Bunsen Burner Flame Research Articles

Experimental and kinetic modeling study on laminar flame speeds and emission characteristics of oxy-ammonia premixed flames

The low flame speed and NOx emissions of ammonia are the key to affecting combustion temperature, stability, flame structure, and pollutant control, limiting its application in power generation devices. This study proposes oxy-ammonia combustion (oxygen content in oxidant = 100%, NH3/O2 combustion) as a novel method for significantly enhancing ammonia combustion. A method for measuring the laminar flame speed using the NH* distribution of the Bunsen burner flame is proposed, and the measured data is close to the constant volume combustion bomb. 21 kinetic models were collected and optimized after comparison with the experimental data of constant volume combustion bombs, and results show that Han et al.'s model has higher prediction accuracy for NH3/O2 flames. The preheating temperature was relevant to gas turbine combustors (298.15–500 K), and the equivalence ratio ranged from 0.7 to 1.6. At this extreme condition (oxygen content in oxidant = 100%), the results show that the maximum laminar flame speed reaches 1.25 m/s at ambient pressure and temperature, which is approximately 18 times that of NH3/air combustion, mainly due to the increased reaction rates of OH, H, O and NH2 radicals in the reaction zone (primary ammonia decomposition and H/O radical pool). The NO emission of NH3/O2 combustion at stoichiometric conditions is about 7216 ppmv@15%O2, 1.5 and 13 times that of NH3/air and CH4/air combustion, respectively. NO production and consumption may follow the N2O and NNH mechanism, and HNO is an important precursor for NO formation. Increasing the preheating temperature has less effect on the reaction pathway directions in the reaction network of nitrogen conversion but affects the path flux significantly.

Optimized CT-TDLAS reconstruction performance evaluation of least squares with the polynomial-fitting method

Computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS) has been widely used in the diagnosis of the combustion flow field. Several optimized CT reconstruction algorithms such as iteration methods, transformation methods, and nonlinear least squares were applied. Considering the industrial application background, the performances of algebraic iteration reconstruction with the simultaneous algebra reconstruction technique (SART), Tikhonov regularization, and least squares with the polynomial fitting method were discussed in this study. For the mentioned algorithm, identical simulated reconstruction parameters that contained 32-path laser structures, assumed temperature distribution, and absorption databases were adopted to evaluate the reconstruction performance including accuracy, efficiency, and measurement of environment applicability. In this study, different CT reconstruction algorithms were also used to calculate the temperature distribution of the Bunsen burner flame. The different reconstruction results were compared with thermocouple detection data. With the theoretically simulated and experimental analysis, the least squares with the polynomial fitting technique has advantages in reconstruction accuracy, calculation efficiency, and laser path applicability for the measurement condition. It will be helpful in enhancing CT-TDLAS technique development.

De Giorgi type results for equations with nonlocal lower-order terms

It is known that the De Giorgi’s conjecture does not hold in two dimensions for semilinear elliptic equations with a nonzero drift, in general, $$\begin{aligned} \Delta u+ q\cdot \nabla u+f(u)=0 \ \ \text {in } \ \ {\mathbb {R}}^2, \end{aligned}$$when \(q=(0,-c)\) for \(c\ne 0\). This equation arises in the modeling of Bunsen burner flames. Bunsen flames are usually made of two flames: a diffusion flame and a premixed flame. In this article, we prove De Giorgi type results, and stability conjecture, for the following local-nonlocal counterpart of the above equation (with a nonlocal premixed flame) in two dimensions, $$\begin{aligned} \Delta u + c L[u] + f(u)=0 \quad \text {in} \ \ {{\mathbb {R}}}^n, \end{aligned}$$when L is a nonlocal operator, \(f\in C^1({\mathbb {R}})\) and \(c\in {\mathbb {R}}^+\). In addition, we provide a priori estimates for the above equation, when \(n\ge 1\), with various jumping kernels. The operator \(\Delta +cL\) is an infinitesimal generator of jump-diffusion processes in the context of probability theory.

Modelling of turbulent hydrogen-blended premixed flames using algebraic flame surface wrinkling closure for the Lewis numbers and mean local burning velocity

Hydrogen-blended fuel is of fundamental interest due to difficulties in modelling and its practical significance for the development of high-performance hydrogen combustion devices and safety technologies for the prediction and prevention of fire or explosion. In this analytical study, we validate an algebraic premixed turbulent model [13] for molecular transport effects in both spherical expanding methane flames enriched with hydrogen and Bunsen burner flames. Experiment comparisons are supported with theoretical ideas. Bunsen flames are measured at varied turbulence, equivalence ratios, temperatures, and pressures. We also consider other, very recent, experimental data [32] of similar fuel mixtures to support the trends.In the study of outwardly evolving spherical expanding flames, we present three variants of this model, with two functions based on the Lewis number Le, and one based on the experimentally measured mean local flame burning velocity SFm. The Lewis number is significant in understanding the role of the diffusion of deficient reactants, which is particularly noticeable in blended fuels. The utilitarian part of this work is to demonstrate that the Le-based premixed turbulent models take into account the preferential diffusion effect, and to embed a term that quantifies turbulent flame speed explicitly for mixtures, for example, having the same unstretched burning velocity as the model input. We show that in the modelling of turbulent burning velocity, the use of SFm avoids the use of input parameters the unstretched laminar flame speed and the Lewis number. Moreover, we validate high-pressure experiments by Bagdanavicius [12] to show that the pressure has less significant impact on the Bunsen flames and, therefore, we model without the pressure term. The model correlates well with most of the data.

Отсутствие зажигания стенки из жесткого пенополиуретана от искры дуговой электросварки

Ствие случаев зажигания пенополиуретана, которое объясняется малым временем контакта искры с поверхностью пенополиуретана t. Приводятся экспериментальные оценки фактического значения t и минимально необходимого для зажигания пенополиуретана времени контакта с искрой t. It is known that sparks of electric arc welding, representing drops of molten metal (hereinafter - iron sparks), have a high incendiary ability. However, due to a number of reasons, there is possible a situation when electric welding does not lead to the ignition of nearby combustible materials. The identification of such causes can have an important impact on the development of a standard method for investigating the ignition power of sparks. The work investigated the possibility of spark ignition of a vertical layer of rigid polyurethane foam installed on a laboratory table (hereinafter referred to as walls). The wall was exposed to sparks from electric arc welding with a power of up to 6 kW. The distance from the source of sparking to the wall was (15 ± 3) 10 m. A separate experiment lasted several minutes until the electrode burned out, the diameter of which varied from 2 mm to 4 mm. Research results and their discussion. In none of the experiments was it possible to ignite the wall with sparks. Sparks bounced off the surface of the polyurethane foam and fell down onto the horizontal surface of the laboratory table. To explain the results, an experimental estimate was made of the time t of the interaction of the drop with polyurethane foam and the minimum time t of such interaction, leading to the ignition of the wall. The estimate t < 30 · 10 s is based on frames of video recording with a frequency of 30 s of a luminous trail of a spark, curved by a collision with a wall. The estimate t > 1 s is based on simulated droplet exposure with small scale Bunsen burner flames of varying duration. Therefore, t << t. The reason for the lack of ignition of polyurethane foam was the short contact time of the electric arc welding spark with the surface of the polyurethane foam.

Ignition and burning of the composite sample impacted by the Bunsen burner flame: A fully coupled simulation

Experimental study and three-dimensional simulation of warming up, ignition, and subsequent burning out of the composite material impacted by the attached Bunsen burner flame is presented. The specimen is the fiberglass-reinforced composite with the epoxy resin binder. In the experiment, vertical specimen was located above the laminar diffusion flame, and transient variation of specimen mass and surface temperatures was recorded until the matrix polymer burned out. In the simulations, thermal decomposition of the composite was evaluated by the in-house pyrolysis model Pyropolis coupled with the general-purpose CFD solver, which simulated the flames generated by the burner and by the combustible volatiles. Formal kinetics of thermal decomposition of matrix polymer and the heat of combustion of volatiles have been derived from the microscale combustion calorimetry measurements. The simulation results include favorable comparisons of experimental and predicted dynamics of material degradation and flame behavior. Transient spatial distributions of surface temperature, burning rate, and heat fluxes (net, radiative and convective) are demonstrated. This study is the step towards developing the computational framework capable of replicating and predicting the outcome of standard fire tests UL94 and VBB.

Characteristics of a Single Sensor Fiber-Coupled Three-Dimensional Particle Image Velocimetry for Reacting Flow-Fields

Abstract Tomographic particle image velocimetry (Tomo-PIV) has become a standard tool for capturing a three-dimensional (3D) velocity fields in nonreacting flows. However, the diagnostic approach can become costly and challenging to implement when extended to applications which require high-speed cameras. This limitation has led to the use of fiber wound bundles to allow for multiple views to be captured on a single camera sensor. Additionally, employing this diagnostic approach on reacting flow-fields becomes more complex as the introduction of the flame causes additional luminosity and optical distortion which impacts the particle field reconstruction. This work seeks to validate and determine the limitations when utilizing a single sensor fiber-coupled approach for capturing Tomo-PIV data on a reacting flow-field. A premixed propane (C3H8) and air Bunsen burner flame is utilized to examine if the single sensor approach can meet the parameters for acceptable reconstruction based on previous research. The resulting velocity fields are then compared to a traditional PIV measurement to assess the deviation of the single sensor approach from a standard velocimetry measurement approach. It is demonstrated that there is strong agreement between the velocity and vorticity for the average flow-fields; however, when comparing the Reynolds shear stresses, a significant deviation is revealed. The deviation is attributed to strong velocity fluctuations occurring within the instantaneous Tomo-PIV data, which creates a significant divergence between the measurement techniques on an instantaneous basis. This demonstrates that while the approach can obtain reliable velocity and vorticity statistics, there are significant limitations in calculating second-order turbulence statistics. Thus, revealing that there is a tradeoff between the ability to extract the full velocity gradient tensor and the extent of the turbulence-related analysis which can be reliably performed.

Hexachlorocyclotriphosphazene Functionalized Graphene Oxide as a Highly Efficient Flame Retardant.

A flame-retardant composite was synthesized through a simple graphene oxide functionalization route with hexachlorocyclotriphosphazene and p-phenylenediamine. Flame experiments conducted on the synthesized composite proved its importance as tremendously resistant to fire. The thermogravimetric analysis (TGA) shows clearly that the functionalized graphene oxide (FGO) exhibits an enhanced thermal stability and better temperature resistance. A thermoset epoxy resin was prepared by incorporating different percentages (2, 5, and 10%) of FGO to diglycidyl ether of bisphenol A (DGEBA). The flame-retardant properties, thermal degradation behavior, and combustion of the DGEBA thermosets cured by m-phenylenediamine were investigated using a Bunsen burner flame approaching the flame temperature of a fire and TGA. The chemical structure of FGO was characterized with spectroscopic and imaging techniques including Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, TGA, scanning electron microscopy, energy-dispersive X-ray spectroscopy elemental mapping, and X-ray photoelectron spectroscopy. Due to its high flame-retardant capabilities, such a composite could promise potential applications in the manufacture of inflammable materials for different uses.

Structure and Laminar Flame Speed of an Ammonia/Methane/Air Premixed Flame under Varying Pressure and Equivalence Ratio.

This paper presents a joint experimental and numerical study on premixed laminar ammonia/methane/air flames, aiming to characterize the flame structures and NO formation and determine the laminar flame speed under different pressure, equivalence ratio, and ammonia fraction in the fuel. The experiments were carried out in a lab-scale pressurized vessel with a Bunsen burner installed with a concentric co-flow of air. Measurements of NH and NO distributions in the flames were made using planar laser-induced fluorescence. A novel method was presented for determination of the laminar flame speed from Bunsen-burner flame measurements, which takes into account the non-uniform flow in the unburned mixture and local flame stretch. NH profiles were chosen as flame front markers. Direct numerical simulation of the flames and one-dimensional chemical kinetic modeling were performed to enhance the understanding of flame structures and evaluate three chemical kinetic mechanisms recently reported in the literature. The stoichiometric and fuel-rich flames exhibit a dual-flame structure, with an inner premixed flame and an outer diffusion flame. The two flames interact, which affects the NO emissions. The impact of the diffusion flame on the laminar flame speed of the inner premixed flame is however minor. At elevated pressures or higher ammonia/methane ratios, the emission of NO is suppressed as a result of the reduced radical mass fraction and promoted NO reduction reactions. It is found that the laminar flame speed measured in the present experiments can be captured by the investigated mechanisms, but quantitative predictions of the NO distribution require further model development.

An FPGA-Based On-Chip Neural Network for TDLAS Tomography in Dynamic Flames

A back propagation (BP) neural network is introduced and implemented on a field programmable gate array (FPGA) chip into tunable diode laser absorption spectroscopy (TDLAS) tomography for fast response and a high signal-to-noise ratio (SNR) in temperature and water concentration imaging. The network implemented on the FPGA extracts the peak values of normalized second harmonics of absorption spectra. A recursive demodulator based on a Kalman filter generates outputs of the training database. Compared with the typical quadrature demodulator, the sampling time of the BP neural network drops to one-quarter of the typical one, with a 5 dB increase in the SNR at different noise levels. To verify and evaluate the proposed method, the FPGA-based 32-bit fixed-point BP neural network was compared with the floating-point BP neural network and the quadrature demodulator in numerical simulations. In the real experiments, Bunsen burner flames with acoustic excitation were imaged, and noisy distortions of the normalized second harmonics and average temperature were effectively reduced by using the proposed method. Temporal fluctuations of up to 750 Hz can be clearly identified from variations of reconstructed distributions of temperature and water vapor molar concentration, in which cases the typical quadrature demodulator failed to work. These results showed that the proposed method works well in the FPGA chip and reveals more details in dynamic flame monitoring.

Graphene-based intumescent flame retardant on cotton fabric

We have developed functionalized graphene oxide (FGO) nanocomposites-based intumescent flame-retardant coating. The graphene surface was functionalized by potassium carbonate by reacting graphene oxide (GO) and potassium carbonate (K2CO3). The resultant coating improved the flame retardancy of the cotton fabric. The FGO nanocomposite-coated fabric was to prove the flame retardancy properties of the FGO nanocomposite, by detail flame tests such as limiting oxygen index, vertical flammability test and exposure to the Bunsen burner flame (~ 1500 °C) test. FGO-coated material, when exposed to fire, was observed to maintain its original shape with the release of little smoke initially and later developed char-like material. Prepared materials were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The cotton fabric alone burnt in 5 s, but when coated with the FGO, it was able to withstand the fire for more than 325 s (5.25 min), whereas the only GO- and K2CO3-coated fabrics were completely burned out within 10 s and 20 s, respectively. This obtained FGO nanocomposite coating is proved to be an efficient flame retardant with an easy, simple one-pot and inexpensive technique in comparison with the reported works. In this work, we have synthesized functionalized graphene nanocomposites, which act as an efficient flame retardant. The recent process established that this is a simple and eco-friendly method for efficient graphene-functionalized IFR.

Analysis of the Closures of Sub-grid Scale Variance of Reaction Progress Variable for Turbulent Bunsen Burner Flames at Different Pressure Levels

The statistical behaviour and modelling of the sub-grid variance of reaction progress variable have been analysed based on a priori analysis of direct numerical simulation (DNS) data of turbulent premixed Bunsen burner flames at different pressure levels. An algebraic expression for sub-grid variance, which can be derived based on a presumed bi-modal sub-grid distribution of reaction progress variable with impulses at unburned reactants and fully burned products, has been found to be inadequate for the purpose of prediction of sub-grid variance even for the flames in the wrinkled flamelets/corrugated flamelets regime. Moreover, an algebraic model, which is often used for modelling sub-grid variance of passive scalars, has been found to significantly overpredict the sub-grid variance of reaction progress variable for all the cases considered here. The modelling of the unclosed terms of the sub-grid variance transport equation has been analysed in detail. Suitable model expressions have been identified for the sub-grid flux of variance, reaction rate contribution and scalar dissipation rate based on a priori analysis of DNS data. It has been found that the alternation of pressure does not have any significant impact on the closures of sub-grid flux of variance but a model parameter for the Favre-filtered scalar dissipation rate needs to be modified to account for the variation of pressure.

Mechanism Reduction and Bunsen Burner Flame Verification of Methane

Based on directed relation graph with error propagation methods, 39 species and 231 reactions skeletal mechanism were obtained from Mech_56.54 (113 species and 710 reactions) mechanism of methane. The ignition delay times, laminar flame propagation speed, and important species were calculated using the simplified mechanism at different pressures and equivalence ratios. The simulation results were in good agreement with that of detailed mechanisms and experimental data. The numerical simulation of the Bunsen burner jet flame was carried out using the simplified methane mechanism, and the simulation results well reproduced the temperature, flow fields and distribution of important species at flame zone. The compact methane reduced mechanism can not only correctly respond to its dynamic characteristics, but also can be well used for numerical simulation, which is of great significance in engineering applications.

Dual-Modality Electrical Tomography for Flame Monitoring

Electrical capacitance tomography has been widely used in flame monitoring. In this paper, a dual-modality electrical tomography system was developed for imaging of flame admittivity distribution, including conductivity and permittivity distributions. An admittance measuring circuit was developed to obtain both resistance and capacitance of the flame impedance, and a Calderon method-based reconstruction algorithm was developed, which could be used to directly reconstruct the cross-sectional images of both conductivity and permittivity in the flame. The 2-D and 3-D phantoms were modeled in simulation to validate the feasibility of the developed system and algorithm. Experiments were carried out to monitor a Bunsen burner flame with varied air flow rates. Both simulation and experimental results were confirmed that the developed technique has not only reconstructed the cross-sectional distribution of admittivity in the flame but also revealed variations in flame admittivity with height. In addition, it was discovered that the conductivity and permittivity distributions in the flame were affected by the air flow rates. Therefore, the system can be used to monitor the conductivity and permittivity distributions in the flame and, hence, can further help study the combustion mechanism.

On the validity of Damköhler's first hypothesis in turbulent Bunsen burner flames: A computational analysis

The validity of Damköhler's first hypothesis, which relates the turbulent flame speed to turbulent flame surface area under the condition where the integral length scale of turbulence is greater than the flame thickness, has been assessed using three-dimensional Direct Numerical Simulations (DNS) of turbulent premixed Bunsen burner flames over a range of values of Reynolds number, pressure and turbulence intensity. It has been found for the Bunsen configuration that the proportionality between volume-integrated burning rate and the overall flame surface area is not strictly maintained according to Damköhler's first hypothesis. The discrepancy is found to originate physically from the local stretch rate dependence of displacement speed, and this helps to explain differences observed previously between flames with and without mean curvature. Approximating the local density-weighted flame propagation speed with the unstrained laminar burning velocity is shown to be inaccurate, and can have a significant influence on the prediction of the overall burning rate for flames with non-zero mean curvature. Using a two-dimensional projection of the actual scalar gradient for flame area evaluation is shown to exacerbate the loss of proportionality between volume-integrated burning rate and the overall flame surface area. The current analysis identifies the conditions under which Damköhler's hypothesis remains valid and the necessary correction for non-zero mean flame curvature. Further, it has been demonstrated that surface-weighted stretch effects on displacement speed need to be accounted for in order to ensure the validity of Damköhler's hypothesis under all circumstances. Finally, it has been found that the volume-integrated density-weighted scalar dissipation rate remains proportional to the overall burning rate for all flames considered here irrespective of the value of Reynolds number, pressure and turbulence intensity. However, this proportionality is lost when the scalar dissipation rate is evaluated using the two-dimensional projection of the actual scalar gradient.

A direct numerical simulation analysis of pressure variation in turbulent premixed Bunsen burner flames-Part 1: Scalar gradient and strain rate statistics

Three-dimensional simple chemistry Direct numerical simulations (DNS) of Bunsen burner flames have been carried out for different pressure values. A number of cases have been considered for the same set of values of mean and root-mean-square inlet velocities normalised by the laminar burning velocity and the integral length scale normalised by the nozzle diameter. The modifications of laminar burning velocity and flame thickness with pressure lead to an increase in both flow and turbulent Reynolds numbers with increasing pressure. This also gives rise to changes in Damköhler number and Karlovitz numbers for these flames and thus they occupy different locations on the regime diagram. For this reason, two additional cases at the lowest pressure have been simulated to match the turbulent Reynolds number of the highest-pressure case by changing the normalised root-mean-square velocity in one case, whereas the integral length scale is modified in the other case. It has been found that pressure and turbulent Reynolds number variations do not have significant influences on the mean behaviours of the magnitude of the reaction progress gradient (i.e. Surface Density Function) and fluid-dynamic normal strain rate. However, the length scale separation between the nozzle diameter and flame thickness increases with increasing pressure, which makes the occurrence of the Darrieus–Landau (DL) instability highly likely for the flames at elevated pressures. The presence of the DL instability affects the flame curvature statistics, which in turn influence the mean behaviours of the dilatation rate and fluid-dynamic tangential strain rate.

A Direct Numerical Simulation analysis of pressure variation in turbulent premixed Bunsen burner flames-part 2: Surface Density Function transport statistics

The effects of pressure variation on the transport statistics of the magnitude of the reaction progress gradient (i.e. Surface Density Function (SDF)) have been investigated based on three-dimensional simple chemistry Direct Numerical Simulations (DNS) of Bunsen burner flames representing the flamelet regime of combustion. The large length scale separation between the nozzle diameter and flame thickness for high pressure flames makes the Darrieus–Landau (DL) instability highly likely, which in turn affects the curvature stretch. It has been found that the effective normal strain rate remains insensitive to the pressure variation for the parameter range considered here, which makes the flamelet thickness in turbulent flames comparable to the laminar flame thickness. The influences of the DL instability on the positive mean tangential strain rate counter the effects of instability on the negative mean curvature stretch and thus the effective tangential strain rate (or net flame stretch rate) remains mostly unaffected by the pressure variation within the strict flamelet regime (i.e. wrinkled flamelets and corrugated flamelets regimes) of combustion. The similarities in the SDF and the effective strain rate statistics for different values of pressure suggest that the models for the Flame Surface Density and Scalar Dissipation Rate, which were originally proposed and validated for atmospheric combustion, might remain valid also for elevated pressures.

Dual-resolution Raman spectroscopy for measurements of temperature and twelve species in hydrocarbon–air flames

This paper introduces dual-resolution Raman spectroscopy as a novel diagnostics approach for measurements of temperature and species in flames where multiple hydrocarbons are present. Simultaneous measurement of multiple hydrocarbons is challenging because their vibrational Raman spectra in the C–H stretch region are closely overlapped and are not well known over the range of temperature encountered in flames. Overlap between the hydrocarbon spectra is mitigated by adding a second spectrometer, with a higher dispersion grating, to collect the Raman spectra in the C–H stretch region. A dual-resolution Raman spectroscopy instrument has been developed and optimized for measurements of major species (N2, O2, H2O, CO2, CO, H2, DME) and major combustion intermediates (CH4, CH2O, C2H2, C2H4 and C2H6) in DME–air flames. The temperature dependences of the hydrocarbon Raman spectra over fixed spectral regions have been determined through a series of measurements in laminar Bunsen-burner flames, and have been used to extend a library of previously acquired Raman spectra up to flame temperature. The paper presents the first Raman measurements of up to twelve species in hydrocarbon flames, and the first quantitative Raman measurements of formaldehyde in flames. The accuracy and precision of the instrument are determined from measurements in laminar flames and the applicability of the instrument to turbulent DME–air flames is discussed.

For the love of ferns.

I attended Hampshire College to major in music. While watering plants in the greenhouse to fulfill my community service requirement, I fell in love with a fern. ¶ Intending to make thousands of them, I discovered the college laboratory, where I tweezed the furry rhizomes of Davallia fejeensis into agar-filled test tubes, careful to keep my sleeve out of the Bunsen burner flame used to keep things sterile. Between frat parties and piano practice, I made a discovery: Agar prepared for growing bacteria caused the rhizomes to reprogram and become reproductive-like structures. My discovery set me on a path to research. I would stay on that path for about a dozen years. No one in my family had ever studied science. I was already midway through college, with just a high school biology class behind me. I struggled through remedial math, then chemistry and physics. One graduate school accepted me. For the next 2 years, I taught and worked in a research lab, studying membranes. I aced my graduate courses. Membranes didn't seem to play a role in reprogramming development, so I transferred to Albert Einstein College of Medicine, to a laboratory that studied enzymes involved in transcription and DNA replication. ![Figure][1] “I still love ferns, but I'll let someone else figure out their genetic switches.” ILLUSTRATION: ROBERT NEUBECKER “Be here as often as possible,” my new graduate adviser said. I went to dinner at 5 p.m. and returned at 7 p.m. “Where were you?” he demanded. From then on, I humbly apprenticed myself. I brought dinner in, studied while my gels ran, and slept on the orange vinyl couch in the women's lounge. “You've studied enough. Let's go to a movie,” one boyfriend said. I shooed him away. Another offered marriage and travel if I would quit my Ph.D. program. Ha! My experiments were my life. Finally, I married a cute medical student I met at a mixer in the research center lobby. He followed me to my postdoc at the University of California, Berkeley, where I was a Damon Runyon Cancer Research Foundation Fellow. While my husband was on call, and even when he wasn't, I buried myself in transcription factors that control developmental genes. I applied for tenure-track positions and was offered several: Duke. Johns Hopkins. Brandeis. My husband said he would go anywhere. I committed to Hopkins and wrote my first big National Institutes of Health grant. My husband served me with divorce papers. I fell into a state of shock. Twelve years had passed since I'd fallen in love with my fern. At Hopkins, I was unable to lift a pipette, let alone concentrate on building a lab. I had written for scientific journals, but now I wrote madly in my own journal, using words as therapy to figure out what had gone wrong. An old boyfriend invited me to sunny Los Angeles. Skeptically, I boarded a plane to a world of palm trees, movies, restaurants, and—surprisingly—laughter and love. These were tastes of a life I had missed. For months, I assumed my attraction to this “real” world was a transient response to the trauma of divorce. I expected my love for the lab to return. My grant was rejected by a couple of points. I moved to LA with no job prospects. I became a live-in girlfriend. I remarried, re-divorced, practiced piano again, and raised two children. I bought a house near mountains and hiking trails. I read. I briefly accepted a tenure-track assistant professorship at a liberal arts college, assuming I was ready for the lab again. I wasn't. It was as a teacher that I made sense of myself. Teaching gave me a life of work but also a life of people and play. Colleges, though, want research. I resigned. Today I teach 11th and 12th grade physiology. I have been a school board chair and a high school principal. I often work with special education and at-risk students. Many of them have trouble focusing because of traumatic life events. I can relate. I still love ferns, but I'll let someone else figure out their genetic switches. I'm okay with watering the ferns in my backyard. [1]: pending:yes

Interaction of shock tube exhaust flow with a non-pre-mixed flame

Much of the discussion in the public domain relating to shockwave interaction with flames, and the use of high explosives to extinguish, for instance, oil and gas well fires, is anecdotal and outside of scientific literature. The result is a lack of consistent insight into the physical mechanisms involved. It has been proposed by several researchers that the shock waves and the strong vortex rings from detonations are effective in extinguishing large­scale fires (Akhmetov et al. 1980, 2001, 2009; Bliznetsov et al. 2001). To date, methodical laboratory shock tube work in controlled conditions for simple flame cases has not been reported. Therefore, a preliminary laboratory­scale study was devised to investigate, qualitatively, the interaction between the flow exhausting from an open­ended shock tube and a standard Bunsen burner flame. The shock tube was a basic, compressed air­driven device not capable of producing exactly the kind of temporal pressure profile associated with explosive events (i.e. a Friedlander­esque waveform) (Chandra et al. 2012). However, the flow fields obtained resulted in many interactions not previously observed and documented. This was possible due to the complex flow features emanating from the tube exit, including strongly rotating vortices and a central jet of flow following the initial shock wave (Jiang et al. 2003; Kashimura et al. 2000; Onodera et al. 1998). The flow from the shock tube was expected to be in the low­supersonic range within the immediate vicinity of the exit, with the leading shock and jet both dissipating significantly downstream with an accompanying reduction in planarity. Therefore, the effect of the exhaust flow on the Bunsen safety (yellow) non­pre­mixed flame was examined at 50 mm and 500 mm from the tube exit to investigate the range of interactions possible with this setup. Multiple stagnation pressures in the driver section (from 140 to 620 kPa) were used to examine the influence of Mach number at the exit (1.1–1.4). The shock tube had a 44 mm 9 47 mm rectangular cross­sectional exit, a 1,790 mm long driver section, and a 2,195 mm driven section. The visualization was captured at 6,000–10,000 fps using a Photron APX­RS, with an exposure time of 20 ls. A conventional z­type schlieren arrangement was utilized with a vertical knife­edge cutoff.