4.1.4 CompositionCrude oil and the fuels obtained from it are a mixture ofdifferent hydrocarbon compounds that may roughly be dividedinto paraffins, naphthenes, aromatics and olefins. Other ele-ments, e.g. sulfur, are present in very low concentrations andmust be removed as far as possible during fuel production.The potential range of variations of individual hydrocarbonsincreases as the boiling range increases. While the lightestenergy source, natural gas, only consists of very few and pre-cisely defined hydrocarbons, basically methane, gasoline con-tains more than 200 various hydrocarbons and diesel fuels evensignificantly more because of the frequently present combina-tion of types of hydrocarbons described below. Aromatics havethe greatest variety of paraffinic or olefinic side chains. Hydro-carbons with approximately 10–20 carbon atoms are present indiesel fuels’ boiling range since it is standardized.Unlike spark ignited gasoline engines, diesel engines needhydrocarbons that facilitate good auto-ignition at high pres-sures and high temperatures. These are primarily normalparaffins.
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