Title

MICRO-TUBULAR FLAME-ASSISTED FUEL CELL FUNDAMENTALS AND APPLICATIONS IN MICRO COGENERATION

Date of Award

June 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jeongmin Ahn

Subject Categories

Engineering

Abstract

An innovative concept for using Solid Oxide Fuel Cell (SOFC) technology to power a gas-fired residential furnace is evaluated, including fundamental research targeted to enable new applications. The Flame-assisted Fuel Cell (FFC) concept is envisioned to address known deficiencies of the Direct Flame Fuel Cell (DFFC), which has a simple no-chamber setup and has shown promise for direct use of hydrocarbons, rapid startup, and rapid thermal cycling, but has suffered from low power density, lower electrical efficiency, soot formation and carbon deposition. The FFC concept is a modification to the conventional DFFC setup that places the SOFC in the combustion exhaust in a dual chamber SOFC configuration. In this study, a micro-Tubular SOFC (mT-SOFC) is utilized, which has demonstrated advantages of rapid startup and rapid thermal cycling. The main purposes of this study are: 1) develop a mT-SOFC that improves the power density, electrical efficiency and thermal cycling resistance for use in the FFC setup; 2) investigate the combustion exhaust composition, especially H2 and CO, of different fuels at fuel-rich premixed combustion conditions; 3) develop a micro-tubular FFC (mT-FFC) that operates with hydrocarbons directly while offering rapid startup, rapid thermal cycling, high power density, high electrical efficiency, no soot formation, and high carbon deposition resistance.

To improve the mT-SOFC power density, the thickness of the doped-ceria (Sm0.20Ce0.80O2-δ and Gd0.10Ce0.90O1.95) buffer layer is investigated to prevent Sr and Zr interdiffusion at the electrolyte/cathode interface. The exhaust species from CH4 and C3H8 combustion in air are investigated. A mT-FFC is investigated at different fuel-rich combustion conditions using a model combustion exhaust to assess the effect of equivalence ratio, temperature, and flow rate on open circuit voltage, polarization, power density and fuel utilization. A mT-FFC stack design is developed and integrated with a novel two-stage combustor which is denoted a Rich-burn, Flame-assisted Fuel Cell, Quick-mix, Lean-burn (RFQL) combustor for micro Combined Heat and Power (mCHP) applications. The RFQL system is investigated for polarization, power density, electrical efficiency and thermal cycling characteristics. A mT-FFC stack is thermal cycled 3,000 times at high heating and cooling rates with low degradation reported. Theoretical derivation of a maximum electrical efficiency limit is presented. Methods used to assess current fuel cell mCHP is investigated and proper methods for assessing mT-FFC mCHP are discussed.

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