Effect of coolant temperature on performance of a SI engine

Abstract

This research work is aimed at investigating the effect of variation of coolant temperatures ranging from 45-85°C, thus effecting the heat removal rate, on the performance of an automotive 81 engine. The specific aim of this study was to investigate the effect of variation of cooling water temperature as well as the cooling rate on the P-t and P-V diagrams of the engine cycle, at different speed and load conditions. A pressure transducer connected to the combustion chamber, signal conditioning hardware and a high-speed data acquisition device is used for recording cyclic variation of pressure. A position sensor tracks the TDC location as a time series, from which the cylinder volume is calculated using piston-cylinder dimensions. Performance parameters such ~s brake specific fuel consumption rate, air-fuel ratio, temperatures of coolant, lubricating oil as well as the engine body and emission analysis of the exhaust gases were also investigated at different engine speed and load conditions. Investigations revealed that increased coolant temperature reduced the heat losses and resulted in slight improvement of specific fuel consumption. No significant change on the pressure-volume relationship was noticed. Variation of coolant temperature in this range did not change the combustion inside the cylinder very much, resulting in insignificant changes in exhaust temperature and emission analysis. The detrimental effects observed was the elevation of temperature of the engine parts and the lubricating oil. Although multi-grade lubricating oils appeared to be coping up with the rise of temperatures resulting in steady engine operation. Elevated body temperatures may have detrimental effect on the operational life of various non-metallic and metallic engine parts. When the , coolant temperature was raised above 85°c the heat transfer and temperature rise became unstable due to local boiling and formation of vapour locks, leading to rapid engine overheating. This investigation may have practical implications when many automotive engines in Bangladesh are run with faulty/inadequate cooling systems 'specially in congested traffic jams in hot summer days.