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Thesis (Ph. D.)--University of Wisconsin--Madison, 1957. / Typescript. Abstracted in Dissertation abstracts, v. 17 (1957) no. 10, p. 2238-2239. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [135]-[136]).

A Thesis submitted to the faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy / Thermodynamic analysis techniques for the study of combustion in compression ignition engines were developed and refined. The techniques were validated against test runs of diesel fuelling, and were then applied to the almost unexplored case of combustion of aspirated dimethyl either (DME) acting as ignition promotor and supplementary fuel, and injected methanol as main fuel. Combustion chamber pressure versus crank angle data were captured for single engine cycle on normal fuelling (methanol and DME), fuelling with DME alone and pure motoring (no fuel) all at essentially identical engine conditions. These data were analysed by a number of mutually complementary techniques. / AC2017

South Africa produces alternative fuels from a number of different sources. The properties of a fuel are known to affect the nature of combustion in compression-ignition engines significantly, and have occasionally resulted in engine failures. Combustion analyses have been conducted on a wide range of fuels and combustion has been thoroughly quantified. However, the role played by the different combustion variables in failures was not known. The result was that it was not possible to predict the implications of variations in the nature of combustion. There was thus a need to investigate the relative role of combustion variables in the failure of engines. The mechanisms of combustion and engine failure were studied. All the variables required to determine combustion and engine durability were measured simultaneously. This research required the development of a complete engine research facility as well as specialized transducers. Fast response surface thermocouples were designed and constructed in order to monitor transient surface temperatures. Heat transfer rates were then calculated with the aid of Fourier analysis. Dynamic stresses were monitored by strain-gauges applied to the engine. A special high speed data acquisition system was developed. An existing heat release model was modified and used to calculate combustion rates. A comprehensive finite element model was developed to calculate piston temperatures and stresses. The role of each combustion variable in stress and durability was investigated by statistical analysis. The results successfully identified the causes of combustion related engine failures. The primary cause of engine failure was found to be thermal loading. The principal cause of any variation in thermal loading and thus engine durability was maximum cylinder pressure. The life of the engine was proved to be determined almost entirely by peak cylinder pressure. The role of the rate of pressure rise was proved to be insignificant. All the implications of variations in the nature of combustion can now be determined accurately. It will thus be possible to optimise engine modifications and fuel properties before validation by durability testing. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.

Investigations into the combustion of alternative fuels in compression-ignition engines in South Africa have underlined the inadequacies of existing zero-dimensional combustion models. The major aspect of concern in these models was the computation of heat transfer which had been singled out by a number of researchers as the leading cause of inaccuracies in heat release computations. The main objective of this research was to develop a combustion model that was less empirically based than the existing zerodimensional models for use in evaluating the combustion and resulting thermal stresses generated by alternative fuels. in diesel engines. Particular attention was paid to the development of a spatial and temporal model of convective heat transfer that was based on gas flow characteristics and to the introduction of a radiation heat transfer model that made use of fuel properties and fuel-air ratio. The combustion process was divided into two zones representing burnt and unburnt constituents and the resulting temperatures in each zone were used in the calculations of convective and radiative heat transfer. The complete model was formulated in such a way that it could be applied with the aid of a micro-computer. Calibration and verification of the gas flow sub-models which involved the squish, swirl and turbulence components necessitated the use of published data. Good agreement for the squish and swirl components was obtained between the present model and the experimental data from three engines, two with a bowl-in-piston and the other with a flat piston. These gas flow components dominated the gas velocities in the combustion chamber and provided a reliable foundation for the calculation of convective heat transfer. In spite of the well documented difficulties of characterising turbulence, after calibration the model generated turbulence levels with acceptable trends and magnitudes. Tests were carried out on a naturally aspirated ADE 236 engine involving the measurement of cylinder pressure and heat flux at a single point. Motored engine data were used to verify the convective heat transfer rates and to ascertain the effects of soot deposition on the heat flux probe. Close correlation between predicted and measured heat flux was achieved after accounting for the effects of chamber geometry at the probe site. Soot deposition on the probe caused a significant attenuation of the heat flux within a short period of the engine running under fired conditions. The results from fired engine tests showed that the two zone combustion model was providing plausible trends in the burnt and unburnt zone temperatures and that the model generated combined heat transfer rates which were credible not only on a global basis but also in terms of point predictions in the combustion chamber. The results also highlighted the considerable variation in heat transfer that could occur from one point in the chamber to another. Such variations added considerable weight to the objective of moving away from a zero-dimensional model to a quasi-dimensional type where predictions could be made on a more localised rather than global basis. It was concluded that the model was a definite improvement over zero-dimensional models and competed favourably with existing quasi-dimensional models with advantages in both simplicity and accuracy. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.

A basic study on the convective flame-wall heat transfer in diesel engines was performed with a fundamental experiment and simplified theoretical models. Based on the concept of flame tubes, a combustor was designed and optimized to support laminar, stable flame propagation at constant ambient pressure. Measurements of flame position and heat transfer during head-on quenching of premixed methane-air flames with varying mixture equivalence ratios at a metallic surface were made using flame luminosity videography and surface thermometry. Two models were developed to predict the magnitude of single-wall quenching layers and the flame-wall heat transfer at a variable temperature wall. One of the models was a quasi steady-state first law balance which utilizes an Arrhenius reaction equation to represent the temperature sensitivity of the chemical processes according to a single-step reaction mechanism. The second model was based on transient heat conduction theory; a planar, moving heat generating sheet simulated the heat release of a propagating flame front in a one-dimensional slab of gases at rest, bounded at the wall at which quenching occurs. Experimental and model results showed that flame-wall heat transfer is primarily dictated by the reaction rate of combustion and the thermal diffusivity of the gas mixture. The convective heat transfer coefficient was predicted to increase with rising wall temperature. Measured peak heat transfer rates were 25% higher than those reported in the literature. Recommendations are made for the design of an experimental apparatus with which conditions encountered in internal combustion engines can be simulated more closely. / Master of Science