Abstract
Cooling systems in internal combustion engines can be based on liquid, air, or a combination of both. This study presents two cases of cooling system failure in a four-stroke internal combustion engine cooled by a combination air and liquid cooling system with ethylene glycol as coolant. The coolant elastomer hoses in these engines are made of PET-reinforced silicone rubber braid. The decline in mechanical performance of such elastomer hoses following exposure to extreme temperature and certain liquids is a known phenomenon. In this study, the effect of environmental conditions on hose tensile strength was examined using fractography, and analytical and mechanical tests under various ambient conditions and different combinations of oil, air, and coolant. Engine temperature was tracked in several locations in the engine. The signs of hose failure were exhibited as changes in color, swelling, fiber separation, or disintegration. Engine temperature measurements showed that the failure occurred in highest temperature location. It also indicated that the high temperature is a result of the proximity to the exhaust manifold which is located directly below the coolant hose. This study demonstrates for the first time that the exposure to a high temperature and to ethylene glycol as a combination is a critical factor in compromising the mechanical properties of PET-reinforced silicone rubber. Moreover, it is destructive than exposure to either high temperature or ethylene glycol separately. In fact, this study shows that combined exposure to ethylene glycol and a high aging temperature (200 °C) caused a decrease of a 79% in tensile strength and a 61% decrease was noticed as a result of exposure to high temperature and air. Designers of engine cooling systems and similar applications can utilize the results of this study when deciding on cooling system location, type of thermal insulation, coolant liquid, and hoses material.
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