Browsing by Author "Priede, T"

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    The effect of inlet swirl on knock limits in spark ignition engines
    (1992) Allison, Colin Bidden; Priede, T
    An investigation was undertaken to determine the effect of swirl ratio on knock limits in spark ignition engines. Initially it was attempted to find a correlation between swirl ratio and Knock Limited Spark Advance (KLSA) for a selection of commercially available engines. A comparison of measured swirl ratios and KLSA indicated that no such correlation could be found. This was put down to the fact that other factors such as combustion chamber shape and spark plug location play a more dominant role in affecting knock limits than swirl level. Following from this, a single engine with a relatively poor swirl ratio was selected and the swirl level was altered. A novel method of increasing and decreasing the swirl level, with the same pressure drop in each case was developed, and this development is described. This method made it possible to perform dynamometer tests, measuring the KLSA timing for the cases of low and high swirl, while keeping all other parameters such as pressure, temperature, spark plug location and combustion chamber shape constant. All these factors are known to have an effect on the occurrence of knock. In this manner it was possible to determine whether swirl alone has any effect on knock limits. It was found that the high swirl case exhibited higher values of knock limited spark advance above the low swirl case although there was no significant change in torque. A comparison of rubber castings of the inlet ports of numerous engines was made, and is presented in a photographic form. This was done in order to assess how inlet port geometry affects swirl ratios. It was found that a helically shaped inlet port produced the greatest swirl ratio, non directed ports have average values and multiple inlet valve ports have very low swirl ratios. Furthermore, a comparison of swirl ratios of an inlet port with and without deposits, demonstrates that deposits have a significant effect on swirl ratios and volumetric efficiency. However, although the volumetric efficiency was reduced, the deposits enhanced the swirl ratios for this particular case. This is contrary to the general belief that deposits reduce swirl.
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    Heat losses in internal combustion engines
    (1989) Clarke, Ralph Henry; Priede, T
    This thesis deals with the effects of cooling and heat losses in internal combustion engines. The object of this work was to examine and research various cooling concepts and methods to reduce heat loss to engine coolant, improve thermal efficiency and to predict heat transfer values for these alternatives. The optimum system to be considered for possible application to small rural stationary engines. A literature survey was undertaken, covering work performed in the field of internal combustion engine cooling. Besides the conventional cooling system, two concepts emerged for consideration. These were the precision cooling system and the new heat pipe concept, the latter being relatively unknown for internal combustion cooling application. The precision cooling system, consists of a series of small bore tubes conducting coolant only to the critical areas of an engine. The theory being that in the conventional systems many regions are overcooled, resulting in excessive heat loss. The heat pipe is a device of very high thermal conductance and normally consists of a sealed tube containing a small quantity of fluid. Under operating conditions the tubular container becomes an evaporator region in the heat input area and a condenser region in the heat-out area. It is therefore basically a thermal flux transformer,attached to the object to be cooled. The heat pipe performance is also capable of being modulated by varying its system pressure. This is a positive feature for internal combustion engine application in controlling detonation and NOx emissions. Various facts were obtained from the literature survey and considered in the theoretical review. These facts were extended into models, predicting the heat transfer performance of each concept in terms of coolant heat outflow and heat transfer coefficients. The experimental apparatus was based on an automotive cylinder head with heated oil passing through the combustion chamber and exhaust port to simulate combustion gases. Experiments were conducted on this apparatus to validate the predicted theoretical performance of the three concepts. Tests were also made to observe the effect of heat pipe modulation and nucleate boiling in the precision system. Concept theory was validated as shown by the experimental and test results. The performance for each system approximated the predicted heat transfer and heat loss values. By comparison of the heat input, coolant heat outflow values and heat transfer coefficients it was found that the precision system was the most efficient, followed by the heat pipe and the conventional system being the least efficient. It was concluded that the heat loss tests provided a valuable insight into the heat transfer phenomenon as applied to the three systems investigated. This work also illustrated the effects of the variation of coolant flow, velocity and influence of nucleate boiling. This thesis has shown the potential of the systems tested, for controlling heat losses in internal combustion engines. The research work has created a data base for further in-depth evaluation and development of the heat pipe and the precision cooling system. Based on the findings of the experimental work done on this project, several commercial applications exist for the heat pipe and precision cooling systems. Further in-depth research is recommended to extend their potential in the automotive industry.
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    The octane requirement of spark ignition engines
    (1991) Bleimschein, G E; Priede, T; Dutkiewicz, Ryszard Karol
    The thesis covers the fundamentals of refining and fuel technology, engine technology as regards parameters which influence knock and the results of engine tests. Definitions of octane number and the interpretation of the system developed to establish these numbers using the CFR engine are given. The literature survey covers the fundamental refining processes which are used to upgrade gasoline components in order to raise their octane quality or to achieve a more suitable distillation range. Some of the reactions which take place are described and operating conditions for the reactions to occur are given. The chemistry of fuels which affects their octane quality is given and discussed. Generally, aromatics have very good octane values but straight chain paraffins are poor in this regard.