Because wa made two significant assumptions, this equation is a highly idealized model for the comebustion of gasoline. The use of octane to represent all of the hydrocarbon in gasoline is mainly for simplicity. If we chose to, it would not be very difficult to write similar combustion equation for each hydrogen that is actually present. But the assumption og complete combustion is more drastic. You probably know that typical automobile exhaust contains a number of compounds besides carbon dioxide and water vapor.Most states require periodic emissions testing to measure the levels of carbon monoxide and hydro carbons in a car's exhaust, and some states or local areas also require additional tests for other types of compounds.