high prediction accuracy and engineering application value. [ABSTRACT FROM AUTHOR]

Modern commercial aircraft are usually configured with aircraft condition monitoring system to collect the operating data of subsystems and components, which can be used for airborne system health monitoring and predictive maintenance. This paper presents a baseline model based aircraft auxiliary power unit performance assessment and remaining useful life prediction method using aircraft condition monitoring system reports data, which can facilitate a cost-effective management of auxiliary power units of aircraft fleet. Firstly, the performance baseline model for auxiliary power unit is established using random forest method. Then a health index characterizing the performance degradation of in-service auxiliary power units is obtained based on the performance baseline model. Finally, the performance degradation trend is predicted using Bayesian dynamic linear model. To improve the prediction accuracy, four performance baseline models are established from the data of auxiliary power units under different operating conditions, among which an optimal model is determined. This data-driven baseline model can be used to quantify the performance degradation of auxiliary power units in service, and can be further used to evaluate the remaining useful life of auxiliary power unit using a Bayesian dynamic model. The developed approach is applied on a real data set from 22 auxiliary power units of a commercial aircraft fleet. The results show that the computed health index can effectively characterize the auxiliary power units performance degradation and the remaining useful life relative prediction errors are less than 4% when auxiliary power unit enters the rapid degradation stage. This would allow operators to accurately assess the performance degradation for the auxiliary power units and further proactively plan future maintenance events based on remaining useful life prediction. [ABSTRACT FROM AUTHOR]

Current commercial and heavy-duty powertrains are geared towards emissions reduction. Energy recovery from exhaust gases has great potential, considering the mechanical work to be transferred back to the engine. For this purpose, an additional turbine can be implemented behind a turbocharger; this solution is called turbocompounding (TC). This paper considers the adaptation of turbine wheels and gearboxes of small turboshaft and turbojet engines into a two-stage TC system for a six-cylinder opposed-piston engine that is currently under development. The initial conditions are presented in the first section, while a comparison between small turboshaft and turbojet engines and their components for TC is presented in the second section. Based on the comparative study, a total number of 7 turbojet and 8 turboshaft engines were considered for the TC unit. [ABSTRACT FROM AUTHOR]

The article presents a starter-generator system for an auxiliary power unit of an aircraft. A feature of the presented system is the use of a synchronous generator with excitation from permanent magnets and a semiconductor converter. The main problem of the system is the generation of electric energy of an aircraft on the basis of a synchronous generator with excitation from permanent magnets is the absence of the possibility of regulating the voltage and frequency of electrical energy, in this connection, a semiconductor converter that ensures the conversion of generated electric energy with significant mass-dimensions characteristics.The article proposes an approach to designing a starter-generator system with a parallel connection of a synchronous generator with excitation from permanent magnets and a semiconductor converter. This approach makes it possible to significantly reduce the part of the electrical energy that needs to be converted, as a consequence, the semiconductor converter has significantly smaller mass-and-batch characteristics.In the article the modes of generation of electric energy and the starter mode of operation of the starter-generator system are considered in detail, the circuit realization of the semiconductor converter is shown. A scheme for replacing one phase of the system for generating electric energy and calculating electric parameters is presented.The possibility of creating a highly efficient starter-generator system based on a synchronous generator with excitation from permanent magnets and a semiconductor converter for an auxiliary power plant of aircrafts is shown. Structural and basic schemes for constructing a system for generating electrical energy are proposed. The approach to the choice of rational circuit solutions is substantiated, basic estimates of the electrical parameters of the system are obtained. The possibility of achieving a specific mass of a semiconductor converter for synchronous generators of 0.21÷0.33 kg/kW is shown.

A complete fuel cell-based auxiliary power unit in the 7.5 kWe power class utilizing diesel fuel was developed in accordance with the power density and start-up targets defined by the U.S. Department of Energy. The system includes a highly-integrated fuel processor with multifunctional reactors to facilitate autothermal reforming, the water-gas shift reaction, and catalytic combustion. It was designed with the help of process analyses, on the basis of which two commercial, high-temperature PEFC stacks and balance of plant components were selected. The complete system was packaged, which resulted in a volume of 187.5 l. After achieving a stable and reproducible stack performance based on a modified break-in procedure, a maximum power of 3.3 kWe was demonstrated in a single stack. Despite the strong deviation from design points resulting from a malfunctioning stack, all system functions could be validated. By scaling-up the performance of the functioning stack to the level of two stacks, a power density of 35 We l−1 could be estimated, which is close to the 40 We l−1 target. Furthermore, the start-up time could be reduced to less than 22 min, which exceeds the 30 min target. These results may bring diesel-based fuel cell auxiliary power units a step closer to use in real applications, which is supported by the demonstrated indicators.

A quick, low energy consuming and reliable start-up is essential for fuel cell systems utilizing diesel and jet fuel. A compact fuel processor for coupling with a high-temperature polymer electrolyte fuel cell is developed with electrically-heated reactors in the 28 kW th power class. Based on this set-up, start-up strategies are developed and validated. With the basic strategy, 14 min are required in the best case to commence reforming and achieve self-sustaining operation with desired CO concentration at full load using NExBTL diesel and, respectively, 16 min using Jet A-1. However, using premium diesel, the basic strategy leads to a strong increase in the concentrations of ethane and benzene. An advanced strategy enables 16 min start time with premium diesel suppressing these undesired side products. This result is within the 30 min start-up time target for auxiliary power units for 2020 and offers a reliable option for real world applications. • 28 kW th fuel processor for diesel and jet fuel designed, built and tested. • Full electric start using integrated heating wires in reformer and shift reactor. • Start of autothermal reforming in 8.5 min. • Self-sustaining operation with desired reformate quality at full power in 14 min. • Advanced start strategy to suppress a strong formation of undesired side products. [ABSTRACT FROM AUTHOR]

Abstract The autothermal reforming of middle distillates is a favored reforming technique for fuel cell-based auxiliary power units (APUs) in the transport sector. The efforts made in recent years to produce a high quality reformate have been reflected in a variety of improvements to the reactors and mode of operation of the fuel processing systems. By these means, the concentrations of contaminants, especially traces of hydrocarbons in the gas phase, frequently drops below the previous detection limit. In this paper, a new GC/MS method is developed to reduce the detection limit of the analytics into the sub-ppm range. This work is intended to serve as a valuable step to showing which traces of hydrocarbons can still be qualitatively and quantitatively expected in a high quality reformate. This contribution may help determine the multitude of hydrocarbonous substances that can have a detrimental long-term effect on catalysts and adsorbents in a fuel cell-based APU system operated with middle distillates. Highlights • GC/MS method was optimized to find hydrocarbon trace in sub-ppm range. • Multitude of contaminants in a high quality diesel reformate where identified. • 12 Representative contaminants up to C 7 were quantitatively determined. [ABSTRACT FROM AUTHOR]

Using a gas turbine energy unit as an example, the article discusses possible ways for forcing the short-term gas turbine engines (GTE). The introduction explains the need for forcing the air transport and marine GTE in specific driving conditions and offers the main methods. Then it analyzes the three main short-term forcing methods according to GTE power, namely: precompressor water injection, a short-term rise in temperature after the combustion chamber, and feeding an additional compressed air into combustion chamber from the reserve cylinders.The analysis of the water injection method to force a GTE presents the main provisions and calculation results of the cycle, as a function of engine power on the amount of water injected into compressor inlet. It is shown that with water injection into compressor inlet in an amount of 1% of the total airflow there is a 17% power increase in the compressor. It also lists the main implementation problems of this method and makes a comparison with the results of other studies on the water injection into compressor.Next, the article concerns the GTE short-term forcing method through the pre-turbine short-term increase in the gas temperature. The article presents the calculation results of the cycle as a function of the power and the fuel-flow rate on the gas temperature at the turbine inlet. It is shown that with increasing temperature by 80 degrees the engine power increases by 11.2% and requires 11% more fuel. In the analysis of this method arises an issue of thermal barrier coating on the blade surface. The article discusses the most common types of coatings and their main shortcomings. It lists the main challenges and some ways of their solving when using this method to implement the short-term forcing.The last method under consideration is GTE short-term forcing by feeding the compressed air into the combustion chamber from the additional reserve cylinders. It should be noted that this method is applied only to small-sized and auxiliary gas turbines, operating as part of gas turbine power plants in vehicles, which comprise additional compressed air cylinders. Here are calculation results as a function of the engine power and forcing time on the amount of additional compressed air fed into the combustion chamber. The article shows that in feeding the additional compressed air in the amount of 15% of the airflow the engine power in the compressor is increased by 27%. It also describes the main implementation difficulties of this method.In conclusion, the article presents data on the considered methods for short-term forcing the GTE and shows the main difficulties in their implementation. It also comes to conclusion that the electro-generator design strength and characteristics restrict the limits of these short-term forcing methods.

Current commercial and heavy-duty powertrains are geared towards emissions reduction. Energy recovery from exhaust gases has great potential, considering the mechanical work to be transferred back to the engine. For this purpose, an additional turbine can be implemented behind a turbocharger; this solution is called turbocompounding (TC). This paper considers the adaptation of turbine wheels and gearboxes of small turboshaft and turbojet engines into a two-stage TC system for a six-cylinder opposed-piston engine that is currently under development. The initial conditions are presented in the first section, while a comparison between small turboshaft and turbojet engines and their components for TC is presented in the second section. Based on the comparative study, a total number of 7 turbojet and 8 turboshaft engines were considered for the TC unit.

The brief presents some principles of the ON/OFF operational strategy applied to energy management of a hybrid internal combustion engine (ICE) based auxiliary power unit (APU). It is shown that significant reduction of fuel consumption (78% for the example system presented) and maintenance expenses (80% operation time decrease was attained by the system) may be achieved by such a strategy, shifting the system operation point towards corresponding optimal region. The side effect of aggravated amount of starting events is cured by employing an actively balanced supercapacitor (SC)-based emergency starter (SCS). The SCS operates as short-time energy storage device, charging from the battery at a low rate and then providing a current burst required for proper internal combustion engine starting. Current sensorless method of automatic connection (based on bus voltage sensing) and disconnection (based on sensing the voltage across bidirectional MOSFET-based switch) of the SCS is also proposed. The proposed circuitry, successfully validated by experiments, may be arbitrarily scaled up or down according to application rating.

A diesel fuel processor for high temperature polymer electrolyte fuel cells in the 5 kW e power class was developed and tested. Emphasis was placed on a quick and sustainable start-up. Furthermore, operational conditions were identified that would achieve the desired reformate quality for the fuel cell anode. A thermal start-up strategy using a commercial diesel burner was developed and further optimized, resulting in a hybrid strategy with the help of a glow plug. With this strategy, self-sustaining operation of the fuel processor at full load was achieved in 27 min and the resulting reformate was of sufficient quality to operate the fuel cell in 31 min. The experimental plan includes operation periods of between 4 and 24 h with start/stop/regeneration cycles representing the daily operation of an auxiliary power unit at maximum load. With all fuels used, the target carbon monoxide concentration of 1% at the anode inlet (wet reformate) was achieved. Significant deviations from the design parameters were necessary to demonstrate a stable system performance with desulfurized Jet A-1 and to achieve the target carbon monoxide concentration with premium diesel. These results bring diesel fuel processing for auxiliary power units closer to real application, offering experimentally-validated solutions for start-up and stable operation under realistic conditions with different fuels on a systems level. [ABSTRACT FROM AUTHOR]

Recently, metal-based solid oxide fuel cells (SOFCs) receive much attention for potential application in auxiliary power units (APUs). In this study, a sinter-joining method with a silver bonding layer is proposed. This method enables the fabrication of metal-based SOFCs by joining metal plates and conventional ceramic cells using a silver bonding layer. This sinter-joining method has the advantage of full-sintering of the cathode at 1100 °C, which facilitates a lower area specific resistance (ASR) of the cathode. Furthermore, the entire manufacturing process is conducted under air atmosphere. A 5 × 5 cm 2 metal-based cell is successfully fabricated by the sinter-joining method, and a maximum power density of 433 mW cm −2 and a low polarization resistance of 0.12 Ω cm 2 is obtained. Using the metal-based cells, a prototype 3-cell SOFC stack is developed considering mechanical robustness and diesel reformate fuel supply for future APU system applications. The stack exhibits a maximum power density of 100 mW cm −2 and is tested for 120 h. After the test, a post-mortem analysis is conducted, and the causes of the low electrochemical performance and degradation issue are investigated. In the conclusion, the sinter-joining method is considered as one of the methods for metal-based SOFCs. [ABSTRACT FROM AUTHOR]

This review brings together publications in the form of articles, reports, theses and patents related to the use of solid oxide fuel cells in aircraft with a focus on replacing the current auxiliary units with a hybrid system. The potential advantages and main challenges of the new technology are reported, indicating some possible trends in this technology. However, even after many studies, some initial challenges remain. For example, the hybrid system did not achieve the necessary weight-efficiency-ratio, and there seems to be no consensus on the choice of the best fuel. We conclude that the most viable short-term applications appear to be unmanned units, particularly because of security issues and low technology maturity. Smaller power applications, in which the new system is responsible for peripheral services such as a power supply for air conditioning, toilets, and heating up food, are candidates to enter the market in the short or medium term. In the long term, applications for fully electric aircraft and clean fuels will certainly be the focus of larger aircraft manufacturers. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes operation and optimization of an onboard reforming system for an auxiliary power unit solid oxide fuel cell (SOFC APU) system for trucks that use liquid natural gas as fuel. The reformer system is based on partial oxidation and produces a reformate gas flow sufficient for a 100 W fuel cell. The ALMUS AG concept and configuration of the SOFC APU unit is described. The paper presents analyses of the efficiency of the partial oxidation reformer. The selected catalyst AB10 is analyzed under various reaction temperatures and molar ratios of CH4:air. Two reforming reactor configurations are tested; both with 5 g of the catalyst. The optimal operating conditions for the reactor are proposed. The reformer is currently operated in an electric furnace that simulates the actual system and condition in a combustion chamber. The main focus is to obtain stable operation with high hydrogen yield and low coke deposition. The paper presents analyses of a 1,000 h partial oxidation stability test. The demonstration of the performance of the CPOX reformer confirms the system applicability. The observed slow catalyst deactivation is attributed to the detected coke deposition. The change to the structure of deposited coke along the reactor is explained. [ABSTRACT FROM AUTHOR]