National Petroleum Authority, Ghana

Introduction
Gasoline is the fuel designed for use in spark-ignition internal combustion engines. The bulk of a typical gasoline consists of hydrocarbons (a compound consisting of carbon and hydrogen atoms) with between 5 and 12 carbon atoms per molecule. Gasoline is a mixture of hundreds of hydrocarbons, many of which have different boiling points. Thus gasoline boils or distills over a range of temperatures, unlike say water, which is a pure compound and boils at a single temperature. In certain parts of the world, gasoline is called petrol. Ordinary gasoline, which is a mixture of several compounds, known as hydrocarbons, is derived from refining petroleum crude plus small quantities of few additives to improve its stability, control deposit formation in engines, and modify other characteristics. Sometimes the term “mogas” (motor gasoline) is used to distinguish gasoline from “avgas” (aviation gasoline). In the US, for example motor gasoline is simply called “gas”. The latter is different from liquefied petroleum gas (LPG), one of the refining products of crude oil.

Refining
During the core refining process of crude oil, called simple distillation, several “fractions” are obtained according to differential temperatures of the distillation column. The temperature of the column is highest at the bottom of the column and decreases towards the top. The lighter products - liquid petroleum gases (LPG), naphtha, and so-called “straight run” gasoline - are recovered at the lowest temperatures (at the top of the column). The middle distillates - jet fuel, kerosene and others (such as home heating oil and diesel fuel) are recovered around the mid-section of the distillation column. Finally, the heaviest products (residuum or residual fuel oil) are recovered towards the bottom part of the column. The “straight run” gasoline is later blended to obtain the motor gasoline that is used in internal combustion engines.

Resistance to KnockingThe most important characteristic of gasoline is its octane rating. Gasoline is classified into three main grades according to their antiknock index (octane rating or number) - regular, midgrade and premium gasoline. The octane rating of regular gasoline is greater than 85 and less than 88, while that of midgrade is higher 88 but less than or equal to 90. For premium gasoline, the octane rating is greater than 90. However, most gas stations in developed countries offer three octane grades: regular, usually 87 octane, mid-grade, usually 89 octane and premium, usually 92 or 93.

But what is octane rating or number? Octane rating or number - a characteristic of gasoline - is a measure of the antiknock quality of gasoline; the ability of the gasoline to resist knocking when it is burned in an engine. Knocking, a rattling or pinging sound, is caused when compressed fuel-air mixture detonates prematurely in one or more cylinders. Occasional light knocking or pinging will not harm your engine, and does not indicate a need for higher octane. However, severe knocking must not be ignored as heavy or persistent knocking can lead to engine damage.

In the recent past, filling stations in Ghana sold two grades of gasoline - regular and premium. However, a lone grade of fuel - premium - is the only offering at filling stations in the country at the moment. Thus, the higher the octane number of a gasoline, the greater is its resistance to knock. Iso-octane (octane number 100) and n-heptane (octane number 0) are used as the reference points for octane number. Therefore, an octane number of 91 means that the fuel, when tested in a specified engine and procedure, has the same anti-knock quality as a mixture of 91% iso-octane and 9% n-heptane by volume.

Fuel EconomyGood fuel economy is a combination of good vehicle maintenance and sensible driving. A properly tuned engine, a clean air filter, aligned and balanced front wheels, and tyres with the correct air pressure are maintenance factors that contribute to good fuel economy. Since mistuned engines also result in higher emissions, the onboard diagnostic system in a modern car will alert you to an engine problem. Sensible driving involves smooth, steady acceleration; driving at moderate rather than high speeds on the highway; not carrying a heavy load, using a luggage rack, or towing a trailer unnecessarily; not using the air conditioner excessively, and not idling the engine when it could be turned off. However, some factors that reduce fuel economy are beyond the control of the driver: water, slush, head winds, driving uphill, and driving in stop-and-go traffic. It must be stated that driving with opened windows contributes to poor fuel economy as it increases the drag on the car. The shape or aerodynamic system of a car affects its fuel economy. Cars that are well streamlined, sporty and sleekier have better fuel economy than those that are too “rectangular” in shape.

Relationship between driveability and VolatilityDriveability describes how an engine starts, warms up and runs. It is the evaluation of the response of a vehicle to the accelerator, relative to what the driver expects. Problems associated with driveability include: hard starting, backfiring, rough idling, poor throttle response and stalling. Volatility is the key gasoline characteristic for good driveability. Volatility is the gasoline’s tendency to vaporise. Volatility is important because liquids and solids do not necessarily burn; only vapours burn. When a liquid appears to be burning, actually it is the invisible vapour above the surface that is burning. This rule holds true in the combustion chamber of an engine; gasoline must be vaporised before it can burn. In cold weather, gasoline is blended to vaporise easily. This allows an engine to start quickly and run smoothly until it is warm. In warm weather, gasoline is blended to vaporize less easily in the vehicle to prevent vapour lock or other hot-fuel handling problems and minimize evaporation, which contributes to air pollution. It is important to note that there is no single best volatility for gasoline. Volatility must be adjusted for the altitude and seasonal temperature of the location where the gasoline will be used.

Safety, health and environmental concernsIt is of utmost necessity that gasoline is handled with extreme care, as it is dangerous. Gasoline is highly flammable, easy to ignite and burns explosively. In addition, exposure to gasoline liquid or vapour can cause adverse health effects. To avoid fire outbreaks, do not smoke near exposed gasoline and avoid breathing gasoline fumes. When putting gasoline in containers, ensure that it is only about 95 percent full. This leaves room for gasoline to expand if it warms