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Octane rating is the measure of a fuel's ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine.
In the U.S., unleaded gasoline typically has octane ratings of 87 (regular), 88–90 (midgrade), and 91–94 (premium).
You should use the octane rating required for your vehicle by the manufacturer. So, check your owner's manual. For instance, the owner’s manual of a 2018 Altima, states use unleaded regular gasoline with an octane rating of at least 87 AKI (Anti-Knock Index).
Higher-octane fuels resist pre-detonation in the combustion chamber. Vehicles are using higher compression ratios, especially turbo or super charged vehicles, which can lead to pre-detonation of the air-fuel mixture and can reduce performance and fuel economy.
In these engines, high-octane fuel improves performance and fuel economy. Remember this though, when not using a pure gasoline mixture, such as an Ethanol mixture, can have a small trade off in the MPG. Additionally, Ethanol mixtures can add additional stress to the fuel system. Why wouldn’t I just use pure gasoline then? It is not available everywhere, as pure gasoline is more expensive than the Ethanol mixture, and in most cases the cost out weighs the lost MPG. Not covered in this example are the costs associated with the added stresses to the fuel system by using Ethanol-gasoline mixtures.
Power & fuel economy will likely suffer. In addition, using a fuel other than that specified by the owner’s manual could adversely affect the emission control system, and may affect the warranty coverage. Consider the owner’s manual of a 2012 Honda Insight concerning octane minimums: your vehicle is designed to operate on unleaded gasoline with a pump octane number of 87 or higher. Use of a lower octane gasoline can cause a persistent, heavy metallic rapping noise that can lead to engine damage.
It depends. For most vehicles, higher-octane fuel may improve performance and gas mileage and reduce carbon dioxide (CO2) emissions, under more stressful conditions. However, under normal driving conditions, you may get little to no benefit. There will always be a tradeoff between the use of Ethanol mixture & pure gas.
The fuel components that boost octane are generally more expensive to produce.
In some vehicles, you do not get the option. If the vehicle requires midgrade or premium fuel, you will experience the benefit of the higher-octane gasoline, but at the same time, not abiding by the manufacturers recommendation can lead to performance issues. When the owner's manual states the vehicle does not require premium, but states that the vehicle will run better on higher-octane fuel, it is up to you. The cost increase is typically higher than the fuel savings. Is a greener driving experience more important to you than cost? The higher octane rating will reduce CO2 emissions and decrease petroleum usage, which is greener than the lower octane alternatives. But even here there is a cost, as corn crops typically used as food sources are repurposed to produce Ethanol.
Unless you have an older vehicle with a carbureted engine, you should use the manufacturer-recommended fuel for your vehicle; even two AKI can make a difference.
Ethanol has a much higher octane rating than gasoline. Refiners usually blend ethanol with gasoline to help boost its octane rating—most gasoline in the U.S. contains up to 10% ethanol. Blends of up to 15% ethanol are available in some areas, and several manufacturers approve using this blend in recent-model vehicles. Also consult your owner’s manual to know for sure if your car has warnings against its use.
In most states, stations are required to label the pumps if they contain ethanol over a certain percentage, which varies by state but is usually 1 percent. A few states have no labeling requirement, and you just have to ask someone at the station that knows what goes in the tanks.
Pure gas gives better mileage than E10, and much better than E85, simply because gasoline has higher free energy than ethanol. The free energy of gasoline is 34.2 MJ per liter. The free energy of ethanol is 24.0 MJ per liter. That means E10 (10% ethanol) has a free energy of 33.2 MJ per liter, and E85 (85% ethanol) has a free energy of 25.6 MJ per liter. As a result, your mileage is reduced by 3% with E10 over pure gas, and 25% with E85 over pure gas, all else being equal. Mileage will be reduced even more if your engine does not run as well on E10, which is often the case with older vehicles. Learn more about pure gas here.
The measure of a fuel's ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine.
Most vehicles are designed to run on 87 octane, but others require a higher-octane fuel. For example, the 2012 Honda Insight Hybrid requires fuel with a minimum octane rating of 87 while a vehicle like the 2016 Mercedes G-class will requires at least 91 octane. But it allows for use of 87 in a pinch. Consider the following additional notes in a Mercedes G-class owner’s manual: Only refuel using unleaded premium grade gasoline with at least 91 AKI/ 95 RON. Only use the fuel recommended. Operating the vehicle with other fuels can lead to engine failure. Additionally do not use the following:
The best way to know what kind of octane your car needs is detailed in the owner’s manual, or a label on the inside of the fuel cap cover. In some vehicles, it is indicated near the fuel gauge on the dash.
Higher-octane fuels are often required or recommended for engines that use a higher compression ratio and/or use supercharging or turbocharging to force more air into the engine. Increasing pressure in the cylinder allows an engine to extract more mechanical energy from a given air/fuel mixture but requires higher-octane fuel to keep the mixture from pre-detonating. In these engines, high-octane fuel will improve performance and fuel economy. Remember, Ethanol-mixtures do come with a MPG tradeoff.
Because Ethanol has a higher octane rating than gasoline, it experiences reduced engine knocking and improved performance. The main benefit of E10 over pure gas is the cost savings (at the pump). Your vehicle will likely experience 3% or even more of a reduction in MPG, but not enough to offset the savings.
Increased Ethanol is bad for the fuel system, and comes with reduced performance due to lower BTU’s, which translates to less power, and fewer MPG. Ethanol holds up to 50% more moisture than gasoline, which can lead to phase separation. In this situation the Ethanol and water separate from gasoline & settle in the bottom of the tank. This moisture can cause corrosion, and poor cold weather starting. Additionally, the slightly more acidic nature of Ethanol can add to the corrosion process of metal components.
Argonne National Laboratory states, ethanol reduces greenhouse gas emissions between 34 to 44 percent compared to gasoline.
As car manufacturers increase the number of models equipped with high compression engines to maximize performance and efficiency, higher-octane fuels will be required and ethanol is set to play a crucial role. Is this going to lead to more and more fuel system disruptions and damage? Likely. There are a few actions you can perform at each fueling and during the life of the vehicle to decreased the negative effects of Ethanol on the fuel system. Speak with your Shamrock TIre & Auto Repair specialists for more details on what services we offer in order to curb the negative effects of Ethanol on your fuel system. Wichita Mechanic Shop>>
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