Spark gap | EPFL Graph Search

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound (ranging from a snap for a spark plug to thunder for a lightning discharge), light, and heat. Spark gaps were used historically in early electrical equipment, such as spark gap radio transmitters, electrostati

Analytical Methods for the Study and Design of Integrated Switched Oscillators and Antennas for Mesoband Radiation

Jose Felix Vega Stavro

This thesis was carried out within the framework of a scientific cooperation project entitled “Application of High Power Electromagnetics to Human Safety” developed by the EPFL, the National University of Colombia and Los Andes University, Colombia. The project was funded by the Swiss Agency for Development and Cooperation (SDC) through the EPFL Centre Coopéation & Développement (CODEV). The Scientific Cooperation aimed at the study and development of techniques for the generation of high power electromagnetic signals for the disruption or preemptive activation of Improvised Explosive Devices (IEDs) during humanitarian clearance activities. The results and conclusions of the thesis will be applied to the construction of a resonant radiator, which can be used for securing humanitarian demining operations in Colombia. The thesis is devoted to the analysis of a specific type of resonant radiators known as Switched Oscillators (SWO). An SWO is a radiator constituted by a high voltage charging circuit that drives a quarter-wave transmission line resonator connected to an antenna. An SWO can produce high-amplitude, short duration, electromagnetic fields, with a moderate bandwidth, when compared to the main resonance frequency. The outcome of the thesis can be also be used in electromagnetic compatibility applications, for the production of resonant, high power electromagnetic fields, with the aim of testing the immunity of electronic systems against Intentional Electromagnetic Interference (IEMI) attacks. The thesis is divided in three parts. The first part deals with the electrostatic design of an SWO. A method for producing an optimized design of the electrodes forming the spark gap of the SWO is presented. The method is based on the generation of a curvilinear coordinate space on which the electrodes are conformal to one of the coordinate axis of the space. Laplace equation is solved in the interelectrodic space, obtaining an analytical solution for the electrostatic distribution. Furthermore, using appropriate mathematical manipulations, we derive an analytical expression for the impedance of the transmission line formed by the proposed electrodes. The second part of the thesis is devoted to the analysis of SWOs in the frequency domain. An original analysis approach, based on the chain-parameter technique, is proposed in which the SWO and the connected antenna are described using a two-port network using which a transfer function between the input voltage and the radiated field is established. A closed form expression of the resonance frequency of the SWO is also obtained. The developed technique makes it possible to study the response of an SWO when connected to an arbitrary antenna with a frequency-dependent input impedance. The final part of the thesis presents the construction and test of an SWO prototype. The prototype design is based on the theoretical developments presented in the first two parts of the thesis. The realized SWO is experimentally characterized using different antennas. It is characterized by an input voltage of 30 kV and a resonance frequency of 433 MHz. Radiated electric fields using monopole antennas were in the order of 10 kV/m at a distance of 1.5 m. The prototype is used for testing the validity of the electrodynamic model for the analysis of SWOs connected to frequency dependent antennas. Different monopole antennas connected to the SWO are considered and the radiated fields are measured and compared with theoretical calculations. It is shown that the developed theoretical model is able to reproduce with a good accuracy the behavior of the SWO connected to a frequency dependent antenna.

EPFL2013

SWISS MOTOR. Modification d’un moteur diesel pour le fonctionnement au gaz naturel en cogénération. Partie 1: fonctionnement avec mélange stoechiométrique (l = 1).

Daniel Favrat, Roger Röthlisberger

In the frame of the decentralised electrical power and heat cogeneration with stationary I. C. engines operating on natural gas, the Swiss limit for exhaust gas emissions, with 80 mg/mN3 (5% O2), is the most severe in force on an international level. On the other hand, the only technology able to meet this requirement, with the use of a stoechiometric mixture and a three way catalyst, allows a relatively low global engine efficiency and is characterised by a limited reliability of the exhaust gas treatment system. In this context, the Laboratory of Industrial Energy Systems of the EPFL has undertaken, on the basis of a converted diesel engine for natural gas operation, to develop new technologies (mixture, ignition, ...) and to evaluate their potential to reduce exhaust gas emission, particilarly NOx, and reliability. The objective of the first part of this project is to study the behaviour of a naturally aspirated version of the engine “Liebherr G926”, fuelled with a stoechiometric mixture. The main engine characteristics and perfomances have been used to reduce noxious emissions. The main results obtained are: A variation of the spark timing at wide open throttle has allowed to determine the best operating condition with a mixture of l=1.001. The maximal mechanical power output of 106.3 ± 0.5 kW at 1502 ± 5 rpm and the maximal global efficiency of 35.9 + 1,7/-0.6% have been achieved at a spark timing of 20 °CA BTDC. The lowest cycle to cycle variability, with a coefficitent of variability of the mean effective pressure smaller than 1.5%, is reached at the same spark timing (Figure 5.11). No occurrence of knock has been noticed on the spark timing range between 5 and 30 °CA BTDC. An increase of the spark gap from 0.2 up to 1.2 mm reduced the combustion cycle by cycle variability (Figure 5.21) without modifying the engine performances and emissions (Figures 5.15 and 5.17), at full as well as at half load. A increase, respectively a decrease of two units of the spark thermal index from a basis value of 5 has no significant influence on engine performances and emission (Figures 5.23 to 5.26). Similarly, an increase of the central electrode length from 1 up to 3 mm has no detectable effect on the engine behaviour (Figures 5.23 5o 5.26). The use of a three way catalyst for the exhaust gas treatment allows to reduce the NOx and CO emissions well under the Swiss limits (Figure 5.35).

1996

Investigation of Ethylene and Propylene Production from CO2 Reduction over Copper Nanocubes in an MEA-Type Electrolyzer

Raffaella Buonsanti, Valery Okatenko

Previous work carried out in fully liquid environ-ments and at low current densities has demonstrated that highly uniform faceted copper nanocrystals display different selectivity profiles in CO2 reduction compared to polycrystalline copper. As part of ongoing upscaling efforts, it is a matter of interest to investigate whether the high selectivity toward ethylene of copper nanocubes, which show a preferential (100) orientation, is maintained in gas-fed electrolyzers, thus enabling the energy-efficient production of this valuable commodity chemical at industrially relevant current densities. In this work, we assessed the electrochemical CO2 reduction reaction performance of highly uniform copper nanocubes loaded onto gas diffusion electrodes (GDEs) in a zero-gap device. The copper nanocube-loaded GDEs maintained high Faradaic efficiencies toward ethylene at elevated total current densities, resulting in higher overall partial current densities toward this product compared to benchmark electrodes. Interestingly, CO2 reduction to propylene, albeit with low partial current densities, was also observed. However, double-layer capacitance measurements revealed that the performance observed at high current densities is significantly influenced by electrode flooding. The findings of this study can inform future efforts geared toward optimizing the electrodes with this promising class of catalysts.