Multistage auto-ignition of undiluted methane/air mixtures under engine-relevant condition

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Yingjia Zhang ◽  
Wuchuan Sun ◽  
Wenlin Huang ◽  
Xiaokang Qin ◽  
Jinshu Liu ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Shock Tube ◽  
Oh Radicals ◽  
Ignition Process ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Kinetic Mechanisms ◽  
Perform Sensitivity Analysis ◽  
The Difference

Gas-phase auto-ignition delay times (IDTs) of methane/“air” (21% O2/79% Ar) mixtures were measured behind reflected shock waves, using a kinetic shock tube. Experiments were performed at fixed pressure of 1.8 MPa and equivalence ratios of 0.5 and 1.0, over the temperature range of 800–1000 K. Overall, the effect of equivalence ratio on IDT is negligible at entire temperatures measured in this study. The difference from traditional ignition regime at high temperatures, the undiluted methane/air mixtures present a four-stage ignition process at lower temperatures, namely deflagration delay, deflagration, deflagration-detonation transition, and detonation. Four popular kinetic mechanisms, UBC Mech 2.1, GRI Mech 3.0, Aramco Mech 2.0, and USC Mech 2.0, were used to simulate the new measurements. Only UBC Mech 2.1 showed satisfactory predictions in the reactivity of the undiluted methane mixtures; it was, thus, adopted to perform sensitivity analysis for identifying dominant reactions in the ignition process. The difference in channels contributing ȮH radicals causes a reduced global activation energy with decreasing temperatures.Keywords: Methane; multistage ignition; shock tube; sensitivity analysis

The Shock Tube Autoignition of Biodiesels and Biodiesel Components

2013 ◽  
Author(s):  
Weijing Wang ◽  
Matthew A. Oehlschlaeger
Keyword(s):  
High Temperature ◽  
Methyl Ester ◽  
Shock Tube ◽  
Ignition Delay ◽  
Methyl Esters ◽  
Acid Methyl Ester ◽  
Oh Radicals ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Delay Times

The autoignition of fatty-acid methyl ester biodiesels and methyl ester biodiesel components was studied in gas-phase shock tube experiments. Ignition delay times for two reference methyl ester biodiesel fuels, derived from methanol-based transesterification of soybean oil and animal fats, and four primary constituents of all methyl ester biodiesels, methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate, were measured behind reflected shock waves for fuel/air mixtures at temperatures ranging from 900 to 1350 K and at pressures around 10 and 20 atm. Ignition delay times were determined by monitoring pressure and chemiluminescence from electronically-excited OH radicals around 310 nm. The results show similarity in ignition delay times for all methyl ester fuels considered, irrespective of the variations in organic structure, at the high-temperature conditions studied and also similarity in high-temperature ignition delay times for methyl esters and n-alkanes.

High-Pressure Oxy-Syngas Ignition Delay Times With CO2 Dilution: Shock Tube Measurements and Comparison of the Performance of Kinetic Mechanisms

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Samuel Barak ◽  
Erik Ninnemann ◽  
Sneha Neupane ◽  
Frank Barnes ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Experimental Data ◽  
Shock Tube ◽  
Ignition Delay ◽  
Current Data ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Syngas Combustion ◽  
Kinetic Mechanisms ◽  
Data Points

In this study, syngas combustion was investigated behind reflected shock waves in CO2 bath gas to measure ignition delay times (IDT) and to probe the effects of CO2 dilution. New syngas data were taken between pressures of 34.58–45.50 atm and temperatures of 1113–1275 K. This study provides experimental data for syngas combustion in CO2 diluted environments: ignition studies in a shock tube (59 data points in 10 datasets). In total, these mixtures covered a range of temperatures T, pressures P, equivalence ratios φ, H2/CO ratio θ, and CO2 diluent concentrations. Multiple syngas combustion mechanisms exist in the literature for modeling IDTs and their performance can be assessed against data collected here. In total, twelve mechanisms were tested and presented in this work. All mechanisms need improvements at higher pressures for accurately predicting the measured IDTs. At lower pressures, some of the models agreed relatively well with the data. Some mechanisms predicted IDTs which were two orders of magnitudes different from the measurements. This suggests that there is behavior that has not been fully understood on the kinetic models and is inaccurate in predicting CO2 diluted environments for syngas combustion. To the best of our knowledge, current data are the first syngas IDTs measurements close to 50 atm under highly CO2 diluted (85% per vol.) conditions.

High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils

2021 ◽  
Author(s):  
Sean P. Cooper ◽  
Eric Petersen
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Shock Tube ◽  
Gas Turbine ◽  
Temperature Regime ◽  
Negative Temperature ◽  
Ignition Process ◽  
Reflected Shock ◽  
Driver Gas ◽  
Auto Ignition

Abstract Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (tign). An extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage tign are compared. The secondary ignition was found to be more indicative of combustion and was used to compare tign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (>1275 K); an intermediate, negative-temperature-coefficient-like regime (1230-1275 K); and a low-temperature ignition regime (<1230 K). Lubricant A was found to be less reactive in the intermediate-temperature regime, but Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation.

scholarly journals Aerosol Shock Tube Designed for Ignition Delay Time Measurements of Low-Vapor-Pressure Fuels and Auto-Ignition Flow-Field Visualization

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 683
Author(s):  
Erwei Liu ◽  
Qin Liao ◽  
Shengli Xu
Keyword(s):  
Flow Field ◽  
Vapor Pressure ◽  
Shock Tube ◽  
Ignition Delay ◽  
Pressure Sensors ◽  
Local Pressure ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Delay Times ◽  
Sequential Images

An aerosol shock tube has been developed for measuring the ignition delay times (tig) of aerosol mixtures of low-vapor-pressure fuels and for visualization of the auto-ignition flow-field. The aerosol mixture was formed in a premixing tank through an atomizing nozzle. Condensation and adsorption of suspended droplets were not observed significantly in the premixing tank and test section. A particle size analyzer was used to measure the Sauter mean diameter (SMD) of the aerosol droplets. Three pressure sensors and a photomultiplier were used to detect local pressure and OH emission respectively. Intensified charge-coupled device cameras were used to capture sequential images of the auto-ignition flow-field. The results indicated that stable and uniform aerosol could be obtained by this kind of atomizing method and gas distribution system. The averaged SMD for droplets of toluene ranged from 2 to 5 μ m at pressures of 0.14–0.19 MPa of dilute gases. In the case of a stoichiometric mixture of toluene/O2/N2, ignition delay times ranged from 77 to 1330 μs at pressures of 0.1–0.3 MPa, temperatures of 1432–1716 K and equivalence ratios of 0.5–1.5. The logarithm of ignition delay times was approximately linearly correlated to 1000/T. In contrast to the reference data, ignition delay times of aerosol toluene/O2/N2 were generally larger. Sequential images of auto-ignition flow-field showed the features of flame from generation to propagation.

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.

High Pressure Ignition of Boron in Reduced Oxygen Atmospheres

1995 ◽  
Vol 418 ◽  
Author(s):  
R. O. Foelsche ◽  
M. J. Spalding ◽  
R. L. Burton ◽  
H. Krier
Keyword(s):  
High Pressure ◽  
Water Vapor ◽  
Shock Tube ◽  
Ignition Delay ◽  
Peak Pressure ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Fluorine Compounds ◽  
Delay Times ◽  
Tube Study

AbstractBoron ignition delay times for 24 μm diameter particles have been measured behind the reflected shock at a shock tube endwall in reduced oxygen atmospheres and in a combustion bomb at higher pressures in the products of a hydrogen/oxygen/nitrogen reaction. The shock tube study independently varies temperature (1400 – 3200 K), pressure (8.5, 34 atm), and ignition-enhancer additives (water vapor, fluorine compounds). A combustion chamber is used at a peak pressure of 157 atm and temperature in excess of 2800 K to study ignition delays at higher pressures than are possible in the shock tube.

Shock Tube Studies of the Reactions of Hydrogen Atoms. I. The Reaction H + NH3 → H2 + NH2

1974 ◽  
Vol 52 (7) ◽  
pp. 1171-1180 ◽  
Author(s):  
John E. Dove ◽  
Wing S. Nip
Keyword(s):  
Shock Tube ◽  
Rate Coefficients ◽  
Oh Radicals ◽  
High Concentration ◽  
Hydrogen Atoms ◽  
Elementary Reactions ◽  
Temperature Range ◽  
Reflected Shock ◽  
Branched Chain ◽  
Chain Explosion

The partial equilibrium state following the branched-chain explosion of shock-heated rich H2/O2/diluent mixtures contains a high concentration of H atoms. The conditions under which this state can be used as a source of H atoms for the study of elementary reactions have been investigated. A small amount of NH3 was added to H2/O2/inert gas mixtures in order to measure the rate of the reaction H + NH3 → H2 + NH2. The pseudo-first order decay of NH3 in an approximately ten-fold excess of H atoms was followed by a time-of-flight mass spectrometer which sampled from the reflected shock region in a shock tube. The rate coefficient for this reaction, determined over the temperature range 1500–2150 °K, is 1013.44±0.10 exp −(17 400 ± 1 300 cal mol−1)/RT cm3 mol−1 s−1.It is pointed out that, under certain stated conditions, the method can also be extended to study the rates of elementary reactions involving O atoms and OH radicals. From our experiments, upper limits on the rate coefficients of the reactions OH + NH3 → H2O + NH2 and O + NH3 → OH + NH2 over the temperature range 1620–1920 °K are 8 × 109T0.08 exp (−1100/RT) and 1 × 1013 exp (−6600/RT), respectively.

scholarly journals Development of a Model for Auto-Ignition Delays and its Use for the Prediction of Premix Combustion Reliability

2016 ◽  
Author(s):  
Roda Bounaceur ◽  
Pierre-Alexandre Glaude ◽  
Baptiste Sirjean ◽  
René Fournet ◽  
Pierre Montagne ◽  
...  
Keyword(s):  
Ignition Delay ◽  
Equivalence Ratio ◽  
Fuel Mixture ◽  
Fuel Composition ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Wide Range ◽  
Kinetic Mechanisms ◽  
Safety And Reliability ◽  
Low Nox Combustion

Except in diesel engine applications, auto-ignition is an unwanted event from a general safety and reliability standpoint. It is especially undesirable in the premixing process involved in most low NOx combustion technologies. Therefore, in addition to auto-ignition temperature, autoignition delay (AID) is a key data for the design of modern combustors including gas turbine ones. The authors have investigated the detailed kinetic mechanisms leading to autoignition and established practical AID correlations involving the fuel composition, its temperature, pressure and equivalence ratio. The correlations brought about during this program offer a good reconciliation between calculated and experimental AID through a wide range of fuel composition, initial temperature and pressure. Validations were mainly done against data acquired with experimental setups consisting in shock tubes and rapid compression machines. The auto-ignition delay times of methane, pure light alkanes and various blends representative of several natural gas and process-derived fuels have been reviewed. For each fuel mixture, this study procures a simple equation linking the auto-ignition delay time to the temperature, pressure and equivalence ratio. As a direct application of this work, the authors have evaluated the risk of auto ignition in the premixing zone of a combustor characterized by a residence time and an associated probability density function. The results of this simulation stress the key role of larger hydrocarbon in the risk of flash-back events.

Auto-Ignition of Gas Turbine Lubricating Oils in a Shock Tube Using Spray Injection

2021 ◽  
Author(s):  
Sean P. Cooper ◽  
Zachary K. Browne ◽  
Sulaiman A. Alturaifi ◽  
Olivier E. Mathieu ◽  
Eric Petersen
Keyword(s):  
Shock Tube ◽  
Gas Turbine ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Lubricating Oil ◽  
Fuel Injector ◽  
Lubricating Oils ◽  
Reflected Shock ◽  
Auto Ignition

Abstract In choosing the lubricating oil for a gas turbine system, properties such as viscosity, viscosity index, corrosion prevention, and thermal stability are chosen to optimize turbine longevity and efficiency. Another property that needs to be considered is the lubricant's reactivity, as the lubricant's ability to resist combustion during turbine operation is highly desirable. In evaluating a method to define reactivity, the extremely low vapor pressure of these lubricants makes conventional vaporization by heating impractical. To this end, a new experiment was designed and tested to evaluate the reactivity of lubricating oils using an existing shock-tube facility at Texas A&M University equipped with an automotive fuel injector. This experiment disperses a pre-measured amount of lubricant into a region of high-temperature air to study auto-ignition. To ensure proper dispersal, a laser extinction diagnostic was used to detect the lubricant particles behind the reflected shock as they are dispersed and vaporized. An OH* chemiluminescence diagnostic was used to determine ignition delay time. Using this method, various 32-, 36-, and 46-weight lubricants identified as widely used in the gas turbine industry were tested. Experiments were conducted in post-reflected shock conditions around 1370 K (2006 ºF) and 1.2 atm, where ignition delay time, peak OH* emission, and time-to-peak values were recorded and compared. Ignition was observed for all but one of the lubricants at these conditions, and mild to strong ignition was observed for the other lubricants with varying ignition delay times.

scholarly journals Numerical Investigation of Remote Ignition in Shock Tubes

2020 ◽  
Author(s):  
Jonathan Timo Lipkowicz ◽  
Damien Nativel ◽  
Sean Cooper ◽  
Irenäus Wlokas ◽  
Mustapha Fikri ◽  
...  
Keyword(s):  
Shock Tube ◽  
Three Dimensional ◽  
Wall Region ◽  
Ignition Process ◽  
Computational Domain ◽  
Shock Attenuation ◽  
Link Type ◽  
Reflected Shock ◽  
Computational Fluid Dynamics Cfd ◽  
End Wall

Abstract Highly resolved two- and three-dimensional computational fluid dynamics (CFD) simulations are presented for shock-tube experiments containing hydrogen/oxygen (H2/O2) mixtures, to investigate mechanisms leading to remote ignition. The results of the reactive cases are compared against experimental results from Meyer and Oppenheim (Proc Combust Inst 13(1): 1153–1164, 1971. 10.1016/s0082-0784(71)80112-1) and Hanson et al. (Combust Flame 160(9): 1550–1558, 2013. 10.1016/j.combustflame.2013.03.026). The results of the non-reactive case are compared against shock tube experiments, recently carried out in Duisburg and Texas. The computational domain covers the end-wall region of the shock tube and applies high order numerics featuring an all-speed approximate Riemann scheme, combined with a 5th order interpolation scheme. Direct chemistry is employed using detailed reaction mechanisms with 11 species and up to 40 reactions, on a grid with up to 2.2 billion cells. Additional two-dimensional simulations are performed for non-reactive conditions to validate the treatment of boundary-layer effects at the inlet of the computational domain. The computational domain covers a region at the end part of the shock tube. The ignition process is analyzed by fields of localized, expected ignition times. Instantaneous fields of temperature, pressure, entropy, and dissipation rate are presented to explain the flow dynamics, specifically in the case of a bifurcated reflected shock. In all cases regions with locally increased temperatures were observed, reducing the local ignition-delay time in areas away from the end wall significantly, thus compensating for the late compression by the reflected shock and therefore leading for first ignition at a remote location, i.e., away from the end wall where the ignition would occur under ideal conditions. In cases without a bifurcated reflected shock, the temperature increase results from shock attenuation. In cases with a bifurcated reflected shock, the formation of a second normal shock and shear near the slip line is found to be crucial for the remote ignition to take place. Overall, the two- and three-dimensional simulations were found to qualitatively explain the occurrence of remote ignition and to be quantitatively correct, implying that they include the correct physics.

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