1：Did you know?
Currently, gasoline in the market is labeled with grades such as 90, 93, 95, 97, etc. These numbers represent the octane rating of gasoline, which indicates its resistance to knocking and has no direct correlation with its cleanliness. Refueling according to the requirements stated in the vehicle's manual is more scientifically and economically sound, while also allowing the engine to operate at its optimal efficiency.
2：Related Terminology
Compression Ratio:
The primary criterion for selecting the grade of gasoline is the compression ratio of the engine, which is also a key energy-saving indicator for modern automobiles. The engine's operation is composed of a repetitive cycle of "intake-compression-combustion-exhaust-intake" of the cylinder. The ratio between the cylinder volume at the farthest and nearest points of the piston's stroke is known as the compression ratio. The most effective and cost-efficient method to reduce fuel consumption is to increase the engine's compression ratio.
Knocking and Knock Resistance:
It is generally believed that when the piston reaches a point approximately 10 degrees after the top dead center of its stroke, where the combustion generates the highest pressure, the force pushing the piston is at its maximum. For example, at 1000 revolutions per minute (RPM), the combustion process corresponds to about 20 degrees of crankshaft rotation, meaning that ignition should occur 10 degrees before this point to achieve the most efficient engine operation. However, as the RPM increases, the piston moves faster, and the combustion process corresponds to a larger crankshaft angle. Therefore, the ignition timing needs to be advanced by a greater degree, typically 50 degrees in the case of 4000 RPM. Eventually, there is a certain RPM at which the fuel mixture ignites before the spark plug fires, leading to knocking.
3：Some Suggestions
While 93-octane fuel is approximately 5% more expensive than 90-octane fuel, it also provides around 5% lower fuel consumption. From a cost perspective based on fuel consumption per 100 kilometers, they are theoretically equivalent. However, when a high compression ratio engine designed for 93-octane fuel is fueled with 90-octane fuel, it may experience phenomena such as secondary combustion and incomplete combustion, resulting in an additional loss of 5-8% of power. Considering the increased maintenance costs, decreased vehicle performance, and reduced lifespan, the cost of using lower-grade fuel accumulates.
