Every car must use proper fuel that is suitable with its engine specification. Compression ratio of an engine defines the right fuel to be used. Using improper gasoline is wasteful and can create a ‘knocking’ or ‘pinging’ sound from car engine. That's why choosing the right fuel for your car is very important.
What Is Octane?
Octane number is a standard measure showing maximum pressure allowed in combustion chamber before gasoline is combusted spontaneously. A mix of air and fuel in an engine combustion chamber can spontaneously burn before ignition by spark plug. Lower octane number means longer time for gasoline to combust spontaneously. Nonspontaneous combustion causes a knocking or pinging sound from car engine. This must be avoided at any price by using higher octane gasoline. You can choose the right fuel for your car based on suggested octane number that is suitable with compression ratio of your car engine. It’s advisable that engines with high compression ratio use high octane gasoline.
What is Compression Ratio?
Compression ratio is the ratio of volume of cylinder when the piston is at the top dead center to bottom dead center. Higher compression ratio makes the air and fuel particles compressed in larger density and in high pressure, thus more fuel is combusted. Take a 4-cylinder gasoline engine with each cylinder containing 500 cc for an instance. When the piston is at bottom dead center, each cylinder is completely filled with 500 cc of air and gasoline, but when the piston is at top dead center, the volume is 50 cc. It means that the compression ratio is 1:10.
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Proper Fuel Based On Compression Ratio
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The following are examples for use of proper fuel for different engine’s compression ratios:
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87 Octane
It’s called regular gasoline in America and other countries. In Indonesia, the regular gasoline is of 88 octane, known as Premium gasoline. Gasoline with this octane number is proper for engines with compression ratios of 7:1 to 9:1.
90 Octane
In Indonesia, gasoline with this octane number is branded Pertalite, which is good for engines with compression ratios of 9:1 to 10:1.
92 Octane
Gasoline with this octane number is known in Indonesia under the brands Pertamax (produced by Pertamina), Super (produced by Shell), and Primax (produced by Petronas). This type of gasoline is advisable for car engines with compression ratios of 10:1 to 11:1.
95 Octane
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Gasoline with this octane number is known in Indonesia under the brands Pertamax Plus (produced by Pertamina), Super Extra (produced by Shell), and Primax (produced by Petronas). This type of gasoline is advisable for car engines with compression ratios of 11:1 to 12:1. Pertamax Plus is no longer produced today and has been replaced by Pertamax Turbo of 98 octane.
98 Octane
In Indonesia, gasoline with this octane number is branded Pertamax Turbo (produced by Pertamina) and is advisable for engines with compression ratios above 12:1. The price is relatively affordable for gasoline of 98 octane.
These are some consequences if you use fuel that is not suitable with engine’s compression ratio:
- When engine with high compression ratio is given lower octane gasoline, it will cause bad effects to the engine and its performance.
- When engine with low compression ratio is given higher octane gasoline, it will be wasteful because the fuel won’t combust optimally, creates minimum power but with maximum pollution. Lower octane fuel evaporates and burns easily compared to that of higher octane number.
- It’s better for car engine with low compression ratio to use gasoline of low octane number. Forcing the engine to consume higher octane gasoline will only generate bad results. Fuel is not burned well during combustion process, hence leads to lost power. Other effects include high pollutant level emitted by the car.
- When engine with high compression ratio uses lower octane fuel, gasoline in the combustion chamber will be ignited before the spark plug fires, which is called pre-ignition. Besides creating power that is not maximum, this also produces high level of fuel emission and can damage the engine’s main components.
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If you use improper octane gasoline continually, you might get holes in your car engine pistons. The engine will always have knocking trouble every time the car starts or even when the car is pushed to accelerate and precede other cars. It gets worse if the car is often used to travel long distance.
You can check on your car owner’s manual to know about your car engine’s compression ratio. Do not choose fuel only for prestige. Choose proper fuel that is suitable for your car engine specifications. After you choose the right fuel, let's do the right tips how to save fuel for your car!
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