In this dissertation, some practical ignition techniques are presented that show how some problems of lean-burn combustion can be overcome. Then, to shed light on the effects of the ignition techniques described, the focus shifts to the more specific problem of the early phase of spark ignition. Thermal models of ignition are reviewed. These models treat the energy provided by the electrical discharge as a point source, delivered infinitely fast and creating a spherically symmetric ignition kernel. The thesis challenges the basis of these thermal models by reviewing the work of many investigators who have clearly shown that the temporal characteristics of the discharge have a profound effect upon ignition. Photographic evidence of the early phase of ignition, as well as other evidence from the literature, is also presented. The evidence clearly demonstrates that the morphology of spark kernels in the early phase of development is toroidal, not spherical as suggested by thermal models. A new perspective for ignition, a fluid dynamic point of view, is described. The common ignition devices are then classified according to fluid dynamics. A model describing the behaviour of spark kernels is presented, which extends a previously established mixing model for plasma jets, to the realm of conventional axial discharges. Comparison of the model behaviour to some limited data is made. The model is modified by including the effect of heat addition from combustion, and ignition criteria are discussed. / Graduate

An attempt has been undertaken to enhance turbulence in an S.I. engine at the final stage of the compression stroke, without affecting the intake process. The method employed to control the turbulence level made use of an original design called the squish-jet combustion chamber. The design had potential to generate jets in the chamber before CTDC and thus create dramatically different turbulent flow patterns. Natural gas, a slow burning fuel, was used for performance tests, and different levels of turbulence were expected to markedly affect the combustion process. A flow visualization experiment was performed under conditions similar to a motored engine. As a result, the jet development in the squish-jet type combustion chamber was documented. A new type of a flat cylinder head, and a set of squish-jet pistons were designed and manufactured. Experiments conducted on the redesigned Ricardo Hydra, single cylinder research engine, evaluated the influence of the squish-jet chamber on the mixture motion and the engine performance over a wide range of operating conditions. The jet velocities were measured with a hot wire probe located in the piston bowl, and turbulence parameters with a probe inserted through a cylinder head. The squish-jet design was evaluated for 6 different configurations. As a result it has been established that the squish-jet design does not create jets strong enough to dramatically enhance the turbulent flow field. The design, however, diminished the squish effect which is shown to be very important for the middle part of flame development. The simple squish design produces faster burning rate in the first half of the combustion process and develops the highest peak pressures. Variabilities of both cyclic IMEP and peak pressure are found to be unaffected by the presence or absence of strong squish motion. This suggests that the most important phase of combustion for the cyclic variation is the initial stage of the flame development. A comparison of ensembled pressure signals between combustion chamber designs, conducted at RAFR=1.00 and at RAFR=1.25 shows less dispersion in the latter case. It appears that at lean operation mixture motion influences combustion process to a lesser degree than at stochiometric conditions. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Thesis (M.S.)--Michigan State University. Dept. of Mechanical Engineering, 2008. / Title from PDF t.p. (viewed on July 27, 2009) Includes bibliographical references (p. 119-122). Also issued in print.

Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 28, 2008) Includes bibliographical references (p. 170-176).

Thesis (MEngSc)--University of Melbourne, Dept. of Mechanical and Manufacturing Engineering, 2009. / Typescript. Includes bibliographical references (leaves 140-149)

Thesis (Ph.D.)--University of Melbourne, Dept. of Mechanical Engineering, 2009. / Typescript. Includes bibliographical references (leaves 231-245)

No description available.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 29, 2007) Includes bibliographical references (p. 153-155).