For those who don't speak gasoline-ese, here's a glossary of some of the most common technical terms, to help make all that technical bafflegab a little bit easier to understand. RON, MON and Road Octane: RON stands for a fuel's Research Octane Number. This value is measured under fairly easy test conditions. The MON, or Motor Octane Number, is a tougher test measured at higher engine speed and temperature. And the Road Octane Number - the octane number that relates most closely to actual driving conditions - is the average of these two values, i.e. Road Octane = (RON + MON)/2. The Road Octane Number is more frequently referred to simply as the octane number. Always be sure that the octane number a vendor advertises is its Road Octane value, not its RON. Anti-Knock Index (AKI): The same as the Road Octane Number. It is a numerical description of a fuel's ability to resist engine knocking. Anti-knock index is a more accurate description than octane number, which is why in the U.S. fuels are often given an anti-knock index instead of an octane number. Additives There are four basic types of performance additives in quality gasoline: - Detergents:
These remove and prevent deposits such as carbon in the engine's intake system. - Octane Enhancer:
Lead used to be added to gasoline as an octane enhancer. The common octane enhancers include MTBE (methyl tertiary-butyl ether), MMT (methyl-cyclopentadienyl manganese tricarbonyl), and alcohols. - Oxidation, Corrosion and Rust Inhibitors:
These are designed to prevent formation of gums in gasoline during storage. They also help protect the fuel system parts from rust. - Demulsifiers:
These ensure water separates rapidly from gasoline, reducing the risk of customers finding water in the gasoline they buy at the pump.
Driveability If a gasoline provides good driveability for a vehicle, it is providing the correct balance between starting, gas mileage, smoothness of operation, anti-knock performance and ability to control and prevent engine deposits. A gasoline must be blended so that no single aspect of driveability is sacrificed to achieve another. The result: A vehicle that consistently performs to the manufacturer's specifications. Knocking Knocking occurs when unburned vapours spontaneously explode before the flame reaches them. This results in one or more secondary detonations (in addition to the one created by the spark from the spark plug) instead of one smooth, efficient charge that provides the best mileage. Knocking creates a characteristic rattling or pinging sound from the engine. It reduces fuel economy, and in severe cases can cause engine damage. Iso-octane Often and misleadingly referred to in industry jargon simply as "octane", which results in confusion with a fuel's octane number or anti-knock capability. Iso-octane is an actual substance. An engine's octane number is determined by comparing a test engine's knocking (or lack of knocking) while burning a measured blend of iso-octane, whose octane equivalent is arbitrarily defined as 100, and n-heptane, whose octane equivalent is zero. To avoid confusion, remember that you can pour iso-octane but you can't pour octane because it's simply a number. Specifications These are standards drawn up for gasoline. Some - such as those for vapour pressure and octane number - are established by the Canadian General Standards Board and are generally quoted in provincial regulations. Shell considers these specifications to be a minimum and often exceeds them. Shell also has its own rigorous additional specifications designed to control those properties which we feel will ultimately produce a better gasoline for our customers. Vapour Pressure A numerical measure of the proportion of light hydrocarbons, such as butane, present in the gasoline blend. These hydrocarbons have a lower boiling or vapourization point and are extremely useful for cold weather start-ups. The vapour pressure value is legislated by provincial governments, and can change depending on location and time of year. For example, the allowable vapour pressure at sea-level Vancouver is 62 kilopascals, compared with 72 kilopascals in Ontario. In winter, the government allows higher vapour pressures and more butane in the gasoline blend. Volatility The temperature range over which a fuel vapourizes. It affects startability, combustion, engine deposits, warm-up time, noise, fuel economy and power. Fuels with high volatility evaporate readily in the engine. Fuels with low volatility don't evaporate as easily, so some of the fuel can enter the engine as a liquid. Shell gasolines are blended so that their volatility changes with the season, to ensure the optimum performance of a vehicle's engine.
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