A Comparison of Low-Pressure and Supercharged Operation of Polymer Electrolyte Membrane Fuel Cell Systems for Aircraft Applications

Multifunctional fuel cell systems are competitive solutions aboard future generations of civil aircraft concerning energy consumption, environmental issues, and safety reasons. The present study compares low-pressure and supercharged operation of polymer electrolyte membrane fuel cells with respect to performance and efficiency criteria. This is motivated by the challenge of pressure-dependent fuel cell operation aboard aircraft with cabin pressure varying with operating altitude. Experimental investigations of low-pressure fuel cell operation use model-based design of experiments and are complemented by numerical investigations concerning supercharged fuel cell operation. It is demonstrated that a low-pressure operation is feasible with the fuel cell device under test, but that its range of stable operation changes between both operating modes. Including an external compressor, it can be shown that the power demand for supercharging the fuel cell is about the same as the loss in power output of the fuel cell due to low-pressure operation. Furthermore, the supercharged fuel cell operation appears to be more sensitive with respect to variations in the considered independent operating parameters load requirement, cathode stoichiometric ratio, and cooling temperature. The results indicate that a pressure-dependent self-humidification control might be able to exploit the potential of low-pressure fuel cell operation for aircraft applications to the best advantage

CHARACTERISTICS OF PEMFC OPERATION IN AMBIENT AND LOW PRESSURE ENVIRONMENT CONSIDERING THE FUEL CELL HUMIDIFICATION

This paper summarizes experimental results of an air-fed polymer electrolyte membrane fuel cell system HyPM XR 12 (Hydrogenics Corp.) considering fuel cell temperature, stoichiometry, and load requirement variations at ambient and low-pressure operation. The experimental work realized at a low-pressure test facility designed and assembled by the German Aerospace Center, Institute of Engineering Thermodynamics is based on an experimental design. The experimental results confirm reduced fields of fuel cell operation as well as a decreased gross stack performance and efficiency at low operating pressures (950 mbar C p C 600 mbar) for the defined fuel cell temperature, stoichiometry, and load requirement. In addition, indexes of the operating parameters are introduced, characterizing the fuel cell operation with regard to the gross stack performance and efficiency at ambient and low-pressure levels. The discussion of the results considers analyses of fuel cell humidification

Phase II trial of weekly 24-hour infusion of gemcitabine in patients with advanced gallbladder and biliary tract carcinoma

BACKGROUND: Patients with advanced gallbladder and biliary tract carcinoma face a dismal prognosis, as no effective palliative chemotherapy exists. The antitumor effect of gemcitabine is schedule-dependent rather than dose-dependent. We evaluated the activity of a prolonged infusion of gemcitabine in advanced gallbladder and biliary tract carcinomas. METHODS: Nineteen consecutive eligible patients were enrolled. All patients were required to have histologically confirmed diagnosis and measurable disease. Gemcitabine was infused over 24 hours at a dose of 100 mg/m(2 )on days 1, 8, and 15. Treatment was repeated every 28 days until progression of disease or limiting toxicity. Tumor response was evaluated every second course by computed tomography (CT) scans. RESULTS: Eighteen patients were evaluable for response. A total of 89 cycles of therapy were administered. One partial response was observed (6%; 95% confidence interval (CI): 0–27%) and ten additional patients had stable disease for at least two months (disease control rate 61%; 95% CI: 36–83%). The therapy was well tolerated, with moderate myelosuppression as the main toxicity. The median time to tumor progression and median overall survival was 3.6 months (95% CI 2.6–4.6 months) and 7.5 months (95% CI 6.5–8.5 months), respectively. CONCLUSION: Weekly 24-hour gemcitabine at a dose of 100 mg/m(2 )is well tolerated. There was a relatively high rate of disease control for a median duration of 5.3 months (range 2.8–18.8 months). However, the objective response rate of this regimen in gallbladder and biliary tract carcinomas was limited

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children

Multifunctional fuel cell system in an aircraft environment: An investigation focusing on fuel tank inerting and water generation

Implementing a proton exchange membrane fuel cell (PEMFC) into an aircraft environment is a challenging task. In order for aircraft manufacturers and airlines to realize the ecological and economic benefits of this technology, it is necessary to make use of the multiple functions that a fuel cell system can provide. In addition to the main product of electrical energy, the fuel cell is capable of delivering further products, which are useful in an aircraft environment. The waste products – water vapor, heat and oxygen-depleted air (ODA) – at the cathode exhaust are valuable for use on board a commercial airplane. This paper describes the multifunctional approach, points out the advantages of the operation strategy as well as describes a prototype system for the multifunctional use of a PEM fuel cell on board a commercial airplane. The stable operation of the aforementioned system was successfully demonstrated in various tests. The emphasis of the work in question is on water and ODA generation/conditioning

Merkmale des PEMFC-Betriebes bei Umgebungs- und Unterdruckbedingungen

In diesem Beitrag werden die Ergebnisse experimenteller Untersuchungen zur Beschreibung eines luftatmenden PEMFC-Brennstoffzellensystems HyPM XR 12 (Hydrogenics Corp.) in Abhängigkeit der Brennstoffzellenkühltemperatur, der Stöchiometrie und der Lastanforderung bei Umgebungs- und Unterdruckbedingungen (AC-Bedingungen) vorgestellt. Die experimentellen Daten wurden an einem Unterdruckteststand am Deutschen Zentrum für Luft- und Raumfahrt, Institut für Technische Thermodynamik nach einem D-optimalen Verfahren der statistischen Versuchsplanung erhoben. Im Ergebnis der Untersuchungen bestätigt sich, dass eine Verringerung des Betriebsdruckes bis p = 600 mbar bei definierter Brennstoffzellenkühltemperatur, Stöchiometrie und Lastanforderung zur Verringerung des Betriebsfeldes bei gleichzeitiger Verringerung der Brennstoffzellenleistung und -effizienz führt

Pressure-Dependent Operation of Polymer Electrolyte Membrane Fuel Cells; Exemplified by Aircraft Applications

The pressure-dependent operation of polymer electrolyte membrane fuel cell systems is considered, following a general research methodology. Based on previous research a model refinement from a phenomenological mathematical model towards a semi-empirical mathematical model is presented. It is shown that for the fuel cell device under test and the chosen compressor a low-pressure operation in suction mode is more efficient compared to the supercharged operation. This matter of fact permits optimized operating and control strategies for (multifunctional) fuel cell systems for aircraft applications

Fuel Cell Systems for a Greener Aviation

The trend in new civil aircraft’s development is toward “more electric” aircraft and green sky. Fuel cell systems as possible part of the electrical supply in civil aircraft can allow reaching this target. Indeed fuel cell systems have high electrical efficiency, which can be used for on ground power generation and emergency power on flight, and are only producing water and oxygen depleted air as gas emissions. What it is also very innovative is that this “waste products” can be used to generate water on board and inert gas for the jet fuel tank as fire retardation and suppression measure. For several years the Institute of Technical Thermodynamics of the German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in cooperation with Airbus developed fuel cell systems which fulfil these functionalities for both aircraft ground and cruise operation. The main achievements of the last past years are the Antares-H2 development and tests as well as the successful milestones passed with the research aircraft DLR ATRA with fuel cell system test. This paper presents all the modelling and experimental activities of the DLR on fuel cell development for aircraft