scholarly journals On the Flame Shape in a Premixed Swirl Stabilised Burner and its Dependence on the Laminar Flame Speed

2021 ◽  
Author(s):  
Nikolaos Papafilippou ◽  
Muhammad Aqib Chishty ◽  
Richard Bart Gebart
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Fossil Fuels ◽  
Numerical Solutions ◽  
Laminar Flame ◽  
Methane Combustion ◽  
Axial Direction ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Flame Shape

AbstractGas turbines for power generation are optimised to run with fossil fuels but as a response to tighter pollutant regulations and to enable the use of renewable fuels there is a great interest in improving fuel flexibility. One interesting renewable fuel is syngas from biomass gasification but its properties vary depending on the feedstock and gasification principle, and are significantly different from conventional fuels. This paper aims to give an overview of the differences in combustion behaviour by comparing numerical solutions with methane and several different synthesis gas compositions. The TECFLAM swirl burner geometry, which is designed to be representative of common gas turbine burners, was selected for comparison. The advantage with this geometry is that detailed experimental measurements with methane are publicly available. A two-stage approach was employed with development and validation of an advanced CFD model against experimental data for methane combustion followed by simulations with four syngas mixtures. The validated model was used to compare the flame shape and other characteristics of the flow between methane, 40% hydrogen enriched methane and four typical syngas compositions. It was found that the syngas cases experience lower swirl intensity due to high axial velocities that weakens the inner recirculation zone. Moreover, the higher laminar flame speed of the syngas cases has a strong effect on the flame front shape by bending it away from the axial direction, by making it shorter and by increasing the curvature of the flame front. A hypothesis that the flame shape and position is primarily governed by the laminar flame speed is supported by the almost identical flame shapes for bark powder syngas and 40% hydrogen enriched methane. These gas mixtures have almost identical laminar flame speeds for the relevant equivalence ratios but the heating value of the syngas is more than a factor of 3 smaller than that of the hydrogen enriched methane. The syngas compositions used are representative of practical gasification processes and biomass feedstocks. The demonstrated strong correlation between laminar flame speed and flame shape could be used as a rule of thumb to quickly judge whether the flame might come in contact with the structure or in other ways be detrimental to the function of the combustion system.

Laminar Flame Speed Measurements and Modeling of Pure Alkanes and Alkane Blends at Elevated Pressures

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
William Lowry ◽  
Jaap de Vries ◽  
Michael Krejci ◽  
Eric Petersen ◽  
Zeynep Serinyel ◽  
...  
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Turbines ◽  
Laminar Flame ◽  
Flame Speed ◽  
Published Data ◽  
Laminar Flame Speed ◽  
Binary Blends ◽  
Elevated Pressures ◽  
True Value

Alkanes such as methane, ethane, and propane make up a large portion of most natural gas fuels. Natural gas is the primary fuel used in industrial gas turbines for power generation. Because of this, a fundamental understanding of the physical characteristics such as the laminar flame speed is necessary. Most importantly, this information is needed at elevated pressures to have the most relevance to the gas turbine industry for engine design. This study includes experiments performed at elevated pressures, up to 10 atm initial pressure, and investigates the fuels in a pure form as well as in binary blends. Flame speed modeling was done using an improved version of the kinetics model that the authors have been developing over the past few years. Modeling was performed for a wide range of conditions, including elevated pressures. Experimental conditions include pure methane, pure ethane, 80/20 mixtures of methane/ethane, and 60/40 mixtures of methane/ethane at initial pressures of 1 atm, 5 atm, and 10 atm. Also included in this study are pure propane and 80/20 methane/propane mixtures at 1 atm and 5 atm. The laminar flame speed and Markstein length measurements were obtained from a high-pressure flame speed facility using a constant-volume vessel. The facility includes optical access, a high-speed camera, a schlieren optical setup, a mixing manifold, and an isolated control room. The experiments were performed at room temperature, and the resulting images were analyzed using linear regression. The experimental and modeling results are presented and compared with previously published data. The data herein agree well with the published data. In addition, a hybrid correlation was created to perform a rigorous uncertainty analysis. This correlation gives the total uncertainty of the experiment with respect to the true value rather than reporting the standard deviation of a repeated experiment. Included in the data set are high-pressure results at conditions where in many cases for the single-component fuels few data existed and for the binary blends no data existed prior to this study. Overall, the agreement between the model and data is excellent.

High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions

2019 ◽  
Author(s):  
Pradeep Parajuli ◽  
Tyler Paschal ◽  
Mattias A. Turner ◽  
Eric L. Petersen ◽  
Waruna D. Kulatilaka
Keyword(s):  
Natural Gas ◽  
Flame Front ◽  
Gas Turbines ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Initial Pressure ◽  
Flame Speed ◽  
Operating Conditions ◽  
Important Species

Abstract Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.

An Investigation of Laminar Flame Speed of CH4-O2-CO2 Mixtures

2019 ◽  
Author(s):  
Mattias A. Turner ◽  
Tyler Paschal ◽  
Waruna D. Kulatilaka ◽  
Eric L. Petersen
Keyword(s):  
Supercritical Co2 ◽  
Carbon Capture ◽  
High Speed ◽  
Laminar Flame ◽  
Full Range ◽  
Methane Combustion ◽  
Fuel Combustion ◽  
Flame Speed ◽  
Working Fluid ◽  
Laminar Flame Speed

Abstract The push for lower carbon emissions in power generation has driven interest in methods of carbon capture and sequestration. One such promising method involves the supercritical CO2 (sCO2) power cycle, a system which is powered by oxy-fuel combustion where supercritical carbon dioxide is used as the working fluid. The high CO2 concentration in the combustion products allows for relatively simple extraction of CO2 from the system. Although this is an active field of research, the design of such a combustor requires continued study of oxy-fuel combustion in high levels of CO2 diluent. With that objective in mind, laminar flame experiments were conducted for CH4-O2-CO2 mixtures at one atmosphere and room temperature, where the relative concentrations of O2 and CO2 in the oxidizer mixture were 34.0% and 66.0% by mole, respectively. These concentrations were chosen to ensure the flame would propagate quickly enough to overcome the effects of buoyancy, which were observed to become significant below laminar flame speeds of roughly 15 cm/s. A high-speed chemiluminescence imaging diagnostic was employed in place of the traditional schlieren technique. Laminar flame speed was measured from OH* emission at 306 nm for a full range of equivalence ratios, varying from 15.2 cm/s at 0.7 to 24.8 cm/s at stoichiometric. Additionally, images of OH* chemiluminescence of turbulent CH4-O2-CO2 flames and of quiescent, 5-atm CH4-O2-CO2 flames at stoichiometric concentration are also presented. These experiments provide useful data for validation of chemical kinetics models for oxy-methane combustion in a CO2 diluent, which can be applied to the modeling of oxy-methane combustion for supercritical CO2 power cycles.

Multi-Dimensional CFD Simulations of Knocking Combustion in a CFR Engine

2017 ◽  
Author(s):  
Pinaki Pal ◽  
Yunchao Wu ◽  
Tianfeng Lu ◽  
Sibendu Som ◽  
Yee Chee See ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flame Front ◽  
Octane Number ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Equation Model ◽  
Flame Speed ◽  
Lookup Table ◽  
Laminar Flame Speed ◽  
Skeletal Mechanism

Knock is a major impediment to achieving higher efficiency in Spark-Ignition (SI) engines. The recent trends of boosting, downsizing and downspeeding have exacerbated this issue by driving engines toward higher power density and higher load duty cycles. Apart from the engine operating conditions, fuel anti-knock quality is a major determinant of the knocking tendency in engines, as quantified by its octane number (ON). The ON of a fuel is based on an octane scale which is defined according to the standard octane rating methods for Research Octane Number (RON) and Motor Octane Number (MON). These tests are performed in a single cylinder Cooperative Fuel Research (CFR) engine. In the present work, a numerical approach was developed based on multidimensional computational fluid dynamics (CFD) to predict knocking combustion in a CFR engine. The G-equation model was employed to track the propagation of the turbulent flame front and a multi-zone model based on temperature and equivalence ratio was used to capture auto-ignition in the endgas ahead of the flame front. Furthermore, a novel methodology was developed wherein a lookup table generated from a chemical kinetic mechanism could be employed to provide laminar flame speed as an input to the G-equation model, instead of using empirical correlations. To account for fuel chemistry effects accurately and lower the computational cost, a compact 121-species primary reference fuel (PRF) skeletal mechanism was developed from a more detailed gasoline surrogate mechanism using the directed relation graph assisted sensitivity analysis (DRGASA) reduction technique. Extensive validation of the skeletal mechanism was performed against experimental data available in the literature for both homogeneous ignition delay and laminar flame speed. The skeletal mechanism was used to generate the lookup tables for laminar flame speed as a function of pressure, temperature and equivalence ratio. The engine CFD model incorporating the skeletal mechanism was employed to perform numerical simulations under RON and MON conditions for different PRFs. Parametric tests were conducted at different compression ratios and the predicted values of critical compression ratio (at knock onset), delineating the boundary between “no knock” and “knock”, were found to be in good agreement with the available experimental data. The virtual CFR engine model was, therefore, demonstrated to be capable of adequately capturing the sensitivity of knock propensity to fuel chemistry.

Numerical Study on the Effect of Real Syngas Compositions on Ignition Delay Times and Laminar Flame Speeds at Gas Turbine Conditions

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Olivier Mathieu ◽  
Eric L. Petersen ◽  
Alexander Heufer ◽  
Nicola Donohoe ◽  
Wayne Metcalfe ◽  
...  
Keyword(s):  
Ignition Delay ◽  
Delay Time ◽  
Gas Turbines ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Laminar Flame Speed ◽  
Ignition Delay Times ◽  
Delay Times

Depending on the feedstock and the production method, the composition of syngas can include (in addition to H2 and CO) small hydrocarbons, diluents (CO2, water, and N2), and impurities (H2S, NH3, NOx, etc.). Despite this fact, most of the studies on syngas combustion do not include hydrocarbons or impurities and in some cases not even diluents in the fuel mixture composition. Hence, studies with realistic syngas composition are necessary to help in designing gas turbines. The aim of this work was to investigate numerically the effect of the variation in the syngas composition on some fundamental combustion properties of premixed systems such as laminar flame speed and ignition delay time at realistic engine operating conditions. Several pressures, temperatures, and equivalence ratios were investigated for the ignition delay times, namely 1, 10, and 35 atm, 900–1400 K, and ϕ = 0.5 and 1.0. For laminar flame speed, temperatures of 300 and 500 K were studied at pressures of 1 atm and 15 atm. Results showed that the addition of hydrocarbons generally reduces the reactivity of the mixture (longer ignition delay time, slower flame speed) due to chemical kinetic effects. The amplitude of this effect is, however, dependent on the nature and concentration of the hydrocarbon as well as the initial condition (pressure, temperature, and equivalence ratio).

The Effect of Impurities on Ignition Delay Times and Laminar Flame Speeds of Syngas Mixtures at Gas Turbine Conditions

2014 ◽  
Author(s):  
Olivier Mathieu ◽  
Joshua W. Hargis ◽  
Eric L. Petersen ◽  
John Bugler ◽  
Henry J. Curran ◽  
...  
Keyword(s):  
Ignition Delay ◽  
Delay Time ◽  
Gas Turbines ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Laminar Flame Speed ◽  
Ignition Delay Times ◽  
Combustion Properties

In addition to mostly H2 and CO, syngas also contains reasonable amounts of light hydrocarbons, CO2, H2O, N2, and Ar. Impurities such as NH3, HCN, COS, H2S, and NOx (NO, NO2, N2O) are also commonly found in syngas. The presence of these impurities, even in very low concentrations, can induce some large changes in combustion properties. Although they introduce potential design and operational issues for gas turbines, these changes in combustion properties due to the presence of impurities are still not well characterized. The aim of this work was therefore to investigate numerically the effect of the presence of impurities in realistic syngas compositions on some fundamental combustion properties of premixed systems such as laminar flame speed and ignition delay time, at realistic engine operating conditions. To perform this study, a state-of-the-art C0–C3 detailed kinetics mechanism was used. This mechanism was combined with recent, optimized sub-mechanisms for impurities which can impact the combustion properties of the syngas such as nitrogenous species (i.e., N2O, NO2, NH3, and HCN) and sulfur-based species such as H2S, SO2 and COS. Several temperatures, pressures, and equivalence ratios were investigated. The results of this study showed that the addition of some impurities modifies notably the reactivity of the mixture. The ignition delay time is decreased by the addition of NO2 and H2S at the temperatures and pressures for which the HO2 radical dominates the H2 combustion. However, while NO2 has no effect when OH is dominating, H2S increases the ignition delay time in such conditions for pressures above 1 atm. The amplitude of these effects is however dependent on the impurity concentration. Laminar flame speeds are not sensitive to NO2 addition but they are to NH3 and HCN, inducing a small reduction of the laminar flame speed at fuel rich conditions. H2S exhibits some inhibiting effects on the laminar flame speed but only for high concentrations. The inhibiting effects of NH3, HCN, and H2S are due to the OH radical consumption by these impurities, leading to the formation of radicals that are less reactive.

Laminar Flame Speed Measurements and Modeling of Pure Alkanes and Alkane Blends at Elevated Pressures

2010 ◽  
Author(s):  
William Lowry ◽  
Jaap de Vries ◽  
Michael Krejci ◽  
Eric Petersen ◽  
Zeynep Serinyel ◽  
...  
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Turbines ◽  
Laminar Flame ◽  
Flame Speed ◽  
Published Data ◽  
Laminar Flame Speed ◽  
Binary Blends ◽  
Elevated Pressures ◽  
True Value

Alkanes such as methane, ethane, and propane make up a large portion of most natural gas fuels. Natural gas is the primary fuel used in industrial gas turbines for power generation. Because of this, a fundamental understanding of the physical characteristics such as the laminar flame speed is necessary. Most importantly, this information is needed at elevated pressures to have the most relevance to the gas turbine industry for engine design. This study includes experiments performed at elevated pressures, up to 10-atm initial pressure, and investigates the fuels in a pure form as well as in binary blends. Flame speed modeling was done using an improved version of the kinetics model that the authors have been developing over the past few years. Modeling was performed for a wide range of conditions, including elevated pressures. Experimental conditions include pure methane, pure ethane, 80/20 mixtures of methane/ethane, and 60/40 mixtures of methane/ethane at initial pressures of 1, 5, and 10 atm. Also included in this study are pure propane and 80/20 methane/propane mixtures at 1 and 5 atm. The laminar flame speed and Markstein Length measurements were obtained from a high-pressure flame speed facility using a constant-volume vessel. The facility includes optical access, a high-speed camera, a schlieren optical setup, a mixing manifold, and an isolated control room. The experiments were performed at room temperature, and the resulting images were analyzed using linear regression. The experimental and modeling results are presented and compared to previously published data. The data herein agree well with the published data. In addition, a hybrid correlation was created to perform a rigorous uncertainty analysis. This correlation gives the total uncertainty of the experiment with respect to the true value rather than reporting the standard deviation of a repeated experiment. Included in the data set are high-pressure results at conditions where in many cases for the single-component fuels few data existed and for the binary blends no data existed prior to this study. Overall, the agreement between the model and data is excellent.

A Numerical Study on the Reactivity of Biogas/Reformed-Gas/Air and Methane/Reformed-Gas/Air Mixtures at Gas Turbine Relevant Conditions

2016 ◽  
Author(s):  
Pablo Diaz Gomez Maqueo ◽  
Philippe Versailles ◽  
Gilles Bourque ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Gas Turbine ◽  
Laminar Flame ◽  
Numerical Study ◽  
Flame Temperature ◽  
Flame Speed ◽  
Flame Stability ◽  
Laminar Flame Speed ◽  
Fuel Reforming ◽  
Numerical Work ◽  
Chemical Effects

This study investigates the increase in methane and biogas flame reactivity enabled by the addition of syngas produced through fuel reforming. To isolate thermodynamic and chemical effects on the reactivity of the mixture, the burner simulations are performed with a constant adiabatic flame temperature of 1800 K. Compositions and temperatures are calculated with the chemical equilibrium solver of CANTERA® and the reactivity of the mixture is quantified using the adiabatic, freely-propagating premixed flame, and perfectly-stirred reactors of the CHEMKIN-Pro® software package. The results show that the produced syngas has a content of up to 30 % H2 with a temperature up to 950 K. When added to the fuel, it increases the laminar flame speed while maintaining a burning temperature of 1800 K. Even when cooled to 300 K, the laminar flame speed increases up to 30 % from the baseline of pure biogas. Hence, a system can be developed that controls and improves biogas flame stability under low reactivity conditions by varying the fraction of added syngas to the mixture. This motivates future experimental work on reforming technologies coupled with gas turbine exhausts to validate this numerical work.

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