Swirl and Pressure Effects on Colorless Distributed Combustion for Gas Turbine Application

2011 ◽  
Author(s):  
Ahmed Khalil ◽  
Vaibhav Arghode ◽  
Ashwani Gupta
Keyword(s):  
Gas Turbine ◽  
Pressure Effects ◽  
Colorless Distributed Combustion

scholarly journals Experimental and Theoretical Study of Droplet Vaporization in a High Pressure Environment

1997 ◽  
Author(s):  
Jörg Stengele ◽  
Michael Willmann ◽  
Sigmar Wittig
Keyword(s):  
High Pressure ◽  
Gas Turbine ◽  
Droplet Diameter ◽  
Droplet Evaporation ◽  
Pressure Effects ◽  
Evaporation Process ◽  
Temperature Model ◽  
Uniform Temperature ◽  
Continuous Increase ◽  
Limit Model

Due to the continuous increase of pressure ratios in modern gas turbine engines the understanding of high pressure effects on the droplet evaporation process gained significant importance. The precise prediction of the evaporation time and the movement of the droplets is crucial for optimum design and performance of modern gas turbine combustion chambers. Numerous experimental and numerical investigations have been done already in order to understand the evaporation process of droplets in high pressure environments. But until now, all high pressure experiments were carried out with droplets attached to a thin fiber resulting in the impairment of the droplet evaporation process due to the suspension unit. In the present study, a new experimental set up is introduced where the evaporation of free falling droplets is investigated. Monodisperse droplets are generated in the upper part of the test rig and fall through the stagnant high pressure gas inside the pressure chamber. Due to the relative velocity between droplet and gas, convective effects have to be considered in this study which are taken into account by experimental correlations. The droplet diameter and the droplet velocity are measured simultaneously by means of video technique and a stroboscope lamp. Detailed measurements with heptane droplets are presented for different pressures (p = 20 bar, 30 bar and 40 bar), gas temperatures (T = 550 K and 650 K) and initial diameters (d0 = 680 μm, 780 μm and 840 μm). The experiments were carried out with single component droplets. The experimental results are compared with numerical calculations. For this a theoretical model was developed based on the Conduction Limit model and the Uniform Temperature model. Good agreement for all conditions investigated is observed when using the Conduction Limit model. The Uniform Temperature model predicts incorrectly the evaporation process of the droplet.

Multicomponent and High-Pressure Effects on Droplet Vaporization

2002 ◽  
Vol 124 (2) ◽  
pp. 248-255 ◽  
Author(s):  
S. K. Aggarwal ◽  
H. C. Mongia
Keyword(s):  
High Pressure ◽  
Gas Turbine ◽  
Single Component ◽  
Pressure Effects ◽  
Diffusion Limit ◽  
Fuel Droplet ◽  
Droplet Model ◽  
Droplet Vaporization ◽  
Wide Range ◽  
High Pressure Effects

This paper deals with the multicomponent nature of gas turbine fuels under high-pressure conditions. The study is motivated by the consideration that the droplet submodels that are currently employed in spray codes for predicting gas turbine combustor flows do not adequately incorporate the multicomponent fuel and high-pressure effects. The quasi-steady multicomponent droplet model has been employed to investigate conditions under which the vaporization behavior of a multicomponent fuel droplet can be represented by a surrogate pure fuel droplet. The physical system considered is that of a multicomponent fuel droplet undergoing quasi-steady vaporization in an environment characterized by its temperature, pressure, and composition. Using different vaporization models, such as infinite-diffusion and diffusion-limit models, the predicted vaporization history and other relevant properties of a bicomponent droplet are compared with those of a surrogate single-component fuel droplet over a range of parameters relevant to gas turbine combustors. Results indicate that for moderate and high-power operation, a suitably selected single-component (50 percent boiling point) fuel can be used to represent the vaporization behavior of a bicomponent fuel, provided one employs the diffusion-limit or effective-diffusivity model. Simulation of the bicomponent fuel by a surrogate fuel becomes increasingly better at higher pressures. In fact, the droplet vaporization behavior at higher pressures is observed to be more sensitive to droplet heating models rather than to liquid fuel composition. This can be attributed to increase in the droplet heatup time and reduction in the volatility differential between the constituent fuels at higher pressures. For ignition, lean blowout and idle operations, characterized by low pressure and temperature ambient, the multicomponent fuel evaporation cannot be simulated by a single-component fuel. The validity of a quasi-steady high-pressure droplet vaporization model has also been examined. The model includes the nonideal gas behavior, liquid-phase solubility of gases, and variable thermo-transport properties including their dependence on pressure. Predictions of the high-pressure droplet model show good agreement with the available experimental data over a wide range of pressures, implying that quasi-steady vaporization model can be used at pressures up to the fuel critical pressure.

scholarly journals A Computational Study of Pressure Effects on Pollutants Generation in Gas Turbine Combustors

1995 ◽  
Author(s):  
E. M. Amin ◽  
G. E. Andrews ◽  
M. Pourkashnian ◽  
A. Williams ◽  
R. A. Yetter
Keyword(s):  
Gas Turbine ◽  
Mass Fraction ◽  
Soot Formation ◽  
Numerical Study ◽  
Computational Study ◽  
Mixture Fraction ◽  
Gaussian Function ◽  
Soot Oxidation ◽  
Major Effect ◽  
Pressure Effects

A numerical study of the effect of pressure on the formation of NOx and soot in an axisymmetric 30° counter rotating axial swirler lean low NOx gas turbine combustor has been conducted. This has previously been studied experimentally and this CFD investigation was undertaken to explain the higher than expected NOx emissions. The combustion conditions selected for the present study were 300 deg K inlet air, 0.4 overall equivalence ratio, and pressures of 1 and 10 bar. The numerical model used here involved the solution of time-averaged governing equations using an elliptic flow-field solver. The turbulence was modelled using algebraic stress modelling (ASM), The Thermo-chemical model was based on the laminar flamelet formulation. The conserved scalar/assumed pdf approach was used to model the turbulence chemistry interaction. The study was for two pressure cases at 1 and 10 bar. The turbulence-chemistry interaction is closed by assumption of a Clipped Gaussian function form for the fluctuations in the mixture fraction. The kinetic calculations were done separately from the flowfield solver using an opposed laminar diffusion flame code of SANDIA. The temperature and species profiles were made available to the computations through look-up tables. The pollutants studied in this work were soot and NO for which three more additional transport equations are required namely; averaged soot mass fraction, averaged soot particle number density, and finally averaged NO mass fraction. Soot oxidation was modelled using molecular oxygen only and a strong influence of pressure was predicted. Pressure was shown to have a major effect on soot formation.

Non-Premixed and Premixed Colorless Distributed Combustion for Gas Turbine Application

2010 ◽  
Author(s):  
Vaibhav Arghode ◽  
Ashwani K. Gupta
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Premixed Combustion ◽  
Spontaneous Ignition ◽  
Combustion Mode ◽  
Acoustic Signatures ◽  
Combustion Modes ◽  
Sound Levels ◽  
Colorless Distributed Combustion ◽  
Gas Recirculation

Non-premixed and premixed modes of Colorless Distributed Combustion (CDC) are investigated for application to gas turbine combustors. The CDC provides significant improvement in pattern factor, reduced NOx emission uniform thermal field in the entire combustion zone for it to be called as a isothermal reactor, and lower sound levels. Basic requirement for CDC is mixture preparation through good mixing between the combustion air and product gases so that the reactants are at much higher temperature to result in hot and diluted oxidant stream at temperatures that are high enough to auto-ignite the fuel and oxidant mixture. With desirable conditions one can achieve spontaneous ignition of the fuel with distributed combustion reactions. Distributed reactions can also be achieved in premixed mode of operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation two non-premixed combustion modes and one premixed combustion mode that provide potential for CDC is examined. In all the configurations the air injection port is positioned at the opposite end of the combustor exit, whereas the location of fuel injection ports is changed to give different configurations. The results are compared for global flame signatures, exhaust emissions, acoustic signatures, and radical emissions using experiments and flow field, gas recirculation and mixing using numerical simulations. Ultra low NOx emissions are observed for both the premixed and non-premixed combustion modes, and almost colorless flames (no visible flame color) have been observed for the premixed combustion mode. The non-premixed mode was also provided near colorless distributed combustion. The reaction zone is observed to be significantly different in the two non-premixed modes.

Atmospheric Tests of a Variable Combustor Geometry for Reducing Gas Turbine Emissions

1975 ◽  
Vol 97 (3) ◽  
pp. 327-333 ◽  
Author(s):  
J. A. Saintsbury ◽  
P. Sampath
Keyword(s):  
Gas Turbine ◽  
Reverse Flow ◽  
Full Range ◽  
Combustion Efficiency ◽  
Pressure Effects ◽  
Gas Turbine Combustor ◽  
Reducing Gas ◽  
Good Potential ◽  
Visualization Techniques ◽  
Full Simulation

Current concern with reduction of pollution from combustion systems resulted in a research program being undertaken to evaluate the potential of variable combustor geometry for reducing emissions from an annular reverse flow gas turbine combustor. A device which simulated a variable baffle in the annulus surrounding the combustor was investigated. Results indicated a good potential for this approach, if the combustor was specially developed for low emissions. The fluid dynamics of this concept were investigated in a model using flow visualization techniques. The hot tests under this program were carried out at atmospheric pressure with full simulation of combustor flows. Significant reductions in emissions and corresponding improvements in combustion efficiency were observed when a baffle was incorporated in the combustion system. It is recognized that all important pressure effects are absent in this work, but a subsequent program is planned to demonstrate the variable geometry concept on an engine over a full range of operation.

Colorless Distributed Combustion (CDC) With Swirl for Gas Turbine Application

2010 ◽  
Author(s):  
Ahmed E. E. Khalil ◽  
Vaibhav K. Arghode ◽  
Ashwani K. Gupta
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Hot Spot ◽  
Stability Limit ◽  
High Heat ◽  
Experimental Investigations ◽  
Gas Turbine Combustor ◽  
Swirl Flows ◽  
Thermal Nox ◽  
Colorless Distributed Combustion

Colorless Distributed Combustion (CDC) can provide significant improvement in gas turbine combustor performance. CDC is characterized by uniform thermal field in the entire combustion chamber, thus avoiding hot-spot regions for low NOx emissions (thermal NOx) and significantly improved pattern factor. In this paper, colorless distributed combustion with swirl is investigated in detail to seek the beneficial aspects of CDC and swirl flows with focus on developing ultra low emissions of NO and CO, and much improved pattern factor. Experimental investigations have been performed using a cylindrical combustor with different modes of fuel injection, swirling air injection and gas exit stream location of the combustor. Air was injected tangentially to impart swirl to the flow inside the combustor. Results showed very low levels of NO (∼3PPM) and CO (∼70PPM) emissions at equivalence ratio of 0.7 at a high heat release intensity of 36MW/m3atm with non-premixed mode of combustion. Results have also been obtained on lean stability limit and OH* chemiluminescence under both premixed and non-premixed conditions.

A Computational Study of Pressure Effects on Pollutant Generation in Gas Turbine Combustors

1997 ◽  
Vol 119 (1) ◽  
pp. 76-83 ◽  
Author(s):  
E. M. Amin ◽  
G. E. Andrews ◽  
M. Pourkashnian ◽  
A. Williams ◽  
R. A. Yetter
Keyword(s):  
Gas Turbine ◽  
Mass Fraction ◽  
Soot Formation ◽  
Laminar Flame ◽  
Numerical Study ◽  
Computational Study ◽  
Mixture Fraction ◽  
Gaussian Function ◽  
Soot Oxidation ◽  
Pressure Effects

A numerical study of the effect of pressure on the formation of NOx and soot in an axisymmetric 30 deg counterrotating axial swirler lean low-NOx gas turbine combustor has been conducted. This has previously been studied experimentally and this CFD investigation was undertaken to explain the higher than expected NOx emissions. The combustion conditions selected for the present study were 300 K inlet air, 0.4 overall equivalence ratio, and pressures of 1 and 10 bar. The numerical model used here involved the solution of time-averaged governing equations using an elliptic flow-field solver. The turbulence was modeled using algebraic stress modeling (ASM). The thermochemical model was based on the laminar flame let formulation. The conserved scalar/assumed pdf approach was used to model the turbulence chemistry interaction. The study was for two pressure cases at 1 and 10 bar. The turbulence–chemistry interaction is closed by assumption of a clipped Gaussian function form for the fluctuations in the mixture fraction. The kinetic calculations were done separately from the flowfield solver using an opposed laminar diffusion flame code of SANDIA. The temperature and species profiles were made available to the computations through look-up tables. The pollutants studied in this work were soot and NO for which three more additional transport equations are required, namely: averaged soot mass fraction, averaged soot particle number density, and finally averaged NO mass fraction. Soot oxidation was modeled using molecular oxygen only and a strong influence of pressure was predicted. Pressure was shown to have a major effect on soot formation.

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