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Homogeneous charge combustion in a four stroke cycle spark-ignition engine was studied using through-piston-photography with a gated-intensified CCD camera. Analysis of computer stored multiple exposed flame front images was carried out for various engine conditions, in conjunction with the test data and cylinder pressure signals. Representative turbulence scales were inferred from the flame propagation and cylinder pressure data. Fractal analysis of flame edge contours resulted in a fractal dimension D3 in the range 2.12 to 2.23 corroborating data presented elsewhere. A correlation is presented here between the standard deviation of peak cylinder pressure and the fractal dimension D3.

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.)--West Virginia University, 1998. / Title from document title page. "December 3, 1998." Document formatted into pages; contains xii, 110 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-65).