Results of simulation and experimental testing of a method of forming a periodic temperature pro file on the surface of a dielectric body are presented. The temperature profile is formed by a system of passive electromagnetic (EM) oscillators heated in the field of a quasi optical beam of external microwave radiation. It is shown that, in a system of parallel linear high Q oscillators of a resonance length, a multimode EM field structure is formed, which hampers formation of a uniform periodic structure of energy release zones and, therefore, formation of a regular temperature profile on the model's surface. Feasible ways of solving this problem are proposed, including application of linear EM oscillators situated near a conducting reflecting screen at a distance much shorter than a quarter wavelength of the radiation.
The development of efficient and reliable systems for the ignition of air/fuel mixtures is of interest for many practical applications associated with the use of combustion devices. To increase the total surface of the flame, ensure the reliability of ignition, increase the rate of combustion in the volume of the chamber and the completeness of combustion of the combustible mixture, multi-point ignition of the air/fuel mixture using several pulsed spark discharges is used. A comparison of the characteristics of combustion products in the working chamber when using different numbers of igniting spark discharges is made based on the data of a physical experiment. Measurements are carried out at various ignition points of the mixture, initial mixture pressures, and air/fuel ratios. The values of the air/fuel ratio used in the experiment are in the range, the boundaries of which are the lower and upper concentration limits of the ignition of the propane-air mixture.
The induced field of a cylindrical electromagnetic vibrator with spherically rounded ends is cal culated. The vibrator is above a flat screen placed in a linearly polarized quasi optical microwave beam. The plane of the screen is perpendicular to the Poynting vector of the radiation. The axis of the vibrator is aligned with the vector of the exciting field electrical component. In calculation, the length of the vibrator and the vibrator-screen distance were varied, while its diameter and the initial field were kept constant. It is found that the induced field of the vibrator with a length close to the half wavelength of the field is maximal at the ends of the vibrator and the field strength resonantly depends on the length of the vibrator. The shortening of the "half wavelength" vibrator that provides a maximal induced field is determined. The result of numerical simulation is to an extent intriguing. It is revealed that the induced field of a resonance half wavelength vibra tor rises considerably when the vibrator-screen distance becomes shorter than the quarter wavelength of the field. The Q factor of an equivalent electromagnetic oscillating circuit characterizing the vibrator also grows, and the induced field more and more concentrates between the screen and the surface of the vibrator's ends facing the screen. Full scale experiments qualitatively support theoretical predictions. The results allow researchers to considerably extend the application area of vibrators as initiators of breakdown in high pres sure gases to ignite microwave discharges in quasi optical beams with a low initial field.
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