It is a highly branched compound that burns smoothly, with a little knock. On the other hand, heptane is given an octane rating of zero. It is an unbranched compound and knocks badly. Straight-run gasoline has an octane number of about Cracking, isomerization and other processes can be used to increase the octane rating of gasoline to about Anti-knock agents may be added to further increase the octane rating.
Tetraethyl lead, Pb C2H5 4, was one such agent, which was added to gas at the rate of up to 2. The switch to unleaded gasoline has required the addition of more expensive compounds, such as aromatics and highly branched alkanes, to maintain high octane numbers. Gasoline pumps typically post octane numbers as an average of two different values.
One value is the research octane number RON , which is determined with a test engine running at a low speed of rpm. The other value is the motor octane number MON , which is determined with a test engine running at a higher speed of rpm. If, for example, a gasoline has a RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or High octane gasoline does not outperform regular octane gasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine.
However modern high octane fuels may contain additional detergents to help protect high compression engines. Consumers should select the lowest octane grade at which the car's engine runs without knocking.
Occasional light knocking or pinging won't harm the engine and doesn't indicate a need for higher octane. On the other hand, a heavy or persistent knock may result in engine damage. Detailed search. The octane number ON is a measure of the knock resistance of gasoline. It defines a numerical value from 0 to , and describes the behavior of the fuel in the engine during combustion.
In determining the octane number, a distinction is primarily made between the research octane number RON and the motor octane number MON. Research octane number RON The research octane number RON describes the behavior of the fuel in the engine at lower temperatures and speeds, and is an attempt to simulate acceleration behavior. This octane number is posted on pumps in Germany.
See Distillation Oil Refining. The yield of gasoline may be doubled by converting higher or lower boiling point fractions into hydrocarbons in the gasoline range.
See Conversion Refining. Typical Composition of Gasoline General Name Examples Percentage Aliphatic - straight chain heptane Aliphatic - branched isooctane Aliphatic - cyclic cyclopentane Aromatic ethyl benzene What is the octane number? Fuel octane requirements for gasoline engines vary with the compression ratio of the engine. Engine compression ratio is the relative volume of a cylinder from the bottom most position of the piston's stroke to the top most position of the piston's stroke.
The higher an engine's compression ratio, the greater the amount of heat generated in the cylinder during the compression stroke. The net effect is a loss in power, possible engine damage, and an audible "knock" or "ping", referred to as detonation. The octane number of gasoline is a measure of its resistance to knock. In contrast, diesel engines do not compress fuel but rather air and then inject fuel. These engines rely on different ratings, known as cetane numbers.
The main difference between whether or not one uses high or low octane gasoline is determined by the level of "knocking" ones engine experiences.
Inside the engine, an air-fuel mixture is ignited by the spark plug. While this is occurring, the piston is also moving upwards, compressing the air-fuel mixture and simultaneously increasing its temperature since temperature increases as pressure increases. With lower octane fuels, the air-fuel mixture can also ignite due to this compression. When this flame front collides with the flame front ignited by the spark plug, an audible "knock" is heard.
When the air-fuel mixture within an engine ignites due to compression rather than from the spark plug it is known as "pre-ignition" [4] If the fuel combusts and burns before it is ignited by the spark plug, it burns incompletely.
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