In the present work, the proportion of carbon monoxide to hydrogen is widely varied to simulate different compositions of synthesis gas and the potential of the fuel mixture to excite combustion oscillations in a laboratory-scale turbulent bluff body combustor is investigated. The effect of parameters such as the bluff body location and equivalence ratio on the selfexcited acoustic oscillations of the combustor is studied. The flame oscillations are mapped by means of simultaneous highspeed CH and OH chemiluminescence imaging along with dynamic pressure measurement. Mode shifts are observed as the bluff body location or the air flow Reynolds number/overall equivalence ratio are varied for different fuel compositions. It is observed that the fuel mixtures that are hydrogen-rich excite high amplitude pressure oscillations as compared to other fuel composition cases. Higher H2 content in the mixture is also capable of exciting significantly higher natural acoustic modes of the combustor so long as CO is present, but not without the latter. The interchangeability factor Wobbe Index is not entirely sufficient to understand the unsteady flame response to the chemical composition. Copyright © 2017 ASME.

Satyanarayanan R. Chakravarthy

Department of Aerospace Engineering

Nikhil Ashokbhai Baraiya

Baladandayuthapani Nagarajan

carbon

carbon monoxide

combustion

Fuels

Mixtures

Reynolds number

Synthesis gas

Turbomachinery

Chemical compositions

COMBUSTION OSCILLATION

DYNAMIC PRESSURE MEASUREMENTS

EFFECT OF PARAMETERS

Experimental investigations

OH CHEMILUMINESCENCE

PRESSURE OSCILLATION

UNSTEADY FLAME RESPONSE

Combustors

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Experimental Investigation of Combustion Dynamics in a Turbulent Syngas Combustor

Proceedings of the ASME Turbo Expo

A laboratory-scale bluff body combustor is mapped for its stability and flame dynamics of non-premixed flames with three fuels, namely, pure H2, H2[sbnd]CH4 mixture, and H2[sbnd]CO mixture, the last one representing syngas. Unsteady pressure measurements and high-speed OH* and CH*/CO2* chemiluminescence imaging are simultaneously performed. The combustor behaviour with syngas is markedly different than the other two in exciting high frequency oscillations, typically at the third harmonic longitudinal acoustic mode of the duct at high air flow Reynolds numbers (Re). In contrast, the H2[sbnd]CH4 excites only the fundamental longitudinal mode, and pure H2 excites up to the first harmonic. The latter two are observed to lock on to the shear layer mode of the bluff body wake, whereas the H2[sbnd]CO case locks on to thrice the Strouhal number associated with the shear layer mode, commensurate with the excitation of the third harmonic natural acoustic mode. Time-averaged OH* and CO2* chemiluminescence images show large-scale structure for the H2[sbnd]CH4 case compared to heat release rate zones aligned with the shear layer in the pure H2 and H2[sbnd]CO cases. Cross-sectionally averaged chemiluminescence profiles exhibit a streamwise stagger in the peaks of OH* and CO2*, suggesting two heat release rate zones, that could excite the acoustic oscillations. The instantaneous profiles indicate a convective delay between the two heat release rate zones that is close to the third harmonic acoustic time scale. The sequential of H2 oxidation to OH followed by CO oxidation by OH to form CO2 are considered to be responsible for the high frequency excitation in the case with the H2[sbnd]CO mixture when compared to the other two cases. © 2019 Hydrogen Energy Publications LLC

International Journal of Hydrogen Energy

Excitation of high frequency thermoacoustic oscillations by syngas in a non-premixed bluff body combustor

An experimental investigation on the effect of syngas composition (H 2 /CO) on thermodynamic instability of a bluff-body combustor is studied. Three syngas compositions, namely, 25%H 2 –75%CO, 50%H 2 –50%CO and 75%H 2 –25%CO, and pure hydrogen and 75%H 2 –25%CH 4 are acoustically characterized by varying the inlet Reynolds number, Re, in the range of 2200–8100. The combustor is observed to undergo two modes of thermo-acoustic instability across the above Re range for all syngas compositions and pure hydrogen, whereas for the H 2 –CH 4 composition, the instability manifests at a single frequency ∼130 Hz. For all the syngas compositions, the pressure oscillations exhibit low frequency (130 Hz) at low Re, and bifurcate to higher frequency (∼500 Hz) at mid-range Re values, while pure hydrogen exhibits bifurcation from the low frequency to the first harmonic (∼260 Hz). The high frequency observed with the syngas compositions is at the third harmonic natural acoustic mode of the combustor and matches thrice the Strouhal frequency of the hydrodynamic oscillations of the shear layer separating from the bluff body. Further investigation into the nature of the dynamic behaviour across the listed fuels is performed using simultaneous time resolved imaging of OH* and CO 2 * chemiluminescence and two-component particle image velocimetry. The peak in the CO 2 * chemiluminescent intensity is found to be axially staggered downstream of that of OH*. This is due to sequential oxidation of H 2 and CO, the former producing OH as an intermediate consumed by the latter. Spatio-temporal analysis of the time-resolved data reveals that the presence of the flame in the shear layer of the bluff-body plays a significant role in modulating the high frequency acoustic excitation. Further, a spatial Rayleigh map is derived based on both the OH* and CO 2 * chemiluminescence, which reveals the bluff-body shear layer dynamics to yield the key driving and damping regions in the present study. © 2019 Hydrogen Energy Publications LLC

Effect of syngas composition on high frequency combustion instability in a non-premixed turbulent combustor

A combustor with a divergent inlet passage and a coaxially movable bluff-body flame holder has been developed to enable self-excitation of high-amplitude acoustic oscillations, for the purpose of enhancing the rate of evaporation of water sprays. Commercially available liquid petroleum gas is used as fuel. The acoustic pressure levels and modal contents are controlled by varying the location of the bluff body along the axis of the combustor relative to its inlet. Locating the bluff body closer to the inlet yields higher acoustic pressure amplitudes over a wider range of fuel-air ratios. The excitation of high amplitudes is accompanied by a shift from the fundamental to the first harmonic at different fuel-air ratios for different air mass flow rates in the fuel-lean range. When high sound pressure levels are excited in the combustor, the heat transfer due to water cooling of the combustor walls and across the walls of the tailpipe increase considerably, up to 40% for an increase in sound pressure levels from 145 to 160 dB. Water-spray evaporation experiments are performed with low and high sound pressure levels of acoustic excitation for different water injection rates over a range of mass flow rates of fuel and air. For a given mass flow rate of air and fuel, it is found that the water evaporation rate increases significantly above a certain threshold acoustic pressure, up to 107 % for a sound pressure level of 156 dB, despite the considerable increase in heat loss due to the acoustic oscillations.

Journal of Propulsion and Power

Characterization of an acoustically self-excited combustor for spray evaporation

Combustion instability characteristics of H2/CO/CH4 syngases and synthetic natural gases in a partially-premixed gas turbine combustor: Part I—Frequency and mode analysis

Combustion and Flame

On the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitions

Combustion Science and Technology

Velocity and Flame Wrinkling Characteristics of a Transversely Forced, Bluff-Body Stabilized Flame, Part I: Experiments and Data Analysis

Volume 2: Combustion, Fuels and Emissions, Parts A and B

Experimental Investigations of Flame Stabilization of a Gas Turbine Combustor

Experimental investigation of combustion dynamics in a turbulent syngas combustor

Journal	Proceedings of the ASME Turbo Expo
Publisher	American Society of Mechanical Engineers (ASME)
Open Access	No