L09 - Chapter 9: Automobiles Motivation. Car engine cycle...

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Chapter 9: Automobiles – Motivation. Car engine cycle • Amongst the applications of technology, automobiles have a substantial impact both upon the society and environment • Cars function based on conversion of chemical energy of the fuel into mechanical energy by engines with internal combustion • In these engines, a mixture of gasoline and air is burned inside the cylinder containing the piston in a succession of processes: 9.1,2 intake compression expansion (power stroke) exhaustion Gas in Fuel ignition Gas out
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Automobile Emissions – Octane rating. Emissions • The quality of the gasoline used by the engine is one of the factors influencing the efficiency of the engine, as well as the amount of the pollutants in the exhaust gas • The gasoline quality is typically described using the octane rating a ranking based on the type of alkane hydrocarbons in the chemical composition • Alkanes have composition C n H 2n+2 , and give the best efficiency for n = 8 (isooctane) and worst when n = 7 (heptane). Accordingly, isooctane is assigned an octane rating of 100 and heptane of 0. • Mixture of alkanes can be characterized by intermediary octane numbers (even 9.2 more than 100 if the mixture contains compounds better than isooctane) Ex : A mixture of 90% isooctane with 10% heptane has an octane number of 90. • The pollutants produced by burning gasoline could be eliminated if the combustion happened in ideal conditions in which isooctane would be involved only in the heat producing oxidation into carbon dioxide and water: • As we learned, carbon dioxide has its own damaging effects in the context of global warming, but it is however part of the natural content of the atmosphere C 8 H 18 + 25O 2 16CO 2 + 18H 2 O + energy isooctane + oxygen carbon dioxide + water + energy
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Automobile Emissions – Pollutants 9.2 • In reality, alkanes are also involved in other types of reactions… • For instance, isooctane also enters in similar heat producing reactions following a different pathway and resulting into pollutants such as carbon monoxide : • Moreover, since the necessary oxygen is extracted from the atmosphere which is made of about 78% nitrogen, the heat produced by burning the gasoline favors the C 8 H 18 + 25O 2 14CO 2 + 2 CO + O 2 + 18H 2 O + energy isooctane + oxygen carbon dioxide + carbon monoxide + oxygen + water + energy production of nitrogen dioxide and nitrogen oxide : Quiz : Do you recall why these oxides are pollutants? • The polluting compounds of nitrogen with oxygen are called NOX
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L09 - Chapter 9: Automobiles Motivation. Car engine cycle...

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