Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 438-443).

Thesis (Ph. D.)--University of Michigan, 1915. / "Reprinted from the Physical review, n. s., vol. X, no. 2, August, 1917."

The increase in breakdown potential of a spark channel, formed by discharging a high current pulse between tungsten electrodes, has been studied at times after the current pulse ceases. The dependence of the breakdown potential on time is called the recovery characteristic of the spark channel. The characteristics have been measured for spark channels in air, hydrogen, nitrogen, argon and sulfur hexafluoride. Two new methods of measuring the spark channel temperature and diameter are described. In the first, the temperature is determined from the breakdown potential of an auxiliary spark gap in the second, the temperature is deduced by measuring the velocity of sound in the channel with piezo-electric pressure probes. The results indicate that the maximum diameter of the channel is determined by the interaction between the channel and gas in the surrounding vessel. Temperature measurements agree with the results of earlier workers. By using layered electrodes with tungsten surfaces, it is shown that the recovery characteristic of air sparks is controlled by the cooling effects of the electrodes. Measurements on hydrogen sparks, demonstrate that the breakdown potential increases significantly 10 ¯¹ sees after the spark channel is formed. Changes produced by doping the hydrogen with water vapour and oxygen indicate that this delayed increase in breakdown potential is produced by the adsorption of hydrogen onto the tungsten electrode surfaces. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 59.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xxiii, 284 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 227-235).

Pressure data measurements have been made in a single-cylinder, spark-ignition engine over 100 consecutive cycles. The engine was operated on natural gas at a wide range of engine speed and equivalence ratios. The effects of spark electrode geometry, combustion chamber geometry, spark gap and throttling have also been examined. From these pressure measurements standard deviations in burning times in mass-fraction-burned values were determined. Because of the existing evidence that the origin of cyclic variations is in the early combustion period, the standard deviations of cyclic variation in time required for a small (almost zero) mass-fraction-burned is estimated by extrapolation. These extrapolated values of standard deviation are compared with the implication of a hypothesis that cyclic variations in combustion in spark-ignition engines originate in the small-scale structure of turbulence (after ignition). The nature of turbulence structure during combustion is deduced from existing knowledge of mixture motion within the combustion chamber of the engine. This research determines the turbulent parameters, such as turbulence intensity, turbulent length scales and laminar burning velocity. The standard deviation in burning times in the early stages of combustion is estimated, within experimental uncertainty, by the parameter ⋋/4uℓ where ⋋ is the Taylor microscale and uℓ is the laminar burning velocity of the unburned mixture. This parameter is the consequence of the Tennekes model of small-scale structure of turbulence and Chomiak's explanation of the high flame propagation rate in regions of concentrated vorticity and the assumption that theignition behaves as though it were from a point source. The general conclusion reached is that the standard deviation in the burning time for small mass-fraction-burned is associated with the early stages of burning-predictable from the knowledge of the Taylor microscale and the laminar burning velocity. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

No description available.

Lean burn in spark-ignition engines offers a significant efficiency advantage compared with stoichiometric operation. The lean operation is restricted by increasing cyclic fluctuation in torque. In order to make use of the efficiency advantage and meet the mandatory emission standards the lean operation limit has to be further extended. This requires particular control of the mixing of fuel and air. To study the effect of mixture formation on cyclic variability and to provide quantitative information on the mixing of air and fuel planar laser-induced fluorescence (PLIF) was developed and applied to an operating SI engine. The method is based on imaging the fluorescence of a fluorescent marker (3-pentanone) mixed with the fuel (iso-octane). 3-pentanone was found to have similar vaporisation characteristics to those of iso-octane as well as low absorption and suitable spectral properties. The technique was applied to an one-cylinder SI engine with a cylinder head configuration based on the Honda VTEC-E lean burn system. The mixture formation process during the inlet and compression stroke could be described by measuring the average fuel concentration in four planes, between 0.7 and 15.2 mm below the spark plug, in a section of the cylinder orthogonal to the cylinder axis. The results showed that for 4-valve pent-roof cylinder head systems with swirl inlet flows, fuel impinging on the cylinder wall opposite to the inlet valves has a major influence on the mixture formation process. In order to quantify the cyclic variability in the mixture formation process and its contribution to cyclic variability in combustion the fuel concentration in a plane near the spark plug was measured on a large number of cycles. It could be shown, that the fuel concentration in a small region close to the spark plug has a dominating effect on the subsequent pressure development for lean mixtures. Variations in the mixture concentration in the vicinity of the spark plug contribute significantly to cyclic variations in combustion. In order to address the issue of no uniformity in residual gas concentration prior to ignition a laser induced fluorescence method was developed to measure nitric oxide (NO) concentrations in the unburned charge in the same one-cylinder research engine. Measurements of average and instantaneous NO concentrations revealed, that the residual gas is not homogeneously mixed with the air and that significant cyclic variations in the local residual gas concentration exist.

Texte remanié de: Dissertation--Erlangen-Nürnberg--Friedrich-Alexander-Universität, 2002. / Bibliogr. p. 261-274.

Thesis (Ph. D.)--University of Illinois. / "Scholastic record." Reprinted from the Physical review, vol. XXXI, no. 3, September, 1910.