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Let’s discuss evaporative cooling, the mechanism by which our bodies regulate temperature. When it is too warm, we sweat, and the liquid cools our skin as it evaporates.
A similar phenomenon is used to cool down homes and businesses in many hot, dry areas, like the desert regions of the Southwest. In these systems, water is evaporated from hot air, emitting much cooler, moist air. You’ll also often see this principle utilized by restaurants with outdoor patio seating areas, which spray mists of atomized water to make them more comfortable on hot days. Evaporative cooling is preferable relative to the traditional refrigeration systems required in areas with higher humidity because it is much less energy intensive.
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All liquids have an associated heat of vaporization, which is a measure of the cooling that results from vaporizing a given mass. The table compares the cooling effect of a given mass of water to the cooling effect of gasoline and bioethanol. Water has a very high heat of vaporization, meaning that the vaporization process removes significant heat from the surrounding air. Indeed, this is one reason why both our bodies and evaporative coolers are so good at regulating temperature.
Gasoline has a very low heat of vaporization. In other words, your body would not be able to cool itself very well if you were to sweat gasoline. Bioethanol has about 2.5 times the heat of vaporization of gasoline, but still far less than water. The cooling effect you feel when using hand sanitizer is from the evaporation of bioethanol, the predominant ingredient.
Why does this matter to your engine? Engines rely on fuel vaporization to cool internal components such as valves and pistons. In fact, under prolonged acceleration, engines inject extra fuel for the sole purpose of cooling critical components. The higher heat of vaporization of bioethanol enhances this cooling effect relative to gasoline, thereby providing engine protection and longevity.
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Another benefit of increased heat of vaporization is increased resistance to knock. The high-octane benefits of bioethanol are well understood, but higher octane underrepresents the knock resistance benefits. This is because the Motor Octane Test procedure specifies a fixed intake temperature for the fuel-air blend, where, in reality, the induction temperature of an engine running with bioethanol in the fuel is reduced by the higher heat of vaporization. Knock is perpetrated by heat, so reduced induction temperatures provide a knock resistance benefit not comprehended in the Motor Octane Number (MON).
In short, just as sweat cools our bodies on a hot day, bioethanol cools and protects your engine — naturally enhancing performance, durability, and efficiency in ways traditional gasoline simply can’t match.
