Leaded and Unleaded Gasoline
We still see and the word unleaded gas on the gas pumps, but unless you are getting close to 40
years old you may not have hear of or know what the difference between leaded and unleaded gasoline is. Let
me explain.
When cars were first build one of the greatest obstacles was detonation. By definition, detonation in a
vehicle is a secondary explosion that occurs after the spark plug has ignited the fuel mixture in the engines
combustion chamber. Detonation occurs when part of the air/fuel mixture begins to ignite on it own.
The first car engines had a very short life expectancy because of detonation. It was soon discovered that if a
small amount of lead (a couple of grams per gallon) was added to the gasoline, detonation could be significantly
reduced. This combined with better control of ignition timing, engine temperature, and fuel mixture detonation
could be eliminated.
Adding lead to gasoline had another positive affect on engines. The lead going to the engines combustion chamber
coated the engine valve and valve seats. This caused a cushioning affect as the valves opened and closed. This
significantly reduced valve and valve seat wear, which lead to longer engine life.
Unfortunately, the lead that reduced detonation and extended engine life was not consumed by the combustion
process. It passed through the engine and was expelled out the exhaust system in to the atmosphere. Lead as you
probably know is a deadly poison and for the better part of 60 years our cars were filling the air we breathe with
it. It was not until the early 70’s that the government finally mandated that lead be removed from gasoline.
Because car engines were design and built to operate on leaded gas car makers had to redesign engine to
operate on gasoline without lead in it. Older car would still need it. For these reasons lead was not completely
removed but slowly removed over a period of years. It was not until the late 80’s that lead was completely
disappeared from all gasoline. No longer can you purchase leaded gasoline. Since the disappearance of leaded gas in
the United States the blood-lead level of the American population is said to have declined more than 75
percent.
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