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Gas Turbines: Combustion, Fuels, and Emissions

# Aero-Thermodynamic Consideration of Single-Crystal-Silicon Premixed-Fuel Microscale Can Combustor

[+] Author and Article Information
Moriaki Namura1

Toshiyuki Toriyama

Department of Micro System Technology,  Ritsumeikan University, 1-1-1 NojiHigashi, Kusatsu, Shiga, 525-8577, Japan

In the estimation of Re on the basis of the burning velocity for the microscale combustor, we used the laminar burning velocity in Eq. 1. In the burning velocity model, the effect of the turbulence velocity $ST$ on the combustion efficiency may be represented as a function of the laminar burning velocity $SL$ multiplied by the a power of Re (i.e., $ST∝SLRea$ ) [13-14]. This concept was first proposed by Damköhler (NACA TM 1112, 1947). Re is also a function of the pressure loss in the chamber. For practical applications, however, the pressure loss related to $Rea$ is expected to be small and can be neglected. Therefore, we can estimate $ST$ as a function of pressure, i.e., $ST∝SL∝P3(n-2)/(n-2)nn$ (n is the order of the reaction) in Eq. 2. For further details, please refer to the original papers, Refs. [13-14].

1

Corresponding author.

J. Eng. Gas Turbines Power 134(7), 071501 (May 23, 2012) (11 pages) doi:10.1115/1.4006059 History: Received June 23, 2011; Revised January 24, 2012; Published May 23, 2012; Online May 23, 2012

## Abstract

This paper describes the aero-thermodynamic design, microfabrication and combustion test results for a single-crystal-silicon premixed-fuel microscale can combustor. The combustion chamber volume is 277 mm3 , and the microscale can combustor was fabricated by silicon bulk micromachining technology. Hydrogen fuel-air premixing was performed in the combustion test. The operation space in which stable combustion occurred was experimentally determined from the combustion temperature and efficiency for various mass flow rates and equivalence ratios. The expression for the combustion efficiency under conditions where the overall rate of heat release is limited by the chemical kinetics was consistent with the burning velocity model. The flame stabilization, the range of equivalence ratios and the maximum air velocity that the combustor can tolerate before flame extinction occurs were in agreement with the well - stirred reactor (WSR) and combustion loading parameter (CLP) models. A proposed aero-thermodynamic design approach based on these three models provides a physical interpretation of the experimental results in the operation space of stable combustion. Furthermore, this approach provides a unified physical interpretation of the stable combustion operation spaces of microscale combustors with various dimensions and configurations. Therefore, it is demonstrated that the proposed aero-thermodynamic approach has an important role in predicting the preliminary aerodynamic design performances of new microscale combustors.

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## Figures

Figure 1

Design chart for combustion efficiencies against relevant variables on the basis of burning velocity model (θ≡(P3)1.75Aref(Lref)0.75exp(T3/T3300300)m·A) [7]

Figure 2

Variation of geometrical boundary of recirculation zone for straight-hole flame holder

Figure 3

Geometrical structure of combustion flame and definition of control volume for calculation of Eqs. 5 to 8 (highly simplified)

Figure 4

Figure 5

Cross-sectional views of prototyped silicon microscale can combustor

Figure 6

Exploded view of micro-fabricated seven silicon wafers (silicon microstructures were fabricated by MEMS process)

Figure 7

Photograph of experimental setup for microscale can combustor and related instruments

Figure 8

Experimental measurements for combustor exit temperatures with the variation of equivalence ratio

Figure 9

Experimental measurements for combustor efficiencies with the variation of equivalence ratio

Figure 10

Comparison of prediction and experimental results for stable combustion operating space

Figure 11

Schematic of flame holder wake two dimensional flame structure (highly simplified)

Figure 12

Comparison of calculation and experimental values for characteristic chemical time used for flame extinction criteria

Figure 13

Experimental values of cooling effectiveness with the variation of flow fraction of coolant flow (state-of-the-art cooling technology for aircraft engine combustors were indicated as comparison)

Figure 14

Combustion inefficiency due to unused chemical energy with the variation of equivalence ratio

Figure 15

Correlation between combustion efficiencies for silicon microscale combustors and Lefebvre’s θ parameters (θ≡(P3)1.75Aref(Lref)0.75exp(T3/T3300300)m·A) [7]

Figure 16

Comparison of predictions and experimental results for stable combustion operating spaces obtained from past and present works (previous works were reported by MIT [1-4] and SIMTEC [8])

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