Thermal and Flow Fields Modeling of Fast Spark Discharges in Air

2006 ◽  
Vol 129 (1) ◽  
pp. 55-65 ◽  
Author(s):  
O. Ekici ◽  
O. A. Ezekoye ◽  
M. J. Hall ◽  
R. D. Matthews
Keyword(s):  
Ambient Pressure ◽  
Early Time ◽  
Spark Discharge ◽  
Pressure Effects ◽  
Local Thermal Equilibrium ◽  
Heat Conducting ◽  
Current Profile ◽  
Spark Plug ◽  
Time Flow ◽  
History Of

In this study, a two-dimensional axisymmetric computational model of spark discharge in air is presented to provide a better understanding of the dynamics of the process. Better understanding of the modeling issues in spark discharge processes is an important issue for the automotive spark plug community. In this work we investigate the evolution of the shock front, temperature, pressure, density, geometry, and flow history of a plasma kernel using various assumptions that are typically used in spark discharge simulations. A continuum, inviscid, heat conducting, single fluid description of the flow is considered with radiative losses. Assuming local thermal equilibrium, the energy input due to resistive heating is determined using a specified current profile and temperature-dependent gas electrical conductivity in the gap. The spark discharge model focuses on the early time flow physics, the relative importance of conduction and radiation losses, the influence of thermodynamic model choice and ambient pressure effects.

scholarly journals The history effect in bubble growth and dissolution. Part 1. Theory

2016 ◽  
Vol 800 ◽  
pp. 180-212 ◽  
Author(s):  
Pablo Peñas-López ◽  
Miguel A. Parrales ◽  
Javier Rodríguez-Rodríguez ◽  
Devaraj van der Meer
Keyword(s):  
Bubble Dynamics ◽  
Ambient Pressure ◽  
Time History ◽  
Interfacial Concentration ◽  
Interface Concentration ◽  
Governing Differential Equation ◽  
History Of ◽  
History Effect ◽  
Isothermal Regime

The term ‘history effect’ refers to the contribution of any past mass transfer events between a gas bubble and its liquid surroundings towards the current diffusion-driven growth or dissolution dynamics of that same bubble. The history effect arises from the (non-instantaneous) development of the dissolved gas concentration boundary layer in the liquid in response to changes in the concentration at the bubble interface caused, for instance, by variations of the ambient pressure in time. Essentially, the history effect amounts to the acknowledgement that at any given time the mass flux across the bubble is conditioned by the preceding time history of the concentration at the bubble boundary. Considering the canonical problem of an isolated spherical bubble at rest, we show that the contribution of the history effect in the current interfacial concentration gradient is fully contained within a memory integral of the interface concentration. Retaining this integral term, we formulate a governing differential equation for the bubble dynamics, analogous to the well-known Epstein–Plesset solution. Our equation does not make use of the quasi-static radius approximation. An analytical solution is presented for the case of multiple step-like jumps in pressure. The nature and relevance of the history effect is then assessed through illustrative examples. Finally, we investigate the role of the history effect in rectified diffusion for a bubble that pulsates under harmonic pressure forcing in the non-inertial, isothermal regime.

scholarly journals Use of the mathematical model of the ignition system to analyze the spark discharge, including the destruction of spark plug electrodes

Open Physics ◽  
2018 ◽  
Vol 16 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Sebastian Różowicz
Keyword(s):  
Mathematical Model ◽  
Experimental Studies ◽  
Fuel Mixture ◽  
Spark Discharge ◽  
Fuel Additives ◽  
Ignition System ◽  
Spark Plug ◽  
The Mathematical Model

Abstract The paper presents the results of analytical and experimental studies concerning the influence of different kinds of fuel additives on the quality of the spark discharge for different configurations of the ignition system. The wear of the spark plug electrode and the value of spark discharge were determined for various impurities and configurations of the air-fuel mixture.

Abstract 3173: Imaging Findings at the Earliest Stages of Intracerebral Hemorrhage

Stroke ◽  
2012 ◽  
Vol 43 (suppl_1) ◽  
Author(s):  
Adrian M Burgos ◽  
Nerses Sanossian ◽  
David Liebeskind ◽  
Leonid Groysman ◽  
Pablo Villablanca ◽  
...  
Keyword(s):  
Intracerebral Hemorrhage ◽  
Brain Imaging ◽  
Early Time ◽  
Field Evaluation ◽  
Imaging Findings ◽  
Imaging Studies ◽  
Lentiform Nucleus ◽  
History Of ◽  
The Mean ◽  
Fazekas Scale

Background: Imaging findings in intracerebral hemorrhage (ICH) patients at ultra-early time points have not been well characterized. Objective: To describe imaging findings in consecutive ICH patients being transported by ambulance within 2 hours from symptom onset. Methods: We analyzed consecutive ICH patients enrolled in the multicenter, NIH Field Administration of Stroke Therapy (FAST-MAG) clinical trial. First brain imaging studies obtained in the ED were independently reviewed by 2 neurologists for ICH location, volume, presence of intraventricular hemorrhage (IVH), heterogeneity (defined as >20 point difference in Hounsfield units), irregular borders, multilobulation, and substantial edema (defined as >0.5cm). Leukoaraiosis was graded using the Fazekas scale for periventricular and deep white matter changes (0-3 for each). Results: Among 127 patients (enrolled en route to 23 hospitals), mean age was 66 (SD 14), 34% were women, 35% had Hispanic ethnicity, 83% were white, and 84% had a history of HTN. At time of first field evaluation by paramedics [mean 31 (SD 23) minutes after last known well time (LKWT)], the initial BP was 177/95 (SD 34/22) and median (IQR) Glasgow Coma Scale of 15 (15-15). First brain imaging studies were obtained a mean of 100 (SD 35, range 54-255) minutes after LKWT, and were CT in 90% and MRI in 10%. Location of ICH was most often in the lentiform nucleus (42%) followed by thalamus (40%), and cortex (4%), with one case each of caudate, pons, and cerebellar deep nuclei. The mean volume of initial hematoma was 19.6 (SD 23) ml. IVH was present in 45 (35%), significant edema in 13 (10%), and midline shift in 24 (19%). Hemorrhage density was heterogeneous in 34 (27%), multilobulated in 55 (43%) and with irregular borders in 77 (60%). Leukoaraiosis (LA) was common, with moderate to severe LA (Fazekas grades 2, 3) present in the periventricular region in 58% and deep regions centrum semiovale in 35%. Conclusions: Among ICH patients presenting within the first 2h, deep hemorrhages predominate over superficial and intraventricular extension is already present in one-third, but ICH volume is moderate and substantial edema present in only one-tenth. These findings suggest substantial opportunities for intervention to avert hemorrhage and edema growth ultra-early after ICH onset.

Effect of spark discharge energy scheduling on ignition under quiescent and flow conditions

2020 ◽  
Vol 234 (12) ◽  
pp. 2878-2891
Author(s):  
Zhenyi Yang ◽  
Xiao Yu ◽  
Hua Zhu ◽  
David S-K Ting ◽  
Ming Zheng
Keyword(s):  
Flow Velocity ◽  
High Power ◽  
Cross Flow ◽  
Spark Discharge ◽  
Discharge Process ◽  
Discharge Energy ◽  
Flow Conditions ◽  
Flame Kernel ◽  
Spark Plug ◽  
Spark Energy

The enhancement of the breakdown power during the spark discharge process has been proved to be beneficial for the flame kernel formation process under lean/diluted conditions. Such a strategy is realized by using a conventional transistor coil ignition system with an add-on capacitance in parallel to the spark plug gap in this paper. In practical application, the use of different ceramic material other than aluminum oxide can change the parasitic capacitance of the spark plug, achieving similar effect in terms of rescheduling the discharge energy released during the breakdown phase. Detailed research has been carried out to investigate the effect of the parallel capacitance and the cross flow velocity on the flame kernel formation and propagation process. With the increase in parallel capacitance, more spark energy is delivered during the breakdown phase, while less energy is released during the arc/glow phase. Shadowgraph images of the spark plasma reveal that the high-power spark discharge can generate a larger high-temperature area with enhanced electrically prompted turbulence under quiescent conditions, as compared with that using the conventional transistor coil ignition discharge strategy under the same condition. The breakdown enhanced turbulence of the high-power spark is proved to be beneficial for the flame kernel development, especially with the lean or exhaust gas recirculation diluted combustible mixtures, given that sufficient spark energy is available for the high-power spark strategy to successfully generate the breakdown event. The results of combustion tests under flow conditions reveal that the breakdown enhanced turbulence of the high-power spark tends to be overshadowed by the turbulence generated from the flow field, and both the increase in flow velocity and parallel capacitance contribute to the reduction in discharge duration of the arc/glow phase. Therefore, the benefits brought about by the high-power spark discharge tend to diminish with the intensification of flow velocity.

Measurement of vibrational and rotational temperature in spark-discharge plasma by optical emission spectroscopy: Change in thermal equilibrium characteristics of plasma under air flow

2018 ◽  
Vol 20 (7) ◽  
pp. 746-757 ◽  
Author(s):  
Masao Kinoshita ◽  
Takayuki Fuyuto ◽  
Hiroshi Akatsuka
Keyword(s):  
Thermal Equilibrium ◽  
Optical Emission Spectroscopy ◽  
Discharge Plasma ◽  
Vibrational Temperature ◽  
Rotational Temperature ◽  
Air Flow ◽  
Optical Emission ◽  
Spark Discharge ◽  
Spark Plug ◽  
Spark Discharge Plasma

The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy, and the influence of the air flow velocity and ambient pressure on these temperatures was investigated. The optical emissions from the plasma were led to an imaging spectroscope through an optical fiber. The temperature was estimated by fitting a theoretically calculated spectrum to that which had been acquired experimentally, formed by nitrogen molecule emission from 372 to 382 nm. The spark-discharge plasma was examined with a flow of ambient air at a discharge energy of 80 mJ. The air flow caused the spark-discharge channel to elongate downstream. At the center of the spark plug gap, the vibrational temperature in the plasma was 4000 K, whereas the rotational temperature was 2000 K. This plasma can be regarded as being in non-thermal equilibrium because the vibrational temperature was higher than the rotational temperature. At a position approximately 3 mm downstream from the spark plug gap, the vibrational and rotational temperatures increased to 4500 and 4000 K, respectively, while approaching each other. Both temperatures reached a maximum value. These results show that the plasma transitions from non-thermal equilibrium to thermal equilibrium as it is elongated by the air flow. Ignition efficiency improvements can be expected if the time required to transition from non-thermal to thermal equilibrium can be shortened.

scholarly journals Identification of Immunologic and Pathologic Parameters of Death versus Survival in Respiratory Tularemia

2007 ◽  
Vol 76 (2) ◽  
pp. 486-496 ◽  
Author(s):  
Damiana Chiavolini ◽  
Joseph Alroy ◽  
Carol A. King ◽  
Peter Jorth ◽  
Susan Weir ◽  
...  
Keyword(s):  
Systemic Disease ◽  
Early Time ◽  
Severe Pneumonia ◽  
Immunoglobulin M ◽  
Immune Markers ◽  
Inflammatory Protein ◽  
Chemotactic Protein ◽  
History Of ◽  
Future Evaluation ◽  
Disseminated Disease

ABSTRACT Francisella tularensis can cause severe disseminated disease after respiratory infection. The identification of factors involved in mortality or recovery following induction of tularemia in the mouse will improve our understanding of the natural history of this disease and facilitate future evaluation of vaccine candidate preparations. BALB/c mice were infected intranasally with the live vaccine strain (LVS) of F. tularensis subsp. holarctica and euthanized at different stages of disease to analyze the induction of immune molecules, gross anatomical features of organs, bacterial burdens, and progression of the histopathological changes in lung and spleen. Tissue-specific interleukin-6 (IL-6), macrophage inflammatory protein 2, and monocyte chemotactic protein 1 were immune markers of mortality, while anti-LVS immunoglobulin M and IL-1β were associated with survival. Moribund mice had enlarged spleens and lungs, while surviving mice had even more prominent splenomegaly and normal-appearing lungs. Histopathology of the spleens of severely ill mice was characterized by disrupted lymphoid follicles and fragmented nuclei, while the spleens of survivors appeared healthy but with increased numbers of megakaryocytes and erythrocytes. Histopathology of the lungs of severely ill mice indicated severe pneumonia. Lungs of survivors at early time points showed increased inflammation, while at late times they appeared healthy with peribronchial lymphoid aggregates. Our results suggest that host immune factors are able to affect bacterial dissemination after respiratory tularemia, provide new insights regarding the pathological characteristics of pulmonary tularemia leading to systemic disease, and potentially identify immune markers associated with recovery from the disease.

Case Study of Ambient Pressure Effects on Pore Shape in Solid

2017 ◽  
Vol 31 (4) ◽  
pp. 796-804 ◽  
Author(s):  
Shih-Yen Hsiao ◽  
Peng-Sheng Wei
Keyword(s):  
Ambient Pressure ◽  
Pressure Effects ◽  
Pore Shape

scholarly journals Drama in Ho Chi Minh City literature and art life

2015 ◽  
Vol 18 (4) ◽  
pp. 47-60
Author(s):  
Thuy Trung Luu
Keyword(s):  
20Th Century ◽  
21St Century ◽  
Performance Art ◽  
Early Time ◽  
High Time ◽  
Ho Chi Minh City ◽  
Late 20Th Century ◽  
Early 21St Century ◽  
The Future ◽  
History Of

In the history of Vietnamese drama, Saigon was one of the places absorbing Western drama from the early time. Although drama in Saigon-Ho Chi Minh City didn’t develop in a smooth and straight way, it was a continuous and unbroken process. This process brought in strong development of drama in Ho Chi Minh city in two decades of the late 20th century and the early 21st century. However, in recent years, drama in Ho Chi Minh City seems to proceed slowly, which reflects some irrational aspects from drama script, performance art to performance operation. Therefore, it’s high time to review the whole history of drama in Saigon-Ho Chi Minh City to collect experiences for the steady development of drama in this City in the future.

scholarly journals The First fm/c of Heavy-Ion Collisions

2019 ◽  
Vol 69 (1) ◽  
pp. 447-476 ◽  
Author(s):  
S. Schlichting ◽  
D. Teaney
Keyword(s):  
Heavy Ion Collisions ◽  
Early Time ◽  
Heavy Ion ◽  
Gluon Plasma ◽  
High Energy ◽  
Nonequilibrium Dynamics ◽  
Local Thermal Equilibrium ◽  
Time Dynamics ◽  
Ion Collisions ◽  
The Many

We present an introductory review of the early-time dynamics of high-energy heavy-ion collisions and the kinetics of high-temperature quantum chromodynamic matter. The equilibration mechanisms in the quark–gluon plasma uniquely reflect the nonabelian and ultrarelativistic character of the many-body system. Starting with a brief exposé of the key theoretical and experimental questions, we provide an overview of the theoretical tools employed in weak coupling studies of the early-time nonequilibrium dynamics. We highlight theoretical progress in understanding different thermalization mechanisms in weakly coupled nonabelian plasmas, and discuss their relevance in describing the approach to local thermal equilibrium during the first fm/ c of a heavy-ion collision. We also briefly discuss some important connections to the phenomenology of heavy-ion collisions.

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