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1

Numerical study of laminar non-premixed biogas-air flames behind backward facing steps

Harish Alagani, Raghavan Vasudevan

Archive of Mechanical Engineering

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2022

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LXIX, nr 2

221–-244

EN

Biogas, a renewable fuel, has low operational stability range in burners due to its inherent carbon-dioxide content. In cross-flow configuration, biogas is injected from a horizontal injector and air is supplied in an orthogonal direction to the fuel flow. To increase the stable operating regime, backward facing steps are used. Systematic numerical simulations of these flames are reported here. The comprehensive numer- ical model incorporates a chemical kinetic mechanism having 25 species and 121 elementary reactions, multicomponent diffusion, variable thermo-physical properties, and optically thin approximation based volumetric radiation model. The model is able to predict different stable flame types formed behind the step under different air and fuel flow rates, comparable to experimental predictions. Predicted flow, species, and temperature fields in the flames within the stable operating regime, revealing their anchoring positions relative to the rear face of the backward facing step, which are difficult to be measured experimentally, have been presented in detail. Resultant flow field behind a backward facing step under chemically reactive condition is compared against the flow fields under isothermal and non-reactive conditions to reveal the sig- nificant change the chemical reaction produces. Effects of step height and step location relative to the fuel injector are also presented.

2

Numerical analysis of structure, stability and entropy generation in biogas coflow diffusion flames

Kumar R. Nivethana, Kumaran S. Muthu, Raghavan Vasudevan

Archive of Mechanical Engineering

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2022

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LXIX, nr 1

99--128

EN

Biogas is a gaseous biofuel predominantly composed of methane and carbon-dioxide. Stability of biogas flames strongly depend upon the amount of carbon-dioxide present in biogas, which varies with the source of biomass and reactor. In this paper, a comprehensive study on the stability and flame characteristics of coflow biogas diffusion flames is reported. Numerical simulations are carried out using reactive flow module in OpenFOAM, incorporated with variable thermophysical properties, Fick’s and Soret diffusion, and short chemical kinetics mechanism. Effects of carbon-dioxide content in the biogas, temperatures of the fuel or coflowing air streams (preheated reactant) and hydrogen addition to fuel or air streams are analyzed. Entropy generation in these flames is also predicted. Results show that the flame temperature increases with the degree of preheat of reactants and the flames show better stability with the preheated air stream. Preheating the air contributes to increased flame stability and also to a significant decrease in entropy generation. Hydrogen addition, contributing to the same power rating, is seen to be relatively more effective in increasing the flame stability when added to the fuel stream. Results in terms of flow, temperature, species and entropy fields, are used to describe the stability and flame characteristics.

3

Spalanie gazów ziemnych niskokalorycznych w turbinach gazowych

Ślefarski R., Dobski T., Grzymisławski P, Gołębiewski M.

Rynek Energii

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2014

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Nr 2

54--60

PL

Artykuł przedstawia wyniki badań spalania gazów ziemnych niskokalorycznych LCNG - Low Calorific Natural Gases - w warunkach jakie panują w turbinach gazowych, za wyjątkiem ciśnienia, gdyż większość badań została wykonana dla ciśnienia otoczenia. Gazy LCNG mają podobne właściwości do gazów niekonwencjonalnych: uwięzionych i łupkowych. Stwierdzono, że spalanie gazów LCNG, zawierających nawet 50% azotu jest możliwe z puntu widzenia głównych parametrów pracy turbin: sprawności termodynamicznej, stabilności płomienia oraz emisji związków toksycznych NOx i CO. Parametry pracy są nawet lepsze niż turbin zasilanych gazami ziemnymi wysokometanowymi typu E, pod warunkiem dobrego zaprojektowania palników gazowych. Zasadniczo spalanie gazów LCNG powinno przebiegać w przepływie z silnym zawirowaniem, jednak stopień zawirowania, określony liczbą wirową S powinien być optymalnie dobrany do udziału molowego azotu w gazie. Wyniki badań i obliczeń zostały uzupełnione badaniami i oceną danych z elektrociepłowni wyposażonych w turbiny gazowe zasilane gazami ziemnymi niskokalorycznymi.

EN

Paper presents results of investigation combustion of natural gases- LCNG - Low Calorific Natural Gases - in the conditions as those used in a gas turbine, with the exception of the pressure, since most studies has been done for ambient pressure. LCNG gases have similar properties to the unconventional tight and shale gases. It has been found that the combustion LCNG gas containing 50% nitrogen as possible from the point of view of the main parameters of the gas turbine thermodynamic efficiency, flame stability and emission of pollutants: NOx and CO. Parameters are even better than the gas-powered turbines with H-Gas, on condition a good design of the gas burners. Essentially combustion gases LCNG should proceed in the flow with strong swirl, however, the degree of turbulence – particularly the swirl number S defined to be optimally selected for the mole fraction of nitrogen in the gas. Test results and calculations have been completed research and evaluation of data from power plants equipped with gas turbines powered by gas low-calorific natural gases.

4

Stabilizacja spalania rozpylonej strugi paliwa w wysokonapięciowym kanale plazmowym

Brzeziński H., Mączka T

Przegląd Elektrotechniczny

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2014

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R. 90, nr 10

53-56

PL

Przedstawiono wyniki prób stabilizacji płomienia podczas spalania rozpylonej strugi paliwa przy pomocy wysokonapięciowej plazmy łukowej o mocy do 170 VA. Badania wykonano na stanowisku laboratoryjnym wyposażonym w komercyjny palnik olejowy. Analizowano wpływ działania plazmy łukowej na jakość spalania oleju opałowego (stabilizacja płomienia, temperatury procesu i zawartość CO w spalinach w funkcji współczynnika nadmiaru powietrza λ). Sprawdzono możliwość „sztucznego” (λ >> 1) utrzymywania płomienia, dzięki plazmowej stabilizacji.

EN

Results of the flame stabilization during combustion of sprayed fuel by a high voltage plasma arc with power up to 170 VA, were presented. The study was performed on test stand equipped with a commercial oil burner. The influence of plasma arc activities on the quality of fuel oil combustion (the flame stabilization, process temperature and CO content in the exhaust gas as the function of excess air ratio λ) were analyzed. Possibility of "artificial" (λ >> 1) maintenance of the flame by effect of plasma stabilization was verified.