Blowout Conditions Research Articles

Advanced multiscale modal and frequency analysis of swirling spray flame near to lean blowout

This study provides an in-depth characterization of Jet-A1 swirled flames' dynamics using advanced decomposition techniques on high-speed OH* chemiluminescence images. Research conducted in a 300-kW combustor with global fuel-to-air ratios Φ = 0.36, 0.24, and 0.18 reveals dominant low-frequency components under ultra-lean conditions through statistical and wavelet analyses. Integrating Proper Orthogonal Decomposition (POD), Dynamic Mode Decomposition (DMD), and Multiscale Proper Orthogonal Decomposition (mPOD) enhances understanding by detailing the energy and frequency of flame modal structures. Observations show that as Φ decreases, flame size and intensity reduce, while fluctuations increase, indicating a transition towards unstable combustion dynamics. Furthermore, the frequency and intensity of burst phenomena increase, particularly in higher modes, indicating the system's approach to lean blowout (LBO). The application of nonlinear time series analysis, including autocorrelation (AFC) and phase space reconstruction, to mPOD eigenvalues, detects early warning signs of LBO. At lower Φ, the ACF reveals significant and frequent bursts, indicating high instability and intermittent behavior. Phase space reconstruction shows distorted orbits with a spiral-like structure, characteristic of substantial damping and irregular behavior near blowout conditions.

Gas-Flow-Rate Inversion Based on Experiments and Simulation of Flame Combustion Characteristics in a Drilling Blowout

Accurately estimating the gas-flow rate at a wellhead to invert the formation pressure and production capacity information can be the basis for subsequent well-killing parameter design following oil and gas-well drilling blowout and ignition. Based on the multicomponent characteristics of the blowout gas and the turbulence intensity of the blowout flame, as well as the effects of complex factors such as environmental wind direction, wind speed, and wellhead structure, a numerical model for actual drilling blowout ignition is established. Jet-flame experiments are conducted under blowout conditions to verify the accuracy of the model. The temperature and radiation fields and flame morphologies of the well jet flow flame under different lateral wind speeds, well jet flow rates, and wellhead diameters are analyzed. Previous studies have found that as the lateral wind speed increases, the maximum temperature and maximum thermal radiation intensity of the blowout flame first decrease and then increase. However, as the amount of well jet increases, although the flame influence area increases, the maximum temperature does not increase significantly, and the maximum thermal radiation intensity actually decreases. Based on experimental and numerical simulation datasets, a high-yield gas-well jet volume prediction method based on the flame height and thermal radiation intensity of the well jet flow is constructed, which has important engineering application value for achieving successful well killing following well jet ignition.

Characteristics of laminar lifted flames of pure ethane in a non-premixed jet under various pressures

Recent studies have discovered that laminar lifted flames (LLFs) can be stabilized within a triangular stabilization regime (TSR), defined by the parameters of normalized lift-off height and Reynolds number. The stabilization mechanism of an LLF could be explained by using an effective Schmidt number over an extended pressure range. In this study, the existence of LLFs of pure ethane was confirmed for the first time, and their characteristics were investigated. However, the corresponding TSR was significantly shrunk compared to propane and butane. The reasons were discussed in relation to the effective Schmidt number. The variation in effective Schmidt number depending on lift-off height and fuel type was theoretically predicted by considering the relative influence of the volume expansion on flow velocity and fuel concentration. Two additional stabilization modes near the turbulent transition were examined. One is the pathway from LLFs within the TSR to turbulent lifted flames at higher Reynolds numbers, and the criteria for this transition were explained. The other is an additional stabilization mode having much larger lift-off heights near the blowout conditions, and its stabilization mechanism was discussed.

Model predictive control for three-axle trucks during tire blowout on expressway based on equivalent chassis

Unexpected tire blowout on expressway is one of the most dangerous scenarios for heavy load multi-axle trucks, especially under the inexperienced driver’s improper intervention. To this end, this paper proposes an autonomous tire blowout controller for three-axle trucks based on model predictive control (MPC) method. First of all, aiming at balancing the computing load and the path-tracking accuracy, an equivalent chassis is transformed based on the stable two-dimensional vehicle dynamic model. Second, a tire blowout–oriented vehicle high-fidelity dynamic model is established based on the equivalent chassis, in which the vehicle lateral, yaw, and roll motions are all considered at the same time. Then, an MPC-based dynamic control strategy is proposed to achieve effective tire blowout suppression with the consideration of vehicle rollover stability. Afterward, a transient vertical tire force shock is employed to simulate the real tire blowout behavior, on which two typical scenarios are constructed based on the TruckSim–Simulink co-simulation platform. The simulation results illustrate the feasibility and effectiveness of the proposed method. In two different dangerous tire blowout conditions, the lateral load transfer rate (LTR) value of the vehicle is reduced by 3.45% and 40.87%, respectively, while the trajectory tracking error is reduced at the same time.

Hierarchical higher-order dynamic mode decomposition for clustering and feature selection

This article introduces a novel, fully data-driven method for forming reduced order models (ROMs) in complex flow databases that consist of a large number of variables. The algorithm utilizes higher order dynamic mode decomposition (HODMD), a modal decomposition method, to identify the main frequencies and associated patterns that govern the flow dynamics. By incorporating various normalization techniques into an iterative process, clusters of variables with similar dynamics are identified, allowing the classification of different instabilities and patterns present in the flow. This method, known as hierarchical HODMD (h-HODMD), has been thoroughly tested in the development of ROMs using three different databases obtained from numerical simulations of a nonpremixed coflow methane flame. The effectiveness of h-HODMD has been demonstrated as it consistently outperforms HODMD in terms of modeling and reconstructing flow dynamics using a reduced number of modes. Additionally, the clusters of variables identified by h-HODMD reveal the algorithm's ability to group chemical species whose behavior is consistent from a kinetic perspective. h-HODMD allows for the construction of inexpensive reduced dynamical models that can predict flame liftoff, identify the occurrence of local extinction and blowout conditions, and facilitate control purposes.

Accretion and obscuration in merger-dominated luminous red quasars

ABSTRACT We present an analysis of the X-ray properties of 10 luminous, dust-reddened quasars from the FIRST-2MASS (F2M) survey based on new and archival Chandra observations. These systems are interpreted to be young, transitional objects predicted by merger-driven models of quasar/galaxy co-evolution. The sources have been well studied from the optical through mid-infrared, have Eddington ratios above 0.1, and possess high-resolution imaging, most of which shows disturbed morphologies indicative of a recent or ongoing merger. When combined with previous X-ray studies of five other F2M red quasars, we find that the sources, especially those hosted by mergers, have moderate-to-high column densities (NH ≃ 1022.5–23.5 cm−2) and Eddington ratios high enough to enable radiation pressure to blow out the obscuring material. We confirm previous findings that red quasars have dust-to-gas ratios that are significantly lower than the value for the Milky Way’s interstellar medium, especially when hosted by a merger. The dust-to-gas ratio for two red quasars that lack evidence for merging morphology is consistent with the Milky Way and they do not meet the radiative feedback conditions for blow-out. These findings support the picture of quasar/galaxy co-evolution in which a merger results in feeding of and feedback from an AGN. We compare the F2M red quasars to other obscured and reddened quasar populations in the literature, finding that, although morphological information is lacking, nearly all such samples meet blow-out conditions and exhibit outflow signatures suggestive of winds and feedback.

Emergency plugging of shear ram failure

Well control (pressure control of the wellbore) plays a crucial role in drilling engineering. As a key equipment in well control, a blowout preventer (BOP) does not only control the wellbore pressure but also serves as the last barrier to well control. Although prevention is the best method to eliminate risks, unexpected failure risks remain in harsh environments, and once the BOP fails, it can result in serious accidents. Therefore, an additional control measure will ensure well control safety. Based on the investigation of the main failure elements and failure forms of the BOP, a simulation model was established in this study for emergency plugging of BOP failure. The reliability of the simulation model was validated through experiments using a high-temperature and high-pressure mud plugging instrument, and the possibility and influencing factors of urgent plugging were analyzed using this model. The results indicated that particles with a particle–pore ratio of 1.6 resulted in the most effective plugging under blowout conditions. The higher the particle concentration, the faster the plugging, and the longer the effective sealing time. Mixing the particles did not improve the plugging effect but can significantly increase the effective plugging time, which is beneficial for subsequent well killing. This study provides an additional means of well control assurance, which can serve as theoretical guidance for ensuring well control safety.

Damage assessment of Baghjan oil field blowout on terrestrial and aquatic ecosystems near Dibru Saikhowa Biosphere Reserve, Assam India

Ecosystems can be severely damaged by oil field blowouts. There is growing need to improve and enhance use of advance scientific tools and techniques for monitoring, mapping, and estimating the impact of oil spills on the terrestrial and aquatic ecosystems. It is also required to estimate the extent of spills to develop effective remediation plans, that ensures improved monitoring systems in place to spot early leakages. The Baghjan oil field blowout in Assam, India, adjacent to the Maguri-Motapung Wetland and the Dibru-Saikhowa National Park, substantially affected the health of nearby terrestrial and aquatic ecosystems. To assess the impact of the oil spill on the vegetation, we used Normalized Difference Vegetation Index and Case2Regional.CoastColour algorithm data to assess the pre and post blowout conditions. Results reflected to 41% increase in senescing vegetation followed by 25% increase in chlorophyll-a, and 35% of the total suspended matter (TSM) during the initial months. During the blowout period total TSM exceeded 175 kg/m3, which was observed to be exceptionally high for the wetland ecosystem. Areas cleared of vegetation after the oil spill were reported to have various levels of re-vegetation in the later year, according to change detection conducted for the two dates. Present study reflects the necessity of using high spatial resolution studies to map precise locations where the oil from the spill entered and later also to evaluate the impact of blowout on the vegetation. Study observed post-blowout changes in plant growth and survival which could be monitored to check ecosystem recovery after a year of oil spill.

E-POD investigations of turbulent premixed flame dynamics approaching lean blow-out conditions

Thanks to the continuous computational power increase, the use of high-fidelity computational fluid dynamics (CFD) simulations is nowadays customary, especially in the gas turbines design process. The extraordinary temporal and spatial detail of such analyses generate large datasets, which must be carefully studied to correlate different quantities and gain information to characterize the behavior of combustor designs. Several advanced post-processing tools have been proposed; however, the Extended-POD (E-POD) holds the greatest potential for turbulent combustion applications when the mutual influence of different quantities is the main goal of the investigation. The present work investigates the application of the E-POD to an LES model of a perfectly-premixed, swirl-stabilized, methane-air flame approaching Lean-Blow-Out. Leveraging the validation against the experimental data at two different operating conditions on a laboratory test case, the numerical model has been used to collect several quantities of interest for shedding light on the flow-flame interaction near the blow-out. The post-processing algorithm has been used to highlight the differences between two conditions approaching the extinction at distinct air-flow velocities. It has been found that, when the burner is operated with a higher velocity, the flame is subjected to a cyclic low-frequency breakdown around the internal recirculation zone, leading to an ingestion of cold products from the external parts of the combustor toward the center. Although other local effects acting on the flame brush have been found in both conditions, they are related mainly to higher order coherent structures with a lower energy content. As a result, their impact onto flame stability is found to be of secondary importance since their limited interaction with flame stabilization. The work shows that E-POD represents a powerful tool for investigating the key features of flame dynamics even at near-blow-out conditions, constituting a valid algorithm for interpreting the results of CFD analyses on gas turbines combustors.

The diagnostics of the effect of flooding of multi-phase oil-gas mixture on the blowout of wells

The paper deals with the study of the degree of flooding effect of well product in the hydraulic characteristics of the multi-phase lift and the development of the diagnostics method of the impact of flooding increase on the well blowout. On the basis of the multi-phase technologies, the bottomhole pressure corresponding to the end of blowout period considering the flooding and flow regimes of well product has been specified. It was defined that the diagnostics of the blowout conditions becomes possible due to the change of pressure gradient by the section of multi-phase lift.

Three-Dimensional Stability Investigation of Trapdoors in Collapse and Blowout Conditions

Three-Dimensional Stability Investigation of Trapdoors in Collapse and Blowout Conditions

Sinkhole Stability in Elliptical Cavity under Collapse and Blowout Conditions

Road subsidence and sinkhole failures due to shallow cavities formed by defective water main have increased in recent decades and become one of the important research topics in geotechnical engineering. The present paper numerically studies the stability and its associated failure mechanism of ellipse-shaped cavity above defective water mains using the finite element limit analysis technique. For a wide range of geometrical parameters, the pressure ratio method is used to formulate the stability solutions in both blowout and collapse scenarios. Even though there is no published solution for elliptical cavities under blowout failure conditions, the obtained numerical results are compared with available circular solutions. Several conclusions are drawn based on the failure mechanism study of the various ellipse shape transformations in this study, whilst design charts and equations proposed for practical uses.

Dynamics of stratified swirl flame near lean blow out

This paper studies the flame dynamics near lean blowout (LBO) conditions in a stratified swirl burner. The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions. In the experiments, only the pilot flame works with four different equivalent ratios. It is found that as the flame changes from stable combustion to near LBO, the flame macrostructure changes from V-shape to M-shape. Meanwhile, a characteristic frequency of 405 Hz is found in the spectrum of heat release signal. The closer to LBO, the higher amplitude is found at the frequency peak. Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame. Large-eddy simulations (LESs) via OpenFOAM reproduce the flame dynamics near LBO, which agrees with the experimental results. LESs provide more insights into the flow fields, showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction. This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO. The heat release signal is also found can be used as a candidate precursor for LBO.

Spray Characteristics of Standard and Alternative Aviation Fuels at Cold-start Conditions

The spray characteristics of standard and alternative aviation fuels created by a hybrid pressure-swirl airblast (HPSA) atomizer were investigated at conditions corresponding to engine cold start for an aviation gas turbine. Drop size and drop velocity of sprays from three different fuels, Jet-A (A-2), JP-5 (A-3), and a JP-5/farnesane blend (C-3) were investigated using a phase Doppler anemometry. The spatially resolved drop measurements were obtained at three axial locations downstream of the swirler exit plane and up to 30 mm in the radial direction from the spray centerline. Smaller , , and were observed when increasing the pressure drop across the atomizer swirler (). Increasing also increased the mean axial velocity. No definitive trend was observed with viscosity on drop size, while liquid–gas surface tension showed a weak correlation with drop size due to its small variation in value among fuels. The spray unsteadiness was examined using interparticle arrival time distribution functions. A semi-empirical model was also developed using a phenomenological three-step model for the atomization process of the HPSA atomizer and was used to predict drop-size values at engine cold-start conditions in this work and near lean blowout conditions presented in earlier work.

On the initiation of blow-out from cooktop burner jets: A simplified energy-based description for the onset of laminar flame extinction in premixed hydrogen-enriched natural gas (HENG) systems

Due to the prohibitive financial expense and logistical difficulties of a wholesale changeover from natural gas to hydrogen, hydrogen-enriched natural gas (HENG) offers a more viable intermediate solution for offsetting the carbon dioxide output of domestic gas usage and reducing the blow-out susceptibility of natural gas flames. In order to formulate a practically useful description of the blow-out threshold, the present work addresses the minimum energy per unit volume of premixed gas required for the sustained combustion of HENG fuels with molar hydrogen concentrations between zero and 50 mol%. By considering a ring burner comprising circular burner jet apertures with diameters in the range 1.0–2.4 mm, this critical energy density was demonstrated to increase linearly with the mean velocity of the admitted gas premixture, approaching a value that was common to all of the investigated HENG compositions in the limit of zero flow. Furthermore, despite flame morphology varying substantially as a function of flow conditions, the visible surface area of critically stable flames consistently exhibited an empirical squared dependence on the power generated by combusting fuel. By combining these correlations, the onset of blow-out was shown to be well-approximated by a formula that relates the critical surface-averaged laminar burning velocity to the mean velocity of gas molecules at the burner jet. This model provides a simplified means of predicting blow-out conditions from measurable input parameters and could serve as an invaluable asset for the design of new HENG burner systems or the retrofitting of existing natural gas appliances.

Effect of different turbulence model on prediction of lean blowout limit for micro gas turbine combustor

ABSTRACT This paper aims to present turbulence modelling results of methane/air combustion in a micro gas turbine combustor. Modelling studies were carried out with different turbulence models to evaluate Lean Blowout (LBO) performance on the micro gas turbine combustion chamber by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are k-epsilon standard, k-epsilon RNG, K-epsilon realisable, k-omega standard, and k-omega SST. A two-dimensional axisymmetric 3 kW swirl stabilised micro gas turbine combustor model was built to investigate the impact of various turbulence models on the prediction of LBO behaviour of the combustor fuelled with methane. Performance evaluation of these models was executed by calculating the average exit gas temperature (AEGT) that have been used for predicting the blowout conditions. Results obtained from this study were validated with experimental results. Numerical results showed that two-equation turbulence models give consistent simulation results with experimental results employing trend and value. Standard k-epsilon was found to give consistent simulation results with experimental data.

Nonreacting Spray Characteristics for Alternative Aviation Fuels at Near-Lean Blowout Conditions

The spray characteristics of standard and alternative aviation fuels generated by a hybrid pressure-swirl airblast atomizer were studied at conditions corresponding to near-lean blowout conditions: ambient gas pressure , fuel temperature , and atomizing gas temperature . The candidate alternative fuels (C-1, C-5, C-7, and, C-8 synthetic blends) were compared to Jet-A (A-2). The drop size and drop velocity were measured using phase Doppler anemometry at three measurement planes downstream of the swirler exit. The representative diameters [, , and the mass mean diameter (MMD)] were used to characterize the drop size. The drop velocity was characterized using the arithmetic mean and the root mean square. An increase in the swirler pressure drop () showed a decrease in the mean drop size and an increase in the magnitude of the axial drop velocity. Comparing the different fuels generally showed an increase in for higher fuel viscosity. However, definitive trends in and the MMD were not observed, based on fuel physical properties such as viscosity, surface tension, or density. A variation of the fuel injection pressure showed no significant effect for both the standard and alternative fuels. The full cone angle (obtained using shadowgraph images) was found to not vary significantly with or .

The impact of swirling flow strength on lean-dome LDI pilot mixers’ operability and emissions

In an effort to reduce the environmental impact of aviation, lean-dome combustion concepts such as lean direct injection (LDI) are being pursued for their potential to achieve very low emissions. However, low-emissions potentials may be accompanied by operability challenges. In the present effort – part of a series of fundamental investigations into LDI operability challenges – systematic experiments of lean-dome-relevant pilot combustor devices are conducted in a single-element methane-fueled combustor test rig with two different LDI configurations by using a suite of optical diagnostics. While maintaining all other design features constant, the clockwise vane angle of the outer air swirler is altered between 60° (LDI-60-CW configuration) and 45° (LDI-45-CW configuration), representing strong and weak swirling flows, respectively. Measurements of the non-reacting/reacting flow fields and flame characteristics are performed as a function of overall equivalence ratio via time-resolved particle image velocimetry, OH*/CH*/NO2* chemiluminescence, OH planar laser-induced fluorescence, and broadband flame imaging. It is found that a large center recirculation zone exists only with the LDI-60-CW configuration, while the LDI-45-CW flow is dominated by a swirling jet flow. In addition, it is shown that the center recirculation zone in the LDI-60-CW configuration results in noticeably lower lean blowout limits than the LDI-45-CW configuration, but at the cost of much higher NOx production for vigorously-burning equivalence ratios. At lower equivalence ratios near lean blowout conditions, both configurations result in similar NOx production. These results are discussed in terms of identifying possible research directions for optimizing LDI designs for reduced NOx emissions while maintaining or improving operability relative to current rich-dome combustion technology.

Planar measurements of CO concentrations in flames at atmospheric and elevated pressure by laser-induced fluorescence

The article describes the development and application of a laser-optical technique for the quantitative measurement of carbon monoxide (CO) in combustion environments of elevated pressures relevant of gas turbine environments. Planar CO measurements can provide important information for the understanding of several aspects of the combustion process, such as localized lean blowout conditions or quenching effects of effusion cooling on the combustor flow. While laser-induced fluorescence is a sensitive non-intrusive measuring technique suitable for planar detection, the CO molecule cannot be excited directly in the visible or near UV. For the present implementation, a two-photon excitation scheme with resulting fluorescence in the visible range is utilized. To qualify the technique, planar measurements in a laminar premixed atmospheric flame are performed in a first step; this flame is later on used for calibration of CO concentrations in a laminar premixed flame at elevated pressure up to 5 bar and in a generic turbulent combustor with a swirl-stabilized flame operated at atmospheric pressure. Pressure effects on spectral structures and the calibration procedure are discussed, as well as potential interference by cross-sensitivity with other species. Based on this optimization strategies are defined for the respective experimental arrangements.

Analysis of transient blow-out dynamics in a swirl-stabilized combustor using large-eddy simulations

In the present work, the flame structure and dynamics of a swirl-stabilized methane/air flame near and at blow-out conditions are investigated using large-eddy simulations (LES). To this end, simulations at stable conditions and during a transient blow-out sequence are performed employing a flamelet/progress variable (FPV) model and a thickened flame (TFLES) approach with finite-rate chemistry. Good agreement is obtained for velocities, OH mass fraction profiles, and statistics between LES and measurements at conditions near blow-out. Lift-off height comparisons reveal that the TFLES model predicts a significantly less stable flame compared with the FPV model, which is consistent with the stability limits observed for the two models. Subsequently, transient blow-out simulations are performed and examined. This analysis is guided by employing early warning indicators from dynamical system analysis to identify critical transition points and precursors that trigger the onset of blow-out. It is found that the variance of the integrated heat release is a sensible quantity as an early warning signal in detecting blow-out. Detailed comparisons are then performed between the two models to examine the difference in terms of the blow-out mechanism. The comparison reveals that the different phases of the transient blow-out sequence are qualitatively similar for the two models. However, local extinction phenomena are more significant for the TFLES model, reducing the stabilizing feedback by hot combustion products and leading to a total blow-off time, which is three times shorter compared to FPV.