Fuel Octane Rating

Fuel Octane Rating

What is an Octane rating for fuel?

Premium v Regular?

In recent years, car manufacturers have been requiring or recommending premium gasoline (a high-octane grade of fuel) for use in more of their vehicle models. The difference in prices between premium and lower octane grades has also increased. As a result, more people are curious about what octane is and what those octane rating numbers on gas pumps mean.

Multiple Choice

How many carbon atoms are in an octane molecule?

• 6

• 8

• 10

• None of these

Multiple Select

What type of bonds are in octane? (Select all correct answers)

• C=C

• C-C

• C-H

• H-H

Fuel Stability

Octane ratings are measures of fuel stability. These ratings are based on the pressure at which a fuel will spontaneously combust (auto-ignite) in a testing engine. The octane number is actually the average of two different octane rating methods—motor octane rating (MOR) and research octane rating (RON)—that differ primarily in the specifics of the operating conditions. The higher an octane number, the more stable the fuel.

Multiple Choice

A higher octane rating means

• More spontaneous combustion

• More stability

• Less stability

• More engine knock

What type of fuel is in your car?

Retail gasoline stations in the United States sell three main grades of gasoline based on the octane level:

   ~Regular (the lowest octane fuel–generally 87)

   ~Midgrade (the middle range octane fuel–generally 89–90)

   ~Premium (the highest octane fuel–generally 91–94)

Some companies have different names for these grades of gasoline, such as unleaded, super, or super premium, but they all refer to the octane rating.

Poll

If you drive, what type of fuel do you use in your vehicle?

• Regular (87)

• Midgrade (89)

• Premium (91+)

• The cheapest one.

• No vehicle yet, but I'm studying hard to get a good job to buy one some day!

Stable v Unstable

Of the 18 isomers of normal octane (C₈H₁₈), octane gets its name from the 2,2,4-Trimethylpentane compound, which is highly resistant to auto-ignition. This iso-octane has been assigned the reference value of 100 for testing purposes. The extremely unstable normal heptane (C₇H₁₆) molecule is the 0 octane reference fuel.

Multiple Choice

Why does a straight chain heptane have an octane rating of 0?

• It's unstable

• It's not an isomer of octane

• It's unpopular

• It's a hydrocarbon

Multiple Choice

Why does 2,2,4-trimethylpentane have the highest rating of 100?

• It auto-ignites

• It's popular

• It costs $1.00

• It resists auto-ignition

Multiple Choice

Which of these is 2,2,4-trimethylpentane?

• all of these

• none of these

Multiple Choice

Which of these is an isomer of octane?

What's in fuel?

Gasoline is a complex mixture of over 500 hydrocarbons that may have 5 to 12 carbons. Smaller amounts of alkane cyclic and aromatic compounds are present. Virtually no alkenes or alkynes are present in gasoline. Gasoline is most often produced by the fractional distillation of crude oil. The crude oil is separated into fractions according to different boiling points of hydrocarbons of varying chain lengths. 

Poll

Could we live with less crude oil?

• Yes, drive less

• No, it is what it is

• Only during pandemics

• Find alternative energy sources

• No idea

Multiple Choice

Which hydrocarbons boil at lower boiling points?

• Short straight chains, such as propane

• Branched-chains

• Long chains with ~20 or more carbon atoms

• Alkynes

Open Ended

What is something you learned or found interesting from this video?

Multiple Choice

Which is the most appropriate gas to use in your 1990 Mustang?

• E85

• Regular

• Leaded gas from 1990

• Premium

Open Ended

What is something else you learned or found useful from the last video?

Next time you fill up, think about the chemistry involved!

Source for info provided if you want to know more:  https://www.eia.gov/energyexplained/gasoline/octane-in-depth.php