An estimation of the performance of spark ignition methanol engines

Bibliography: pages 54-61.The possibility of using methanol as an alternative fuel for petrol and diesel engines has been investigated at the University of Cape Town in recent years by the Energy Research Institute. Engines, taken from existing road vehicles, were converted to methanol operation and evaluated. During the planning phase of each conversion, it was apparent that there was a need for a method of estimating the probable performance of the converted engine. The objective of this thesis was therefore to develop a generally applicable formula for predicting the rated performance of a methanol-fuelled, spark-ignition engine given only the bore, stroke, number of cylinders and maximum rated engine speed. The prediction was based on an estimate of the indicated efficiency, the volumetric efficiency and the frictional losses of a methanol engine, from which the shaft power and overall efficiency could be determined. The performance of three engines, which were converted to methanol operation, was used to test the theory. The conversions were each of a very different nature: - a) An automotive petrol engine of which only the carburettor was modified. b) An automotive petrol engine that was modified to take advantage of the properties of methanol to improve the performance. c) A truck diesel engine that was converted to spark ignition for operation on methanol. The predicted results were found to compare favourably with the experimental results, with the exception of one spurious reading. An analysis of the range of error in the theoretical estimate was used as the basis for comparison: Range of error in predicted overall efficiency ± 6%. Range of error in predicted shaft power ± 10%. The work of this thesis would be applicable in situations where a quick answer was required and few details were available. With the aid of a programmable calculator, the anticipated performance map could be obtained in a few minutes