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

Shockless Explosion Combustion: Experimental Investigation of a New Approximate Constant Volume Combustion Process

[+] Author and Article Information
Thoralf G. Reichel

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Berlin 10623, Germany
e-mail: thoralf.reichel@tu-berlin.de

Jan-Simon Schäpel, Rudibert King

Chair of Measurement and Control,
Technische Universität Berlin,
Berlin 10623, Germany

Bernhard C. Bobusch, Christian Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Berlin 10623, Germany

Rupert Klein

Department of Mathematics,
Geophysical Fluid Dynamics,
Freie Universität Berlin,
Berlin 14195, Germany

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 June 21, 2016; final manuscript received June 23, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 021504 (Sep 13, 2016) (7 pages) Paper No: GTP-16-1257; doi: 10.1115/1.4034214 History: Received June 21, 2016; Revised June 23, 2016

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches such as pulsed detonation combustion. The combustion is controlled via the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous auto-ignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the auto-ignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2 Hz. Application of OH*– and dynamic pressure sensors allows for a spatially and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable auto-ignition already at 920 K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the auto-ignition.

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References

Figures

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Fig. 1

Ideal cycle comparison for constant volume combustion (Humphrey) and constant pressure combustion (Joule): T-S diagram (left); efficiency over pressure ratio (right); from Ref. [1]

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Fig. 2

Schematic of the SEC cycle

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Fig. 3

Effect of equivalence ratio stratification on ignition delay time distribution

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Fig. 4

Schematic of the atmospheric SEC test rig

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Fig. 5

Section view of the inlet section with the fluidic diode and fuel injection ring which applies fluidic oscillators

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Fig. 6

Diagnostics of the combustion test rig

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Fig. 7

Identification experiment: (a) Fuel concentration and (b) valve input: five random amplitude sequences

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Fig. 8

Cross-validation experiment: (a) Fuel concentration and (b) valve input: five random amplitude sequences

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Fig. 9

Example of timing sequence for main air, fuel, and PMT sensor readings over one ignition cycle, amplitudes are arbitrarily chosen

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Fig. 10

ILC: convergence speed of the control error

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Fig. 11

Converged ILC after 100 iterations: (a) Fuel concentration compared to the reference and (b) valve input generated by the ILC

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Fig. 12

Starting condition for the ILC (solid/crosses) and converged ILC after 500 iterations (dashed/cirles). (a) ignition time compared to the reference and (b) valve input generated by the ILC.

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Fig. 13

ILC: Variance of the detected ignition times (thin line) and its moving average (thick line)

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