◀ Residual fuel includes refinery fuel oil. Other includes bitumen, lubricants, waxes, still gas, coke, sulphur, direct use of crude oil, etc.
46 Topic 7 Fossil Fuels and Carbon Compounds Petrol Petrol is a light fraction of petroleum which is quite volatile and burns rapidly. It is used in internal combustion engines such as motor vehicles, excluding aircraft. The important qualities for petrol include octane number (antiknock) and volatility. Knocking is something we want to try to prevent in petrol engines. It occurs in four stroke engines when some hydrocarbons ignite too early. It causes a knocking sound and reduces the engines performance. We measure the problem using the octane number. The higher the number, the better the fuel. A fuel with a low octane number is likely to cause knocking. One with an octane number over ±00 should be fine. The addition of tetraethyllead(IV) to retard the combustion was initiated in the ±930s but was discontinued in the ±980s because of the toxicity of the lead compounds discharged in the combustion products. Petrol used in automobiles boils mainly between 30 °C–200 °C, the blend being adjusted to altitude and season. For example, in hotter climates, petrol components of higher relative molecular masses with lower volatility are used. Naphtha Naphtha is a basic feedstock for the petrochemical industry (e.g. ethene manufacture, town gas production). Kerosene Kerosene comprises petroleum distillate intermediate in volatility between petrol and diesel oil. Kerosene finds considerable use as a jet fuel and around the world in cooking and space heating. When used as a jet fuel, some of the critical qualities are: • freeze point; • flash point (the lowest temperature at which a volatile fuel produces enough vapour to form an explosive mixture when it comes in contact with a flame); and • smoke point (the maximum flame height in millimeters at which a kerosene will burn without smoking). Commercial jet fuel has a boiling range of about ±90 °C–274 °C. Kerosene, with less-critical specifications, is used for lighting, heating, solvents and blending into diesel fuel. Diesel oil Diesel oil is used as fuel for diesel engines. Its ignition point is much higher than that of petrol. Several grades of diesel fuel are manufactured — for example, ‘light-middle’ and ‘middle’ distillates for high- speed engines with frequent and wide variations in load and speed (such as trucks and automobiles) and ‘heavy’ distillates for low- and medium-speed engines with sustained loads and speeds (such as stationary engines). Criteria for grading diesel oil include ease of ignition, ease of volatilization, and sulphur content. The highest grades, for automobile and truck engines, are the most volatile, while the lowest grades, for low-speed engines, are the least volatile, leave the most carbon residue, and commonly have the highest sulphur content.
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