ROLE OF INLET BOUNDARY CONDITIONS ON FUEL-AIR MIXING AT SUPERCRITICAL CONDITIONS

2021 ◽  
pp. 1-22
Author(s):  
Zachary Harris ◽  
Joshua Bittle ◽  
Ajay Agrawal
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Gas Turbines ◽  
Alternative Fuels ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Supercritical Conditions ◽  
Complex Interactions ◽  
Significant Research ◽  
Air Mixing

Abstract Advanced engine design and alternative fuels present the possibility of fuel injection at purely supercritical conditions in diesel engines and gas turbines. The complex interactions that govern this phenomenon still need significant research, particularly the boundary conditions for fuel injection are critical for accurate simulation. However, the flow inside the injector itself is often omitted to reduce the computational efforts, and thus, velocity, mass flux, or total pressure is specified at the injector exit (or domain inlet), often with simplified velocity profiles and turbulence levels. This simplified inlet boundary treatment has minimal effects on results for conventional fuel injection conditions, however, the validity of this approach at supercritical conditions has not been assessed. Comprehensive real-gas and binary fluid mixing models have been implemented for computational fluid dynamic (CFD) analysis of fuel-air mixing at supercritical conditions. The model is verified using prior CFD results from the literature. The model is used to investigate the effects of the shape of axial velocity and mass fraction profiles at the inlet boundary with the goal to improve the comparison of predictions to experimental data. Results show that the boundary conditions have a significant effect on the predictions, and none of the cases match precisely with experimental data. The study reveals that the physical location of the inlet boundary might be difficult to infer correctly from the experiments and highlights the need for high-quality, repeatable measurements at supercritical conditions to support the development of relevant high-fidelity models for fuel-air mixing.

Role of Inlet Boundary Conditions on Fuel-Air Mixing at Supercritical Conditions

2020 ◽  
Author(s):  
Zachary Harris ◽  
Joshua Bittle ◽  
Ajay Agrawal
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Gas Turbines ◽  
Alternative Fuels ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Supercritical Conditions ◽  
Complex Interactions ◽  
Significant Research ◽  
Air Mixing

Abstract Advanced engine design and alternative fuels present the possibility of fuel injection at purely supercritical conditions in diesel engines and gas turbines. The complex interactions that govern this phenomenon still need significant research for reliable modeling efforts. Boundary conditions for fuel injection are critical to accurate simulation. However, the flow inside the injector itself is often omitted to reduce the computational efforts, and thus, velocity, mass flux, or total pressure is specified at the injector exit (or domain inlet), often with an assumed top hat profile and assumed turbulence levels. Past studies have shown that such simplified inlet boundary treatment has minimal effects on the results for fuel injection in the compressed liquid phase. However, the validity of this approach at supercritical fuel injection conditions has not been assessed so far. In this study, comprehensive real-gas and binary fluid mixing models have been implemented for computational fluid dynamic (CFD) analysis of fuel-air mixing at supercritical conditions. The model is verified using prior CFD results from the literature. Next, the model is used to investigate the effects of the shape of axial velocity and mass fraction profiles at the inlet boundary with the goal to improve the comparison of predictions to experimental data. Results show that the boundary conditions have a significant effect on the predictions, and none of the cases match precisely with experimental data. The study reveals that the physical location of the inlet boundary might be difficult to infer correctly from the experiments and highlights the need for high-quality, repeatable measurements at supercritical conditions to support the development of relevant high-fidelity models for fuel-air mixing.

Center Body Burner for Sequential Combustion: Superior Performance at Lower Emissions

2021 ◽  
Author(s):  
A. Ciani ◽  
J. P. Wood ◽  
M. Maurer ◽  
B. Bunkute ◽  
D. Pennell ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Mixture Fraction ◽  
Nox Reduction ◽  
Water Channel ◽  
Superior Performance ◽  
Fuel Flexibility ◽  
Air Mixing ◽  
Center Body

Abstract Modern gas turbines call for an ultra-high firing temperature and fuel flexibility while keeping emissions at very low levels. Sequential combustion has demonstrated its advantages toward such ambitious targets. A sequential combustion system, as deployed in the GT26 and GT36 engines, consists of two burners in series, the first one optimized to provide the optimum boundary condition for the second one, the sequential burner. This is the key component for the achievement of the required combustor performance dictated by F and H class engines, including versatile and robust operation with hydrogen-based fuels. This paper describes the key development considerations used to establish a new sequential burner surpassing state-of-the-art hardware in terms of emission reduction, fuel flexibility and load flexibility. A novel multi-point injector geometry was deployed based on combustion and fluid dynamic considerations to maximize fuel / air mixing quality at minimum pressure loss. Water channel experiments complemented by CFD describe the evolution of the fuel / air mixture fraction through the mixing section and combustion chamber to enable operation with major NOx reduction. Furthermore, Laser Doppler Anemometry and Laser Induced Fluorescence were used to best characterize the interaction between hot-air and fuel and the fuel / air mixing in the most critical regions of the system. To complete the overview of the key development steps, mechanical integrity and manufacturing considerations based on additive manufacturing are also presented. The outcome of 1D, CFD and fluid dynamic experimental findings were then validated through full-scale, full-pressure combustion tests. These demonstrate the novel Center Body Burner is enabling operation at lower emissions, both at part load and full load conditions. Furthermore, the validation of the burner was also extended to hydrogen-based fuels with a variety of hydrogen / natural gas blends.

Experimental Validation of Methods Providing Boundary Conditions to Simulate the Evaporation Process of Water Injected Into High Speed Air Flow

2013 ◽  
Author(s):  
P. S. Nagabhushan ◽  
A. Rossetti ◽  
B. Barabas ◽  
J. P. Schnitzler ◽  
A. Kefalas ◽  
...  
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Gas Turbines ◽  
High Speed ◽  
Air Flow ◽  
Computational Cost ◽  
Spray Angle ◽  
Diameter Distribution ◽  
Particle Injection ◽  
Lagrange Approach

Water injection into a high speed air flow has been recently investigated by many scientists and is still an important field of research in gas turbine technology. To study the behavior of droplets in gas turbines, expensive experimental tests and their validation with analytical and Computational Fluid Dynamics (CFD) models are necessary. The Euler-Lagrange approach can be used to tackle these problems due to their capability in tracking particles along the domain, relative ease in formulating and applying them to the current industrial problems in terms of acceptable computational cost. However, providing spray boundary conditions using Euler-Lagrange approach is quite challenging because the spray pattern depends upon various parameters like spray angle, velocity, diameter distribution etc. In this paper, to obtain these parameters, two different approaches are described. The first approach depends on an analytical model for velocity and spray angle injection conditions and the second approach depends on an Euler free surface simulation. For diameter distribution, Rosin Rammler distribution function and experimental data are used. When combined together these lead to four particle injection conditions. The results achieved from all the four cases are compared with the experimental data of water droplet evaporation in a high speed air flow obtained from a hot air test rig operating at conditions of real gas turbines.

Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner

2019 ◽  
Author(s):  
Heena Panchasara ◽  
Pankaj S. Kolhe ◽  
Ajay K. Agrawal
Keyword(s):  
Gas Turbine ◽  
Axial Velocity ◽  
Alternative Fuels ◽  
Dynamic Models ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Distribution Functions ◽  
Turbulent Dispersion ◽  
Radial Profiles

Abstract Fuel injection plays an important role in liquid fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel-air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio (ALR) by mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter are presented to show the effect of fuel preheating. Joint Probability Density Functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.

An Open Water Numerical Model for a Marine Propeller: A Comparison With Experimental Data

2002 ◽  
Author(s):  
Julia´n Marti´nez-Calle ◽  
Laureano Balbona-Calvo ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Eduardo Blanco-Marigorta
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Boundary Conditions ◽  
Test Performance ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Open Water ◽  
Water Model ◽  
Wake Field ◽  
Fishing Boat

The open water model tests technique is well known and commonly used to predict propellers performance. In this paper, a quite different approach is intended and the main propeller variables are numerically modelled using a finite volume commercial code. Particularly, a fishing-boat propeller is numerically treated using a three-dimensional unstructured mesh. Mesh dependency and different turbulent models are considered together with an sliding technique to account for the rotation. Typical turbomachinery boundary conditions for a volume containing the propeller are imposed (inlet velocity and outlet static pressure). In order to get the open water test performance coefficients for the considered propeller (KT, KQ, η), different advance coefficient (J) are imposed as boundary conditions for the numerical model. The results of such simulations are compared with experimental data available for the open water tests of the propeller. Once the model is validated with the experimental data available, a wake field simulation would be possible and would lead to the definition of the fluid-dynamic variables (pressure, iso-velocity maps, etc.) which are needed during any design process. Also some comparisons with real scale thrust measurements are intended.

Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Heena Panchasara ◽  
Pankaj S. Kolhe ◽  
Ajay K. Agrawal
Keyword(s):  
Gas Turbine ◽  
Axial Velocity ◽  
Alternative Fuels ◽  
Dynamic Models ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Distribution Functions ◽  
Turbulent Dispersion ◽  
Radial Profiles

Abstract Fuel injection plays an important role in liquid-fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel–air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast (AB) atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio by a mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter (SMD) are presented to show the effect of fuel preheating. Joint probability density functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.

scholarly journals Modelling of transcritical and supercritical nitrogen jets

2017 ◽  
Vol 169 (2) ◽  
pp. 125-132
Author(s):  
Eduardo ANTUNES ◽  
Andre SILVA ◽  
Jorge BARATA
Keyword(s):  
Gas Turbines ◽  
Internal Combustion Engines ◽  
Fuel Injection ◽  
Stokes Equations ◽  
Variable Density ◽  
Navier Stokes ◽  
Rocket Engines ◽  
Supercritical Conditions ◽  
Potential Core

The present paper addresses the modelling of fuel injection at conditions of high pressure and temperature which occur in a variety of internal combustion engines such as liquid fuel rocket engines, gas turbines, and modern diesel engines. For this investigation a cryogenic nitrogen jet ranging from transcritical to supercritical conditions injected into a chamber at supercritical conditions was modelled. Previously a variable density approach, originally conceived for gaseous turbulent isothermal jets, imploying the Favre averaged Navier-Stokes equations together with a “k-ε” turbulence model, and using Amagats law for the determination of density was applied. This approach allows a good agreement with experiments mainly at supercritical injection conditions. However, some departure from experimental data was found at transcritical injection conditions. The present approach adds real fluid thermodynamics to the previous approach, and the effects of heat transfer. The results still show some disagreement at supercritical conditions mainly in the determination of the potential core length but significantly improve the prediction of the jet spreading angle at transcritical injection conditions.

scholarly journals A Semi-Analytical Approach to Emissions Prediction in Gas Turbine Combustors

1998 ◽  
Author(s):  
Bruno Facchini ◽  
Giovanni Ferrara ◽  
Paolo Mazzilli
Keyword(s):  
Experimental Data ◽  
Gas Turbines ◽  
Critical Analysis ◽  
Fluid Dynamic ◽  
Computation Time ◽  
Pollutant Emissions ◽  
Combustion Model ◽  
Reduction Techniques ◽  
Pollutant Reduction ◽  
Good Agreement

An application of a simplified combustion model to pollutant emissions prediction in gas turbines is presented here. A critical analysis of the Rizk and Mongia semi-analytical model is conducted, and some corrections are accomplished to obtain a better agreement with experimental data. Special attention is devoted to the temperature equation, which is carefully modified, and to the schematization of several kinds of combustors. The simulation of some conventional pollutant reduction techniques, such as inert injection or exhaust gases re-circulation, is conducted with this corrected model. The results show a good agreement with experimental data both in conventional, and in innovative combustors, like Lean-Premixed or Rich-Lean concepts. The model needs a very short computation time and is likely to allow a simultaneous solution of chemical and fluid-dynamic aspect of the combustor.

Micro Mixing Fuel Injectors for Low Emissions Hydrogen Combustion

2008 ◽  
Author(s):  
Steven R. Hernandez ◽  
Qing Wang ◽  
Vincent McDonell ◽  
Adel Mansour ◽  
Erlendur Steinthorsson ◽  
...  
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Turbine Engines ◽  
Nox Emissions ◽  
Gas Turbine Engines ◽  
Fuel Injectors ◽  
Air Mixing ◽  
Potential Benefits ◽  
Computational Fluid Dynamics Cfd

The consideration of hydrogen as a fuel for next generation low emissions gas turbines raises a number of challenges and potential benefits relative to the combustion system. The present work examines the use of a micro-mixing injection strategy for hydrogen as a means to achieve rapid mixing and inherent flexibility for accommodating various staging, dilution, and dual fuel requirements for future gas turbine engines. The work presented includes numerical and experimental results associated with the fuel-air mixing process in a representative injector configuration. Measured NOx emissions and fuel/air ratios at the exit of the mixer are shown along with visualization of the reactions generated. Detailed computational fluid dynamics (CFD) is used in parallel to elucidate the behavior of the flow inside and downstream of the injectors. Results are also presented for natural gas to provide a point of reference. The results illustrate a number of interesting features and characteristics of the hydrogen/air mixtures which are in dramatic contrast to the behavior of natural gas/air mixtures. Comparison of the measured and modeled mixing behavior illustrates a number of challenges associated with the selection of a robust modeling approach for hydrogen/air combustion. The results demonstrate that the use of micro-mixing fuel injection to achieve ultra low NOx emissions is very promising.

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