A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Michael Kolb ◽  
Denise Ahrens ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Time Scale ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Dimensionless Number ◽  
Staged Combustion ◽  
Flow Temperature ◽  
Jet Flame ◽  
Lift Off

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multistage combustion to lower nitric oxide emissions and enhance turn-down ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large-scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off (LO) behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet LO depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K), and jet momentum ratio (6–210). The differences to existing LO studies are the high cross flow temperature and applying a premixed jet. The LO height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the LO height for similar staged combustion systems. A main outcome of this work is that the LO height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz-number. Furthermore, the ignition delay time scale τign also misses part of the LO height mechanism. The presented model uses turbulent time scales, the ignition delay, and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

2015 ◽  
Author(s):  
Michael Kolb ◽  
Denise Ahrens ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Time Scale ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Staged Combustion ◽  
Flow Temperature ◽  
Jet Flame ◽  
Stage Combustion ◽  
Lift Off

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multi-stage combustion to lower nitric oxide emissions and enhance turndown ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet lift-off depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K) and jet momentum ratio (6–210). The differences to existing lift-off studies are the high cross flow temperature and applying a premixed jet. The lift-off height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the lift-off height for similar staged combustion systems. A main outcome of this work is that the lift-off height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz number. Furthermore, the ignition delay time scale τign also misses part of the lift-off height mechanism. The presented model uses turbulent time scales, the ignition delay and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

Flame Hysteresis Effects in Methane Jet Flames in Air-Coflow

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
N. J. Moore ◽  
S. D. Terry ◽  
K. M. Lyons
Keyword(s):  
Turbulent Flows ◽  
Flame Stabilization ◽  
Hysteretic Behavior ◽  
Downstream Location ◽  
Jet Flame ◽  
Velocity Magnitude ◽  
Fuel Flow ◽  
Nozzle Exit Velocity ◽  
Lift Off ◽  
Flame Behavior

Presented are the results of experiments designed to investigate flame lift-off behavior in the hysteresis regime for low Reynolds number turbulent flows. The hysteresis regime refers to the situation where the jet flame has dual positions favorable to flame stabilization: attached and lifted. Typically, a jet flame is lifted off of a burner and stabilized at some downstream location at a pair of fuel and coflow velocities that is unique to a flame at that position. Since the direction from which that condition is arrived at is important, there is an inherent hysteretic behavior. To supplement previous research on hysteretic behavior in the presence of no coflow and low coflow velocities, the current research focuses on flames that are lifted and reattached at higher coflow velocities, where the flame behavior includes an unexpected downstream recession at low fuel velocities. Observations on the flame behavior related to nozzle exit velocity and coflow velocity are made using video imaging of flame sequences. The results show that a flame can stabilize at a location downstream despite a decrease in the local excess jet velocity and assist in determining the effect of coflow velocity magnitude on hysteretic behavior. These observations are of utility in designing maximum turndown burners in air coflow, especially for determining stability criteria in low fuel-flow applications.

Modeling and numerical study of H2/N2 jet flame in vitiated co-flow using Eulerian PDF transport approach

2018 ◽  
Vol 19 (5) ◽  
pp. 504
Author(s):  
Ahmed Amine Larbi ◽  
Abdelhamid Bounif ◽  
Mohamed Bouzit
Keyword(s):  
Parametric Study ◽  
Numerical Study ◽  
Delta Function ◽  
Flame Stabilization ◽  
Model Accuracy ◽  
Ansys Fluent ◽  
Jet Flame ◽  
Eulerian Approach ◽  
Lift Off ◽  
The Impact

The multi-environment Eulerian approach (MEPDF) is the eulerian method to solve the PDF transport equations; it is considered a product of the delta function. Its advantages are the prediction of extinction and ignition of the flame, also the kinetic control of the species as CO and NOX. Even though the MEPDF approach has been improved in recent years, most improvements have been achieved with parametric study in order to investigate the impact of the model accuracy. The main objective of this work is to improve further the model accuracy, the prediction of the lift off height by a parametric study of the mixing constant and Schmidt number and to understand its impact in flame stabilization. The numerical investigation of H2/N2 jet flame in vitiated co-flow is presented using MEPDF approach. The study was applied with K-epsilon modified model of turbulence. The chosen mixture model is the IEM (Interaction by Exchange with the Mean). The number of environment in the multi-environment Eulerian approach MEPDF is (2.0). The model was solved in this work by the commercial CFD code, ANSYS fluent and the chemical reaction mechanism injected is GRI mech 2.1. The results are validated with experimental data and discussed.

scholarly journals Staged combustion concept for gas turbines

2017 ◽  
Vol 1 ◽  
pp. CVLCX0 ◽  
Author(s):  
Dieter Winkler ◽  
Weiqun Geng ◽  
Geoffrey Engelbrecht ◽  
Peter Stuber ◽  
Klaus Knapp ◽  
...  
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Cross Flow ◽  
Staged Combustion ◽  
Cfd Simulations ◽  
Flow Configuration ◽  
Turbulent Flame Speed ◽  
Second Stage ◽  
Jet In Cross Flow

AbstractGas turbine power plants with high load flexibility are particularly suitable to compensate power fluctuations of wind and solar plants. Conventional gas turbines suffer from higher emissions at low load operation. With the objective of improving this situation a staged combustion system has been investigated. At low gas turbine load an upstream stage (first stage) provides stable combustion at low emissions while at higher loads the downstream stage (second stage) is started to supplement the power. Three injection geometries have been studied by means of computational fluid dynamics (CFD) simulations and atmospheric tests. The investigated geometries were a simple annular gap, a jet-in-cross-flow configuration and a lobe mixer. With CFD simulations the quality of mixing of second stage fresh gas with first stage exhaust gas was assessed. The lobe mixer showed the best mixing quality and hence was expected to also be the best variant in terms of combustion. However atmospheric combustion tests showed lower emissions for the jet-in-cross-flow configuration. Comparing flame photos in the visible and ultraviolet (UV) range suggest that the flame might be lifted off for the lobe mixer, leading to insufficient time for carbon monoxide (CO) burnout. CFD analysis of turbulent flame speed, turbulence and strain rates support the hypotheses of lifted off flame. Overall the staged concept was found to show very promising results not only with natural gas but also with natural gas enriched with propane or hydrogen. The investigations showed that apart from having an efficient and compact mixing of the two stages it is also very important to design the flow field such that the second flame can be anchored properly in order to achieve compact flames with sufficient time for CO burnout.

Experimental Investigation of the Combustion Behavior of Single-Nozzle Liquid-Flox®-Based Burners on an Atmospheric Test Rig

2020 ◽  
Author(s):  
Saeed Izadi ◽  
Jan Zanger ◽  
Oliver Kislat ◽  
Benedict Enderle ◽  
Felix Grimm ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Gas Turbines ◽  
Liquid Fuel ◽  
Gas Flow ◽  
Thermal Power ◽  
Cross Flow ◽  
Flame Length ◽  
Design Parameters ◽  
Gaseous Fuels ◽  
Lift Off

Abstract As an alternative to the commonly used swirl burners in micro gas turbines (MGT), the FLOX®-based combustion concept promises great potential for the nitric oxide emission reduction and increased fuel flexibility. Previous research on FLOX®-based MGT combustors mainly addressed gaseous fuels and there is less experience available on liquid fuel FLOX®-based MGT combustors. A FLOX®-based liquid fuel burner is developed to fit into a newly designed combustor for the Capstone C30 MGT. The studied FLOX®-based burners consist of an air nozzle with a coaxially arranged fuel pressure atomizer. The combustion chamber walls are made of quartz glass to enable optical accessibility for analyzing the structural properties of the flame. Furthermore, a diagonal hot cross-flow is arranged to emulate the annular hot gas flow of the other two burners in the MGT. The cross-flow is realized by utilizing a 20-nozzle FLOX®-based natural gas combustor. Measurements include visualization of the reaction zone and analysis of the exhaust gas emissions. By detecting the hydroxyl radical chemiluminescence (OH*-CL) emissions, the position of the heat release zone within the combustion chamber is attained. Correspondingly, the flame lift-off height and flame length are calculated. The investigated design parameters include air preheat temperature up to 733 K, equivalence ratio, burner geometry, and thermal power. The work presented in this paper aims to deepen the understanding of the design parameter interactions involved within the single-nozzle liquid-FLOX®-based burners.

Understanding the effect of inter-jet spacing on lift-off length and ignition delay

2021 ◽  
Vol 230 ◽  
pp. 111423
Author(s):  
Raul Payri ◽  
Jaime Gimeno ◽  
Marcos Carreres ◽  
Tomas Montiel
Keyword(s):  
Ignition Delay ◽  
Lift Off

Reduction of NOx Emission of Heavy Duty Gas Turbines by Improving Mixing Quality Using CFD Tools

2003 ◽  
Author(s):  
Weiqun Geng ◽  
Douglas Pennell ◽  
Stefano Bernero ◽  
Peter Flohr
Keyword(s):  
Gas Turbines ◽  
Mass Fraction ◽  
Cross Flow ◽  
Nox Emission ◽  
Injection System ◽  
Water Tunnel ◽  
Injection Hole ◽  
Fuel Mass ◽  
Mixing Quality ◽  
Fuel Mass Fraction

Jets in cross flow are one of the fundamental issues for mixing studies. As a first step in this paper, a generic geometry of a jet in cross flow was simulated to validate the CFD (Computational Fluid Dynamics) tool. Instead of resolving the whole injection system, the effective cross-sectional area of the injection hole was modeled as an inlet surface directly. This significantly improved the agreement between the CFD and experimental results. In a second step, the calculated mixing in an ALSTOM EV burner is shown for varying injection hole patterns and momentum flux ratios of the jet. Evaluation of the mixing quality was facilitated by defining unmixedness as a global non-dimensional parameter. A comparison of ten cases was made at the burner exit and on the flame front. Measures increasing jet penetration improved the mixing. In the water tunnel the fuel mass fraction within the burner and in the combustor was measured across five axial planes using LIF (Laser Induced Fluorescence). The promising hole patterns chosen from the CFD computations also showed a better mixing in the water tunnel than the other. Distribution of fuel mass fraction and unmixedness were compared between the CFD and LIF results. A good agreement was achieved. In a final step the best configuration in terms of mixing was checked with combustion. In an atmospheric test rig measured NOx emissions confirmed the CFD prediction as well. The most promising case has about 40% less NOx emission than the base case.

NOx Reduction Strategy by Staged Combustion with Plasma-Assisted Flame Stabilization

2012 ◽  
Vol 26 (7) ◽  
pp. 4284-4290 ◽  
Author(s):  
Dae Hoon Lee ◽  
Kwan-Tae Kim ◽  
Hee Seok Kang ◽  
Young-Hoon Song ◽  
Jae Eon Park
Keyword(s):  
Nox Reduction ◽  
Flame Stabilization ◽  
Staged Combustion ◽  
Reduction Strategy

scholarly journals The Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen–Nitrogen Mixtures in Vitiated Air of High Temperature

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Christoph A. Schmalhofer ◽  
Peter Griebel ◽  
Manfred Aigner
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
High Speed ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Promoting Effect ◽  
Experimental Conditions ◽  
Lean Premixed Combustion ◽  
Image Velocimetry ◽  
Fuel Mixtures

The use of highly reactive hydrogen-rich fuels in lean premixed combustion systems strongly affects the operability of stationary gas turbines (GT) resulting in higher autoignition and flashback risks. The present study investigates the autoignition behavior and ignition kernel evolution of hydrogen–nitrogen fuel mixtures in an inline co-flow injector configuration at relevant reheat combustor operating conditions. High-speed luminosity and particle image velocimetry (PIV) measurements in an optically accessible reheat combustor are employed. Autoignition and flame stabilization limits strongly depend on temperatures of vitiated air and carrier preheating. Higher hydrogen content significantly promotes the formation and development of different types of autoignition kernels: More autoignition kernels evolve with higher hydrogen content showing the promoting effect of equivalence ratio on local ignition events. Autoignition kernels develop downstream a certain distance from the injector, indicating the influence of ignition delay on kernel development. The development of autoignition kernels is linked to the shear layer development derived from global experimental conditions.

scholarly journals Nitrogen Oxide Reduction by Staged Combustion of Biomass Gas in Gas Turbines — A Modeling Study of the Effect of Mixing

1999 ◽  
Author(s):  
Edgardo G. Coda Zabetta ◽  
Pia T. Kilpinen ◽  
Mikko M. Hupa ◽  
Jukka K. Leppälahti ◽  
C. Krister O. Ståhl ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Nox Reduction ◽  
Plug Flow ◽  
Chemical Kinetic ◽  
Process Variables ◽  
Staged Combustion ◽  
Fuel Gas ◽  
Effective Option ◽  
Fuel Mixing ◽  
Lower Temperature

Detailed chemical kinetic modeling has been used to study the reduction of nitrogen oxides at gas turbine (GT) combustor conditions. A gas from gasification of wood with air has been used as the fuel. An air-staged combustion technique has been adapted. In our previous study a simple plug flow model was used to study the effects of pressure and temperature among others process variables. The air-fuel mixing was assumed perfect and instantaneous. Results showed the NOx reduction mainly affected by both pressure and temperature. The aim of the present work is to establish the effect of air-fuel mixing delay on NOx predictions and to extrapolate indications options for GT. To model the mixing delay, a varying number of air sub-streams are mixed with the fuel gas during different time periods. Alternatively, a combination of a perfectly mixed zone followed by a plug flow zone is illustrated. Results by any air-fuel mixing model show similar affect of process variables on NOx reduction. When a mixing delay is assumed instead of the instantaneous mixing the NOx reduction is enhanced, and only with delayed mixing NOx are affected by CH4. Lower temperature and higher pressure in the GT-combustor can enhance the NOx reduction. Also air staging is an effective option: a 3 stages combustor designed for low mixing speed appear competitive compared to more complicate combustors. The fewer hydrocarbons in the gasification gas the high NOx reduction.

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