How the gasoline impurities lower the performance?
Answer:
Most gasoline is heptane. If you get some hexane in there the hexane will pre-ignite when it hits the hot surfaces of the combustion cylinder during compression but before ignition (knock).
Octane is a bit of a misnomer. It comes from and old chemical that was put in to prevent this pre-ignition, tetra ethyl lead. Some folks used to call this stuff octane, because it had 8 carbons. Then they decided (for the 10th time) that lead is bad. They started adding other higher molecular weight alkanes (C8 – C10) to create the same effect as the tetraethyl lead. These high molecular weight compounds do not vaporize as easily inside the cylinder, and create a cooling effect. This cooling minimizes the pre-ignition.
BTW ever heard your car continue to run after the key is turned off? This is called “dieseling”. And it can be caused by a build up of these octane boosters in the cylinder.
As far as performance goes. If the fuel burns before the piston reaches the power stroke, you are loosing power. If the fuel burns after the power stroke has concluded (valve opens) you are loosing power.
How do?
The gasoline doesn't burn as efficiently during combustion... so you get less power out of the cycle.
the impurities do not have the same properties as the gasoline itself. they do not "fire" (explode) under the same conditions as the gas. when there is incomplewte burn on the gas, typically you get "knocking" and "pinging" in the engine
it doesnt burn efficiently, and octane (an impurity) causes engine knock!!
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