Under the sponsorship of TARDEC, UTRC is developing 5–10 kW Solid Oxide Fuel Cell (SOFC) Auxiliary Power Units (APU) that will be capable of operating on JP-8 with a sulfur concentration of up to the specification’s upper limit of 3000 ppmw. These APUs will be sized to fit within the relatively tight space available on U.S. Army vehicles such as the Abrams, Bradley and Stryker. The objective of the base development program that commenced in August 2010 is a 1000 hour TRL-5 demonstration of an APU in an Abrams configuration by mid-2013. This SOFC system is expected to provide power to the 28 VDC vehicle bus at a net efficiency ≥35%. In addition, the noise level is anticipated to be far below that generated by combustion engine-based APU concepts. UTRC has completed the Preliminary Design of the system and has finalized the overall system configuration and the requirements for each of the components. During the Preliminary Design phase, evaluations of the performance of sub-scale prototypes of the desulfurizer, auto-thermal reformer, and stack were completed. In the ongoing Detailed Design phase of the program, which runs through January 2012, each of the full-scale major components will be fabricated and tested. INTRODUCTION A United Technologies Research Center (UTRC) led team is developing JP-8 fueled Solid Oxide Fuel Cell (SOFC) based vehicle Auxiliary Power Units (APUs). These systems are being designed to provide 28 VDC power efficiently (>35%) and quietly to vehicle electric loads when the main engine is off. The value proposition offered by the SOFC-APUs for the vehicle applications are twofold: 1) a decreased fuel burn relative to the provision of this power by the operation of the main engine in an inefficient near idle condition, and 2) the Proceedings of the 2011 Development of a 5 – 10 kW JP-8 Fueled Solid Oxide Fuel Cell Auxiliary Power Unit for Army Vehicle enablement of Silent Watch missions whose durations are limited only by the vehicle fuel supply. The high valuations placed upon fuel efficiency and silence for the envisioned vehicle application coupled with the requirement to provide the desired power fro a sulfur level as high as 3000 ppmw in a compact space represents an ideal scenario for the application of power dense mobile Solid Oxide Fuel Cell technology. Relative to the heat engine systems considered for the same applications, SOFCs offer large (>10%) advantages, and they are anticipated to offer appreciable acoustic benefits as well. On the other hand, relative to other fuel cell based technology, due to their high (~800°C) operating temperature, SOFC stacks can effectively on H2 and CO rich reformate streams and are more tolerant of reformate “impurities” (e.g. S) in sharp contrast to lower operating temperature stack technologies. A consequence of this increased tolerance, SOFC feature significantly more compact liquid hydrocarbon fuel processors than other technology options. However, while the high temperature operation of SOFCs is beneficial from a fuel processing standpoint, it presents an operational challenge in that the system must be b to this operating temperature before power generation commences. At present, this heat-up process is take approximately 30 minutes, and the UTRC working toward this target. SYSTEM CONCEPT UTRC has been working since 2006 under Research Lab (AFRL), TARDEC, and Defence Science and Technology Agency (DSTA) of Singapore sponsorship on the development of compact and lightweight SOFC systems Figure 1, for both Unmanned Aerial Vehicle (UAV) propulsion and vehicle auxiliary power applications that operate on low sulfur liquid hydrocarbon fuels S-8, Ultra-Low Sulfur Diesel (ULSD), and desulfurized JP 8. The major focus of the development effort has been to drive mass and volume from the SOFC systems while maintaining their efficiency advantage relative to the internal combustion engine competition for the applications. In the interest of minimizing system weight and volume at the cost of a reduced efficiency, these 1–2 kW scale systems have featured Catalytic Partial Oxidation (CPOX) fuel reformers. Under the sponsorship of the Office of the Secretary of Defense (OSD) Energy Security Task Force and with program management provided by the Office of Naval Research (ONR), UTRC migrated its lightweight SOFC system technology to 12 kW Marine Ground Generator applications, where operation on low-sulfur (< 400 ppm JP-8 and JP-5 is required, and the reduced importance of system weight in such ground applications enable incorporation of additional efficiency enhancing features Ground Vehicle Systems Engineering and Technology Symposium Page 2 of 3 m JP-8 with

ABSTRACT Intergranular glass phases can have a significant influence on the fracture resistance (R-curve behavior) of silicon nitride ceramics and appears to be related to the debonding of the β-Si 3 N 4 /oxynitride-glass interfaces. Applying the results from β-Si 3 N 4 -whisker/oxynitride-glass model systems, self-reinforced silicon nitrides with different sintering additive ratios were investigated. Silicon nitrides sintered with a lower Al 2 O 3 :Y 2 O 3 additive ratio exhibited higher steady-state fracture toughness together with a steeply-rising R -curve. Analytical electron microscopy studies suggested that the different fracture behavior is related to the Al content in the SiAlON growth band on the elongated grains, which could result in differences in interfacial bonding structures between the grains and the intergranular glass.

The effect of reactively sintered Mn1.5Co1.5O4 (MCO) coatings on the development of surface microstructure for Haynes 230 (H230) oxidized in air at 800°C has been studied using a combination of thermo-gravimetric analysis and electron microscopy techniques. The bare alloy exhibits a parabolic rate constant of 8.8×10−9mg2cm−4s−1, and forms a two-layer oxide scale with a continuous chromia layer and a thinner discontinuous MnCr2O4 overlayer. For the MCO-coated H230, the reduction step of the reactive sintering process converts the MCO coating to a mixture of Co and MnO with a thin Cr-rich oxide layer at the interface with the alloy substrate. Following the re-oxidation step, there is a 200nm chromia layer and a 400nm cubic spinel reaction layer (RL) between the alloy and the MCO. These layers thicken to 800nm and 1.2μm, respectively after 1000h oxidation. These observations are compared to our previous studies of MCO-coated Crofer 22 APU, and the implications for long-term SOFC performance are discussed.

The effect of alloy heat treatment on the oxidation kinetics and oxide scale microstructure of Crofer 22 APU has been studied. Parabolic oxidation rate constants were measured for the as-received alloy and after pre-oxidation heat treatment in argon at 1050 degrees C for 1 and 4 h. The oxide scale microstructure was investigated using scanning electron microscopy, focused ion beam milling and transmission electron microscopy. It was found that the alloy forms a two-layer scale with a continuous chromia layer and a discontinuous MnCr2O4 overlayer. Two forms of internal oxides were also formed: subscale pockets of spinet and isolated TiOx precipitates in the underlying alloy. The pre-oxidation heat treatment had a profound effect on the grain size and morphology of the Cr2O3 and MnCr2O4 layers in the scale. The heat-treated samples exhibit a 3.5x lower parabolic oxidation rate constant than the as-received Crofer 22 APU. This improvement in oxidation resistance is attributed to the dramatic differences in the morphology of the oxide scale that forms during the earliest stages of oxidation (<5 h). The implications of these findings for oxidation mechanisms and long-term SOFC performance are discussed. (C) 2013 United Technologies Corporation and Elsevier B.V. All rights reserved.

The microstructural development of Mn1.5Co1.5O4-coated Crofer22 APU has been studied using cross-sectional transmission electron microscopy. Alloy samples were coated via a slurry process involving consolidation by reduction and re-oxidation, and these samples were then oxidized at 800 degrees C for times of up to 1000 h. All samples exhibited a thin chromia scale at the alloy/coating interface plus spinel phases as a reaction layer between the chromia and the manganese cobaltite coating. The oxidized samples also exhibited pockets of stoichiometric MnCr2O4 spinel at the chromia/alloy interface and internal Ti-rich oxides in the alloy below the chromia. The reaction layer spinels exhibit remarkable changes in thickness, morphology and composition, and these effects are explained on the basis of changes in the diffusive fluxes during the different stages of coating application and subsequent exposure. The possible consequences of these observations for the degradation mechanisms that could affect SOFC interconnects produced from MCO-coated Crofer22 APU are discussed. (C) 2012 United Technologies Corporation. Published by Elsevier B.V. All rights reserved.

A systematic study and evaluation were performed on the effect of scandium doping at the B site of Pr0.6Sr0.4Co0.2Fe0.8O3−δ (PSCF) on key material properties as cathode for intermediate temperature solid oxide fuel cells (IT-SOFC). The doped products Pr0.6Sr0.4(Co0.2Fe0.8)(1−x)ScxO3−δ (PSCFSx, x=0.0–0.2) retained perovskite structure confirmed by X-ray diffraction, and their particles were smaller than the non-doped materials as evidenced by TEM. The electrical conductivity (EC) of PSCFSx decreased with increasing Sc3+ content, but EC values were still larger than 100 S cm−1 in temperature range of 300–800 °C as x ≤ 0.1. The thermal expansion coefficients (TEC) of PSCFSx were observed to generally decrease with increasing x especially at lower temperature range of 50–600 °C. In addition, the AC impedance revealed better electrochemical performance of PSCFSx cathode as x ≤ 0.1 than that of the undoped sample PSCF. Therefore, PSCFSx (x ≤ 0.1) shows some potential as cathode electrode for IT-SOFC. The function of Sc3+ dopant was tentatively elucidated and discussed.

Interaction of current collectors with coated interconnect alloys was examined using dual-coating specimens. Oxidation kinetics of (La,Sr)(Co,Fe)O3 (LSCF)/Mn1.5Co1.5O4 (MCO) and (La,Sr)(Mn)O3 (LSM)/MCO coated Haynes 230 (H230) was determined at 750°C in air via a gravimetric method. The LSCF/MCO dual coating samples exhibited a rate constant 2 times larger than that of the LSM/MCO coated H230. SrCrO4 that formed at the LSCF/MCO coated H230 interface contributed to the increased rate constant. No SrCrO4 was detected at the interface of the LSM/MCO coated H230. Chemical stability of LSCF in air at 750°C was confirmed by TGA. Area specific resistance (ASR) of MCO coated Haynes 230 (H230) and Crofer 22 APU with LSCF and LSM (coated H230 only) current collectors was measured at 800°C for 1100h. No gross difference in ASR evolution was observed between the LSCF/MCO-H230 and LSM/MCO-H230 assemblies. Activation energy of conduction of the LSCF/MCO-H230 and LSCF/MCO-Crofer 22 samples evolved from 0.63eV to 0.80eV and from 0.53eV to 0.63eV respectively over a period of ca. 1100h, suggesting somewhat different interface chemistry evolution. Sr transport was observed in the LSCF/MCO-H230 samples subjected to both exposure test and ASR measurement, whereas it was not detected on the LSCF/MCO-Crofer 22 sample. Mechanism of the Sr transport is discussed on a qualitative basis to account for the observations.

The present study focuses on the model-based conceptual design of utility-scale power generation systems with a power block comprising a Solid Oxide Fuel Cell (SOFC) and steam/gas turbine bottoming cycles. The design includes production of coal gas via coal gasification, coal gas clean-up process steps, as well as carbon capture technology downstream of the power block. Various options for system design configurations and operating parameters exist for such power plants. The current work focuses on a subset of these configurations that makes use of catalytic coal gasification, state-of-the-art gas turbine technology, and oxy-combustion for straightforward carbon separation. A library of first-principles component models for gasifier, SOFC, gas and steam turbines, and oxygen combustor as well as phenomenological models for the air separation unit and coal gas clean-up process were developed. System analyses of two atmospheric and a pressurized system concept will be presented. The three system configurations will be compared using system performance metrics. All systems meet the Solid State Energy Conversion Alliance (SECA) minimum requirements, i.e., produce ≥100 MW power with ≥50% electrical efficiency based on coal HHV and capture more than 90% of the carbon in the coal feedstock.

The oxidation behavior of Mn1.5Co1.5O4 (MCO)-coated Haynes 230 (H230) and Crofer 22 APU was investigated between 700 and 900 degrees C. The oxidation kinetics of the coated alloys was compared with that of base alloys at 800 degrees C. An apparent two-stage kinetics behavior of the MCO-coated Crofer 22 APU was observed. The coating effectively reduced the oxidation rate constants of Crofer 22 APU by 5.5 times, whereas it did not seem to affect the oxidation kinetics of H230. The oxidation activation energies of the coated alloys suggest distinctly different oxidation mechanisms between the coated H230 and Crofer 22 APU. A Cr-modified spinel was observed in the interface region between the metal oxide scale and the spinel coating after long-term oxidation for both alloys. A semiquantitative model of oxidation kinetics was developed to explain the different behaviors observed. Apparently, the Cr-modified spinel may play a more important role on H230 during long-term oxidation. The heat-treatment of H230 in the reducing environment used for the MCO coating application processes appeared to debit oxidation resistance of the base alloy. The optimization of the MCO application process is expected to benefit oxidation resistance as well as chromia containment on H230. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3391820] All rights reserved.