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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Low-Emission, Liquid Fuel Combustion System for Conventional and Alternative Fuels Developed by the Scaling Analysis

[+] Author and Article Information
Yonas Niguse

Department of Mechanical Engineering,
The University of Alabama,
Tuscaloosa, AL 35487
e-mail: ygniguse@crimson.ua.edu

Ajay Agrawal

Department of Mechanical Engineering,
The University of Alabama,
Tuscaloosa, AL 35487
e-mail: AAgrawal@eng.ua.edu

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2015; final manuscript received August 27, 2015; published online October 13, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(4), 041502 (Oct 13, 2015) (11 pages) Paper No: GTP-15-1307; doi: 10.1115/1.4031475 History: Received July 14, 2015; Revised August 27, 2015

The objective of this study is to develop a theoretical basis for scalability considerations and design of a large-scale combustor utilizing flow blurring (FB) atomization. FB atomization is a recently discovered twin-fluid atomization concept, reported to produce fine spray of liquids with wide range of viscosities. Previously, we have developed and investigated a small-scale swirl-stabilized combustor of 7-kWth capacity. Spray measurements have shown that the FB injector's atomization capability is superior when compared to other techniques, such as air blast atomization. However, despite these favorable results, scalability of the FB injector and associated combustor design has never been explored for large capacity; for example, for gas turbine applications. In this study, a number of dimensionless scaling parameters that affect the processes of atomization, fuel–air mixing, and combustion are analyzed, and scaling criteria for the different components of the combustion system are selected. Constant velocity criterion is used to scale key geometric components of the system. Scaling of the nonlinear dimensions and complex geometries, such as swirler vanes and internal parts of the injector is undertaken through phenomenological analysis of the flow processes associated with the scaled component. A scaled-up 60-kWth capacity combustor with FB injector is developed and investigated for combustion performance using diesel and vegetable oil (VO) (soybean oil) as fuels. Results show that the scaled-up injector's performance is comparable to the smaller scale system in terms of flame quality, emission levels, and static flame stability. Visual flame images at different atomizing air-to-liquid ratio by mass (ALR) show mainly blue flames, especially for ALR > 2.8. Emission measurements show a general trend of lower CO and NOx levels at higher ALRs, replicating the performance of the small-scale combustion system. Flame liftoff height at different ALRs is similar for both scales. The scaled-up combustor with FB injector preformed robustly with uncompromised stability for the range of firing rates (FRs) above 50% of the design capacity. Experimental results corroborate with the scaling methodology developed in this research.

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Figures

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Fig. 1

Schematic illustration of flow-blurring atomization

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Fig. 2

Schematic of the swirl stabilized dual-fuel burner setup

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Fig. 3

Schematic representation of atomization, mixing, and combustion processes

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Fig. 4

Schematic diagram of scaled-up parts of the burner and the injector

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Fig. 5

Geometrical representation of swirler

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Fig. 6

Photographs of the small (left) and scaled-up (right) inlet swirlers

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Fig. 7

Schematic diagram of experimental setup

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Fig. 8

Flame photographs of diesel combustion for different ALR (HRR: 54 kW, dimensions in cm)

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Fig. 9

Plots of experimental flame and calculated and lift heights for diesel and different ALR

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Fig. 10

Radial profiles of (a) CO and (b) NOx emissions for diesel for different ALRs, for the small-scale and large-scale systems

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Fig. 11

Radial profiles of CO (a) and NOx (b) for diesel combustion at ALR of 2.8 for heat release rates of 45 and 54 kW

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Fig. 12

Flame photographs of VO combustion for different ALR (HRR: 54 kW, dimensions in cm)

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Fig. 13

Plots of experimental and calculated flame liftoff heights for VO and different ALR

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Fig. 14

Radial profiles of (a) CO and (b) NOx emissions for VO for different ALRs, for the small-scale and large-scale systems

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