A Reduced Kinetic Mechanism for Oxy/Methane sCO2 Combustor Simulations

2018 ◽  
Author(s):  
K. R. V. Manikantachari ◽  
Ladislav Vesely ◽  
Scott Martin ◽  
Jose O. Bobren-Diaz ◽  
Subith Vasu
Keyword(s):  
Ignition Delay ◽  
Ignition Delay Time ◽  
High Pressures ◽  
Fluid Dynamic ◽  
Kinetic Mechanism ◽  
Flux Analysis ◽  
Analysis Method ◽  
Stirred Reactor ◽  
Ignition Delay Times ◽  
Delay Times

Reduced mechanisms are needed for use with computational fluid dynamic codes (CFD) utilized in the design of combustors. Typically, the reduced mechanisms are created from the detailed mechanisms which contain numerous species and reactions that are computationally difficult to handle using most CFD codes. Recently, it has been shown that the detailed Aramco 2.0 mechanism well predicted the available experimental data at high pressures and in high-CO2 diluted methane mixtures. Further, a 23-species gas-phase mechanism is derived from the detailed Aramco 2.0 mechanism by path-flux-analysis method (PFA) by using CHEM-RC. It is identified that the reaction CH4+HO2⇔ CH3+H2O2 is very crucial in predicting the ignition delay times under current conditions. Further, it is inferred that species C2H3 and CH3OH are very important in predicting the ignition delay time of lean sCO2 methane mixtures. Also, the 23-species mechanism presented in this work is performing on par with the detailed Aramco 2.0 mechanism in-terms of simulating ignition delay times, perfectly-stirred-reactor estimates under various CO2 dilutions and equivalence ratios, and prediction of turbulence chemistry interactions. It is observed that the choice of equation-of-state has no significant impact on the ignition delay times of supercritical CH4/O2/CO2 mixtures but it influences supercritical H2/O2/CO2 mixtures considered in this work.

Reduced Chemical Kinetic Mechanisms for Oxy/Methane Supercritical CO2 Combustor Simulations

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
K. R. V. Manikantachari ◽  
Ladislav Vesely ◽  
Scott Martin ◽  
Jose O. Bobren-Diaz ◽  
Subith Vasu
Keyword(s):  
Gas Phase ◽  
High Pressures ◽  
Fluid Dynamic ◽  
Chemical Kinetic ◽  
Flux Analysis ◽  
Analysis Method ◽  
Stirred Reactor ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Kinetic Mechanisms

Reduced mechanisms are needed for use with computational fluid dynamic codes (CFD) utilized in the design of combustors. Typically, reduced mechanisms are created from a detailed mechanism, which contain numerous species and reactions that are computationally difficult to handle using most CFD codes. Recently, it has been shown that the detailed aramco 2.0 mechanism well predicted the available experimental data at high pressures and in highly CO2 diluted methane mixtures. Here, a 23-species gas-phase mechanism is derived from the detailed aramco 2.0 mechanism by path-flux-analysis method (PFA) by using CHEM-RC. It is identified that the reaction CH4 + HO2 ⇔ CH3 + H2O2 is very crucial in predicting the ignition delay times (IDTs) under current conditions. Further, it is inferred that species C2H3 and CH3OH are very important in predicting IDTs of lean sCO2 methane mixtures. Also, the 23-species mechanism presented in this work is able to perform on par with the detailed aramco 2.0 mechanism in terms of simulating IDTs, perfectly stirred-reactor (PSR) estimates under various CO2 dilutions and equivalence ratios, and prediction of turbulence chemistry interactions. It is observed that the choice of equation of state has no significant impact on the IDTs of supercritical CH4/O2/CO2 mixtures but it influences supercritical H2/O2/CO2 mixtures considered in this work.

Ignition Characteristics of a Fischer-Tropsch Synthetic Jet Fuel

2008 ◽  
Author(s):  
P. Gokulakrishnan ◽  
M. S. Klassen ◽  
R. J. Roby
Keyword(s):  
Kinetic Model ◽  
Ignition Delay ◽  
Flow Reactor ◽  
Kinetic Mechanism ◽  
Jet Fuel ◽  
Synthetic Jet ◽  
Jet Fuels ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Ignition Characteristics

Ignition delay times of a “real” synthetic jet fuel (S8) were measured using an atmospheric pressure flow reactor facility. Experiments were performed between 900 K and 1200 K at equivalence ratios from 0.5 to 1.5. Ignition delay time measurements were also performed with JP8 fuel for comparison. Liquid fuel was prevaporized to gaseous form in a preheated nitrogen environment before mixing with air in the premixing section, located at the entrance to the test section of the flow reactor. The experimental data show shorter ignition delay times for S8 fuel than for JP8 due to the absence of aromatic components in S8 fuel. However, the ignition delay time measurements indicate higher overall activation energy for S8 fuel than for JP8. A detailed surrogate kinetic model for S8 was developed by validating against the ignition delay times obtained in the present work. The chemical composition of S8 used in the experiments consisted of 99.7 vol% paraffins of which approximately 80 vol% was iso-paraffins and 20% n-paraffins. The detailed kinetic mechanism developed in the current work included n-decane and iso-octane as the surrogate components to model ignition characteristics of synthetic jet fuels. The detailed surrogate kinetic model has approximately 700 species and 2000 reactions. This kinetic mechanism represents a five-component surrogate mixture to model generic kerosene-type jets fuels, namely, n-decane (for n-paraffins), iso-octane (for iso-paraffins), n-propylcyclohexane (for naphthenes), n-propylbenzene (for aromatics) and decene (for olefins). The sensitivity of iso-paraffins on jet fuel ignition delay times was investigated using the detailed kinetic model. The amount of iso-paraffins present in the jet fuel has little effect on the ignition delay times in the high temperature oxidation regime. However, the presence of iso-paraffins in synthetic jet fuels can increase the ignition delay times by two orders of magnitude in the negative temperature (NTC) region between 700 K and 900 K, typical gas turbine conditions. This feature can have a favorable impact on preventing flashback caused by the premature autoignition of liquid fuels in lean premixed prevaporized (LPP) combustion systems.

Interpretation of Flow Reactor Based Ignition Delay Measurements

2009 ◽  
Author(s):  
David Beerer ◽  
Vincent McDonell ◽  
Scott Samuelsen ◽  
Leonard Angello
Keyword(s):  
High Pressure ◽  
Gas Turbine ◽  
Residence Time ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Flow Reactor ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Recirculation Zones

Compositional variation of global gas supplies is becoming a growing concern. Both the range and rate-of-change of this variation is expected to increase as global markets for Liquefied Natural Gas (LNG) continue to expand. Greater fuel composition variation poses increased operational risk to gas turbine engines employing lean premixed combustion systems. Information on ignition delay at high pressure and intermediate temperatures is valuable for lean premixed gas turbine design. In order to avoid autoignition of the fuel/air mixture within the premixer, the ignition delay time must be greater than the residence time. Evaluating the residence time is not a straight forward task because of the complex aerodynamics due to recirculation zones, separation regions, and boundary layers effects which may create regions where the local residence times may be longer than the bulk or average residence time. Additionally, reliable experiments on ignition delay at gas turbine conditions are difficult to conduct. Devices for testing include shock tubes, rapid compression machine and flow reactors. In a flow reactor ignition delay data are commonly determined by measuring the distance from the fuel injector to the reaction front (L) and dividing it by the bulk or average flow velocity (U) under steady flow conditions to obtain a bulk residence time which is assumed to be equal to the ignition delay time. However this method is susceptible to the same boundary layer effects or recirculation zones found in premixers. An alternative method for obtaining ignition delay data in a flow reactor is presented herein, where ignition delay times are obtained by measuring the time difference between fuel injection and ignition using high speed instrumentation. Ignition delay times for methane, ethane and propane at gas turbine conditions were in the range of 40–500 ms. The results obtained show excellent agreement with recently proposed chemical mechanisms for hydrocarbons at low temperature/high pressure conditions.

Experimental Study and Modeling of Autoignition of Natural Gas/Air-Mixtures Under Gas Turbine Relevant Conditions

2005 ◽  
Author(s):  
Andreas Koch ◽  
Clemens Naumann ◽  
Wolfgang Meier ◽  
Manfred Aigner
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Ignition Delay ◽  
Delay Time ◽  
High Speed ◽  
Ignition Delay Time ◽  
Evaluation Procedure ◽  
Ignition Process ◽  
Ignition Delay Times ◽  
Delay Times

The objective of this work was the improvement of methods for predicting autoignition in turbulent flows of different natural gas mixtures and air. Measurements were performed in a mixing duct where fuel was laterally injected into a turbulent flow of preheated and pressurized air. To study the influence of higher order hydrocarbons on autoignition, natural gas was mixed with propane up to 20% by volume at pressures up to 15 bar. During a measurement cycle, the air temperature was increased until autoignition occurred. The ignition process was observed by high-speed imaging of the flame chemiluminescence. In order to attribute a residence time (ignition delay time) to the locations where autoignition was detected the flow field and its turbulent fluctuations were simulated by numerical codes. These residence times were compared to calculated ignition delay times using detailed chemical simulations. The measurement system and data evaluation procedure are described and preliminary results are presented. An increase in pressure and in fraction of propane in the natural gas both reduced the ignition delay time. The measured ignition delay times were systematically longer than the predicted ones for temperatures above 950 K. The results are important for the design process of gas turbine combustors and the studies also demonstrate a procedure for the validation of design tools under relevant conditions.

Ignition Delay Times of Syngas and Methane in sCO2 Diluted Mixtures for Direct-Fired Cycles

2019 ◽  
Author(s):  
Samuel Barak ◽  
Owen Pryor ◽  
Erik Ninnemann ◽  
Sneha Neupane ◽  
Xijia Lu ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Ignition Delay ◽  
High Pressures ◽  
Chemical Kinetic ◽  
Time Data ◽  
Fuel Loading ◽  
Supercritical Regime ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Delay Times

Abstract In this study, a shock tube is used to investigate combustion tendencies of several fuel mixtures under high carbon dioxide dilution and high fuel loading. Individual mixtures of oxy-syngas and oxy-methane fuels were added to CO2 bath gas environments and ignition delay time data was recorded. Reflected shock pressures maxed around 100 atm, which is above the critical pressure of carbon dioxide in to the supercritical regime. In total, five mixtures were investigated within a temperature range of 1050–1350K. Ignition delay times of all mixtures were compared with predictions of two leading chemical kinetic computer mechanisms for accuracy. The mixtures included four oxy-syngas and one oxy-methane combinations. The experimental data tended to show good agreement with the predictions of literature models for the methane mixture. For all syngas mixtures though the models performed reasonably well at some conditions, predictions were not able to accurately capture the overall behavior. For this reason, there is a need to further investigate the discrepancies in predictions. Additionally, more data must be collected at high pressures to fully understand the chemical kinetic behavior of these mixtures to enable the supercritical CO2 power cycle development.

Ignition Delay Times of High Pressure Oxy-Methane Combustion With High Levels of CO2 Dilution

2017 ◽  
Author(s):  
Owen Pryor ◽  
Batikan Koroglu ◽  
Samuel Barak ◽  
Joseph Lopez ◽  
Erik Ninnemann ◽  
...  
Keyword(s):  
Shock Tube ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Current Data ◽  
Validation Data ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Kinetic Mechanisms ◽  
Time Histories

Ignition delay times and methane species time-histories were measured for methane/O2 mixtures in a high CO2 diluted environment using shock tube and laser absorption spectroscopy. The experiments were performed between 1300 K and 2000 K at pressures between 1 and 31 atm. The experimental mixtures were conducted at an equivalence ratio of 1 with CH4 mole fractions ranging from 3.5%–5% and up to 85% CO2 with a bath of argon gas as necessary. The ignition delay times and methane time histories were measured using pressure, emission, and laser diagnostics. Predictive ability of two literature kinetic mechanisms (GRI 3.0 and ARAMCO Mech 1.3) was tested against current data. In general, both mechanisms performed reasonably well against ignition delay time data. The methane time-histories showed good agreement with the mechanisms for most of the conditions measured. A correlation for ignition delay time was created taking into the different parameters showing that the ignition activation energy for the fuel to be 49.64 kcal/mol. Through a sensitivity analysis, CO2 is shown to slow the overall reaction rate and increase the ignition delay time. To the best of our knowledge, we present the first shock tube data during ignition of methane under these conditions. Current data provides crucial validation data needed for development of future methane/CO2 kinetic mechanisms.

scholarly journals High-Speed Imaging and Measurements of Ignition Delay Times in Oxy-Syngas Mixtures With High CO2 Dilution in a Shock Tube

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Samuel Barak ◽  
Owen Pryor ◽  
Joseph Lopez ◽  
Erik Ninnemann ◽  
Subith Vasu ◽  
...  
Keyword(s):  
Shock Tube ◽  
Ignition Delay ◽  
Delay Time ◽  
High Speed ◽  
Ignition Delay Time ◽  
High Speed Imaging ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Syngas Combustion ◽  
End Wall

In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% to 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios (ϕ), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio (θ), hydrogen to carbon monoxide, from 0.25, 1.0, and 4.0. The study was performed at 1.61–1.77 atm and a temperature range of 1006–1162 K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed nonhomogeneous combustion in the system; however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.

scholarly journals The influence of n -butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

Fuel ◽  
2017 ◽  
Vol 187 ◽  
pp. 211-219 ◽  
Author(s):  
Edirin Agbro ◽  
Alison S. Tomlin ◽  
Malcolm Lawes ◽  
Sungwoo Park ◽  
S. Mani Sarathy
Keyword(s):  
Ignition Delay ◽  
High Pressures ◽  
Ignition Delay Times ◽  
Delay Times

A Study of Methane and Hydrogen Ignition Delay Times in CO2 at High Pressures Near 40 atm

2018 ◽  
Author(s):  
Samuel Barak ◽  
Erik M. Ninnemann ◽  
Sneha Neupane ◽  
Frank Barnes ◽  
Subith Vasu
Keyword(s):  
Ignition Delay ◽  
High Pressures ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Hydrogen Ignition
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