Gasoline is one of the most common fuels used to power scooters, motorcycles, cars, lawnmowers, boats, and other machinery. More specifically, it is used in spark-ignited internal combustion engines.
It contains petroleum (naturally occurring liquid found beneath the Earth’s surface) and various other organic compounds (as additives) to enhance the engine’s performance. Typically, it’s a homogeneous mixture of hydrocarbons with 4-12 carbon atoms per molecule.
Its composition varies according to climate and environmental regulations. However, gasoline generally contains
- 40% C4 – C10 branched alkanes
- 25% aromatics
- 15% C4 – C8 straight alkanes
- 10% cycloalkanes
- 10% straight-chain and cyclic alkenes
Liquid heptane and isooctane (2,2,4-trimethylpentane) are the two major components of gasoline.
Commercial gasoline is made to meet certain engine performance specifications. While numerous different compositions are possible, most gas stations in the US sell three main grades of gasoline based on the octane ratings.
What Is Octane Rating?
The octane rating shows the ability of a fuel to avoid knock. Modern drivers aren’t familiar with the term ‘knock.’ It is a pinging sound that occurs when fuel is erratically ignited in the engine’s cylinder. It reduces efficiency and could ultimately damage the engine.
In order to prevent knocking, oxygen-containing chemicals, such as ethanol or ETBE, are added to the fuel. This oxygenate is known as octane. Other chemicals are also added to provide fuel system cleaning and control corrosiveness.
There are two octane rating techniques: research octane rating (RON) and motor octane rating (MOR). The former describes the fuel’s behavior in the engine at lower speeds and temperatures. The latter indicates the fuel’s behavior in the engine at high speeds and temperatures.
The octane number is usually the average of these two octane rating techniques. In some countries, the octane rating is defined as the ratio of isooctane to heptane(two major components of gasoline).
The higher the octane rating, the more stable the gasoline. Many people falsely relate octane rating directly to the power output. It has nothing to do with its energy contained. Instead, it simply refers to fuel’s ability to withstand compression before detonating.
Below, we have elaborated the three main grades of gasoline (sold in the US) based on the octane rating.
1. Regular: The lowest octane gasoline
Regular gas (the usual go-to option) contains 87 octane. This means it is composed of 87% isooctane and 13% heptane.
Most car manufacturers recommend regular gasoline. Honda Civic, for example, requires fuel with a minimum octane rating of 87. It is the least expensive of the three grades.
Through improved technology and additives, regular gas has seen significant advancements over the decades to make it a great option for most drivers.
2. Midgrade: The mid-range octane gasoline
Most refineries do not produce midgrade fuels; instead, it is simply created at the fuel station by blending regular and premium gasoline. A 50-50 split of regular and premium gas gives you 89 octane.
This grade of fuel started appearing in the mid-1990s when gasoline was being phased out. At that time, the majority of retailers were selling leaded (regular) and unleaded (now called regular), and premium unleaded gas. As leaded fuel phased out, retailers were left with three grades of fuel, but only two grades to sell. This is where mid-grade fuel was born.
Some manufacturers recommend filling up the tank with mid-grade gasoline (also known as plus gas). For example, Chrysler 300 5.7-liter V8, Dodge Charger 5.7-liter V8, and Jeep Cherokee 3.2-liter V6 require 89 octane for better performance.
3. Premium: The highest octane gasoline
Costing 30-60 cents more than regular unleaded, premium gas is required by some high-performance and luxury vehicles. In particular, cars with high-compression engines and turbochargers can better utilize high octane fuel to yield better efficiency and performance.
91 octane and 93 octane are the two most common versions of premium gas available at most US gas stations. According to the US Energy Information Administration, premium-grade accounts for nearly 11% of all gasoline sold in the country. This is equivalent to more than 1 million barrels per day. In contrast, over 85% of gasoline sold in the US is regular fuel.
Luxury lines, such as BMW 7 series and Mercedes S class, require premium gasoline. If you use regular fuel when the manufacturers call for premium, you run the risk of engine knocking and poor performance. Over time, this could damage your engine and emission control system. It may also void your warranty.
Frequently Asked Questions
Does premium gas give extra benefits?
No. If your vehicle manufacturer doesn’t explicitly specify the use of premium gasoline, using it won’t give you any better mileage or enhanced performance. It’s better to choose regular gas and save money.
In fact, as per the AAA research, American drivers waste nearly $2 billion every year by using premium gas in vehicles designed to run on regular fuel.
Does premium gas clean your engines?
No matter what you have heard, premium gas won’t do much to clean deposits from the fuel system, especially the valves and injectors. Both regular and premium gasoline contain the same detergent additives that serve to prevent the buildup of engine ‘gunk.’ However, licensed Top Tier fuel retailers use a higher standard of detergent additives than non-Top Tier retailers.
Thus, when it comes to gasoline, ‘premium’ doesn’t always mean ‘better’ if the engine doesn’t require it. If you really want to use higher quality fuel to increase the lifespan of your vehicle, you should select Top Tier gasoline instead of buying a higher-octane one.
Read: 10 Different Types of Batteries | Explained
How to decide between regular vs. premium gas?
Consider your vehicle’s age and weight when choosing between both options. If you have a heavier and older car, truck, or SUV with high-performance engines and you are noticing engine knock, try switching to premium fuel to see if that fixes the issue.
If you are still confused, check your vehicle’s manual to see what grade of gasoline is required for the engine or look at the back of the fuel door to see if the recommended octane level is written there.
By knowing what grade of gasoline your vehicle requires, you can save some money and reduce the risk of damaging your engine.
Can you increase the octane level in gasoline?
Yes. There are two methods for increasing the octane content of gasoline.
- Increase the volume of ethanol
- Increase the volume of gasoline aromatics
Currently, ethanol is the least expensive octane provider. It is widely used to raise the octane level of gasoline up to the labeled octane rating on the gas pump. 84 octane gas, for example, is blended with 10% of ethanol to reach the lowest octane requirement of 87 for retail gas.
Read: 12 Best Examples of Homogeneous Mixtures
Furthermore, ethanol is a cleaner-burning alternative to petroleum-based octane enhancers. It is less toxic and has lower health effects compared to other additives. About 10-15% increase of ethanol content in fuel reduces the cancer risk by 6% (from tailpipe emissions).
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