Generating Laminar Flame Speed Libraries for Autoignition Conditions

2020 ◽  
Author(s):  
Karthik V. Puduppakkam ◽  
Abhijit U. Modak ◽  
Cheng Wang ◽  
Devin Hodgson ◽  
Chitralkumar V. Naik ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Laminar Flame ◽  
Combustion Engine ◽  
Flame Speed ◽  
Cfd Modeling ◽  
Laminar Flame Speed ◽  
Wide Range ◽  
Fuel Effects ◽  
Propagation Properties ◽  
Operating Points

Abstract With advanced gas turbine combustor and internal combustion engine designs, autoignition can happen alongside flame propagation. Laminar flame speeds are required to model flame propagation. Determining laminar flame speeds using simulation assumes flames are freely propagating, an assumption that is not valid when autoignition does occur. From a CFD modeling viewpoint however, it is useful to have extrapolated laminar flame-speed values over a wide range of conditions, to allow CFD to operate smoothly and avoid discontinuities while calculating flame-propagation properties. In this work we focus on developing an approach for generating laminar flame-speed libraries under both nonigniting and autoigniting conditions. Following a test of whether autoignition occurs, laminar flame speeds are either modeled or extrapolated. The details of the approach implemented and its validation are explained. We assess the accuracy of the extrapolation employed by calculating relevant coefficients based on flame speeds from nearby operating points. Recommendations are made for the time scales to be used in determining autoignition occurrence. Fuel effects are also explored in this context.

Optical and Numerical Investigations of Flame Propagation in a Heavy Duty Spark Ignited Natural Gas Engine

2021 ◽  
Author(s):  
Jinlong Liu ◽  
Christopher Ulishney ◽  
Cosmin E. Dumitrescu
Keyword(s):  
Natural Gas ◽  
Flame Propagation ◽  
Turbulence Intensity ◽  
Laminar Flame ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Heavy Duty ◽  
Piston Chamber

Abstract Increasing the natural gas (NG) use in heavy-duty engines is beneficial for reducing greenhouse-gas emissions from power generation and transportation. However, converting compression ignition (CI) engines to NG spark ignition operation can increase methane emissions without expensive aftertreatment, thereby defeating the purpose of utilizing a low carbon fuel. The widely accepted explanation for the low combustion efficiency in such retrofitted engines is the lower laminar flame speed of natural gas. In addition, diesel engine’s larger bowl size compared to the traditional gasoline engines increases the flame travel length inside the chamber and extends the combustion duration. However, optical measurements performed in this study suggested that a fast-propagating flame was developed inside the cylinder even at extremely lean operation. This was supported by a three-dimensional numerical simulation, which indicated that the squish region of the bowl-in-piston chamber generated a high turbulence intensity inside the bowl. However, the flame propagation experienced a sudden 2.25x reduction in speed when transiting from the bowl to the squish region. Such a phenomenon was caused by the large decrease in the turbulence intensity inside the squish region during the combustion process. Moreover, the squish volume trapped an important fuel fraction, and it is this fraction that experienced a slow and inefficient burning process during the expansion stroke. This resulted in increased methane emissions and reduced combustion efficiency. Overall, it was the specifics of the combustion process inside a bowl-in-piston chamber not the methane’s slow laminar flame speed that contributed to the low methane combustion efficiency for the retrofitted engine. The results suggest that optimizing the chamber shape is paramount to boost engine efficiency and decrease its emissions.

Laminar Flame Speed and Ignition Delay Time Data for the Kinetic Modeling of Hydrogen and Syngas Fuel Blends

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Michael C. Krejci ◽  
Olivier Mathieu ◽  
Andrew J. Vissotski ◽  
Sankaranarayanan Ravi ◽  
Travis G. Sikes ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Chemical Kinetics ◽  
Ignition Delay ◽  
Laminar Flame ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Elevated Pressures ◽  
Ignition Delay Times ◽  
Wide Range ◽  
Delay Times

Laminar flame speeds and ignition delay times have been measured for hydrogen and various compositions of H2/CO (syngas) at elevated pressures and elevated temperatures. Two constant-volume cylindrical vessels were used to visualize the spherical growth of the flame through the use of a schlieren optical setup to measure the laminar flame speed of the mixture. Hydrogen experiments were performed at initial pressures up to 10 atm and initial temperatures up to 443 K. A syngas composition of 50/50 by volume was chosen to demonstrate the effect of carbon monoxide on H2-O2 chemical kinetics at standard temperature and pressures up to 10 atm. All atmospheric mixtures were diluted with standard air, while all elevated-pressure experiments were diluted with a He:O2 ratio of 7:1 to minimize instabilities. The laminar flame speed measurements of hydrogen and syngas are compared to available literature data over a wide range of equivalence ratios, where good agreement can be seen with several data sets. Additionally, an improved chemical kinetics model is shown for all conditions within the current study. The model and the data presented herein agree well, which demonstrates the continual, improved accuracy of the chemical kinetics model. A high-pressure shock tube was used to measure ignition delay times for several baseline compositions of syngas at three pressures across a wide range of temperatures. The compositions of syngas (H2/CO) by volume presented in this study included 80/20, 50/50, 40/60, 20/80, and 10/90, all of which are compared to previously published ignition delay times from a hydrogen-oxygen mixture to demonstrate the effect of carbon monoxide addition. Generally, an increase in carbon monoxide increases the ignition delay time, but there does seem to be a pressure dependency. At low temperatures and pressures higher than about 12 atm, the ignition delay times appear to be indistinguishable with an increase in carbon monoxide. However, at high temperatures the relative composition of H2 and CO has a strong influence on ignition delay times. Model agreement is good across the range of the study, particularly at the elevated pressures.

scholarly journals Laminar flame speed of soy and canola biofuels

2012 ◽  
Vol 4 (5) ◽  
pp. 75-83 ◽  
Author(s):  
Juan-Sebastián Gómez-Meyer ◽  
Subramanyam R Gollahalli ◽  
Ramkumar N. Parthasarathy ◽  
Jabid-Eduardo Quiroga
Keyword(s):  
Flame Propagation ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Thermochemical Property ◽  
Laminar Flame Speed ◽  
Hot Air ◽  
Maximum Value ◽  
Canola Oils

In this article, the flame speed values determined experimentally for laminar premixed flames of the vapors of two biofuels in air are presented. The laminar flame speed is a fundamental thermochemical property of fuels, and is essential for analyzing the flame propagation in practical devices, even those employing turbulent flames. The fuels obtained from transesterification of soy and canola oils are tested. Also, the diesel flames are studied to serve as a baseline for comparison. The experiments are performed with a tubular burner; pre-vaporized fuel is mixed with hot air and is ignited. The flame speed is determined at fuel-equivalence ratios of 1; 1,1 and 1,2 by recording the geometry of the flame. The experimental results show that the flame speed of biofuels is lower by about 15% than that of diesel. Also, the maximum value of flame speed is obtained at an equivalence ratio of approximately 1,1.

Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Brendan Shaffer ◽  
Zhixuan Duan ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Fuel Composition ◽  
Laminar Flame Speed ◽  
Processing Scheme ◽  
High Hydrogen ◽  
Jet Flame ◽  
Wide Range

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15–100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700 K and 1900 K. Once a flame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was used.

Flashback Limits of Premixed H2/CH4 Flames in a Swirl-Stabilized Combustor

2010 ◽  
Author(s):  
Nasser Shelil ◽  
Anthony Griffiths ◽  
Audrius Bagdanavicius ◽  
Nick Syred
Keyword(s):  
Atmospheric Pressure ◽  
Laminar Flame ◽  
Flame Speed ◽  
Cfd Modeling ◽  
Pure Hydrogen ◽  
Laminar Flame Speed ◽  
Operating Pressure ◽  
Mixture Ratio ◽  
Fuel Blends ◽  
Pure Methane

CFD modeling is used to simulate the combustion and flashback behavior of H2/CH4 fuel blends with air in a premixed swirl burner using a three dimensional–finite volume model. Preliminary work was performed to calculate the laminar flame speed for H2/CH4 blends from pure methane up to pure hydrogen at various pressures, temperatures and equivalence ratios by using CHEMKIN, for pure fuels, and a new approximation based on the gravimetric mixture ratio, for the fuel blends. Then, the numerical values for laminar flame speed were fed to a FLUENT CFD model to create a PDF table for turbulent premixed combustion calculations and flashback studies. Flashback limits were defined and determined for H2/CH4 blends ranging from 0% (pure methane) up to 100% (pure hydrogen) based on the volumetric composition at atmospheric pressure and 300K for various equivalence ratios. The simulations were compared with experimental measurements at atmospheric pressure for two fuel blends with γ of 0.15 and 0.3 and showed best fit for equivalence ratios less than 0.75 to 0.8. The work was then extended to include simulation studies to investigate the effect of operating pressure and raw gases temperature on flame stability and showed a high dependence on both operating pressure and raw gases temperature.

Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner

2012 ◽  
Author(s):  
Brendan Shaffer ◽  
Zhixuan Duan ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Fuel Composition ◽  
Laminar Flame Speed ◽  
Processing Scheme ◽  
High Hydrogen ◽  
Jet Flame ◽  
Wide Range

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15–100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700 K and 1900 K. Once a flame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was used.

An Investigation on Laminar Flame Speed as Part of Needed Combustion Characteristics of Biomass-Based Syngas Fuels

2007 ◽  
Author(s):  
Marina Braun-Unkhoff ◽  
Thomas Kick ◽  
Peter Frank ◽  
Manfred Aigner
Keyword(s):  
Reaction Mechanisms ◽  
Co2 Sequestration ◽  
Alternative Fuels ◽  
Laminar Flame ◽  
Gas Mixtures ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Hydrogen Burning ◽  
Biogenic Gas ◽  
Wide Range

The present work reports on laminar flame speed measurements with biogenic gas mixtures over a wide range of parameters, such as preheat temperatures, pressure, equivalence ratio, and gas compositions. The biogenic gas mixtures were derived from gasification of ethanol and of corn silage as representatives for alternative fuels containing hydrogen and methane as major components (after CO2-sequestration), light hydrocarbons to some extent, and diluents such as nitrogen and carbon monoxide. In the present work, premixed flames were stabilized in a high pressure burner system at pressures up to 6 bars at preheat temperatures between 323 and 453 K and for equivalence ratios of φ = 0.5–1.6. In addition, a gas mixture of methane and hydrogen burning in air was investigated at atmospheric pressure. Furthermore, different detailed reaction mechanisms were used to predict the measured data. The trends and main features were captured by predictions applying different reaction mechanisms.

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