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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Catalytic Combustion Systems for Microscale Gas Turbine Engines

[+] Author and Article Information

Center for Micro and Nano Technology, Lawrence Livermore National Laboratory, Livermore, CA 94551

J. Peck, I. A. Waitz

Gas Turbine Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139

J. Eng. Gas Turbines Power 129(1), 49-60 (Sep 28, 2005) (12 pages) doi:10.1115/1.2204980 History: Received August 25, 2005; Revised September 28, 2005

Abstract

As part of an ongoing effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, modeling, and experimental assessment of a catalytic combustion system. Previous work has indicated that homogenous gas-phase microcombustors are severely limited by chemical reaction timescales. Storable hydrocarbon fuels, such as propane, have been shown to blow out well below the desired mass flow rate per unit volume. Heterogeneous catalytic combustion has been identified as a possible improvement. Surface catalysis can increase hydrocarbon-air reaction rates, improve ignition characteristics, and broaden stability limits. Several radial inflow combustors were micromachined from silicon wafers using deep reactive ion etching and aligned fusion wafer bonding. The $191mm3$ combustion chambers were filled with platinum-coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures of $1100K$ were achieved at mass flow rates in excess of $0.35g∕s$. This corresponds to a power density of $∼1200MW∕m3$; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion in a similar geometry. Low-order models, including time-scale analyses and a one-dimensional steady-state plug-flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables.

Figures

Figure 1

Baseline engine schematic

Figure 2

Schematic (a) and SEM (b) of six-wafer microcombustor

Figure 3

Comparison of hydrogen and propane gas-phase performance

Figure 4

Schematic of microcombustor showing location of catalyst material

Figure 5

Photograph (a) and SEM (b) of 95% porous nickel foam substrate

Figure 6

Photograph (a) and SEM (b) of 88.5% porous FeCrAlY foam substrate

Figure 7

Photograph (a) and SEM (b) of 78% porous Inconel-625 foam substrate

Figure 8

Fully packaged microcombustor

Figure 9

Ignition characteristics for catalytic microcombustors

Figure 10

Exit gas temperature for microcombustor with noncatalytic foam

Figure 11

Exit gas temperature plot comparing Ni-Pt and FeCrAlY-Pt devices for ϕ=1

Figure 12

Overall combustor efficiency plot comparing Ni-Pt and FeCrAlY-Pt devices for ϕ=1

Figure 13

Efficiency breakdown for catalytic microcombustor with Ni-Pt, ϕ=1.0

Figure 14

Total pressure loss plot comparing Ni-Pt and FeCrAlY devices for ϕ=1

Figure 15

Pressure loss versus mass flow rate for porous media, comparing estimates from Eq. 13 and experimental data

Figure 16

Peclet number versus diameter

Figure 17

Axial temperature profile in porous media plug flow reactor

Figure 18

Axial fuel concentration profile in porous media plug flow reactor

Figure 19

Comparison of model to experiment

Figure 20

Fuel conversion profiles for various surface area-to-volume ratios

Figure 21

Operating space for catalytic microcombustor; lines of constant power density

Figure 22

Nondimensional operating space; Peclet number versus thermal efficiency

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