98 octane gasoline refers to fuel with an octane rating equivalent to a mixture of 98% isooctane and 2% n-heptane. The advantages of 98 octane gasoline are summarized as "two highs and two lows": higher knock resistance and power output, while containing fewer harmful substances and producing lower exhaust emissions. Engines with high compression ratios should use high-octane gasoline. Using low-octane fuel in high-compression engines can cause abnormal combustion, resulting in knocking, increased fuel consumption, and reduced driving power. Compared to other gasoline grades, 98# gasoline offers superior knock resistance and higher calorific value, delivering stronger performance. However, due to its higher grade and price, it's predominantly used by luxury vehicles and is often referred to as "premium gasoline". Standards: The Chinese government imposes strict standards on automotive gasoline. These standards not only require specific octane ratings (commonly known as gasoline grades) but also regulate the chemical composition of gasoline. Excessive olefin content can lead to incomplete combustion, producing a gummy substance that accumulates in the intake manifold and valve guides. When selecting gasoline grades, factors such as engine operating conditions, altitude, and atmospheric pressure should be considered. Gasoline engines frequently operating under high load, high torque, and low-speed conditions (e.g., towing vehicles) are prone to knocking and should use higher-octane gasoline (compared to vehicles under normal conditions). In high-altitude areas, where atmospheric pressure is lower and air is thinner, the tendency for engine knocking decreases, allowing for the use of slightly lower-grade gasoline. Empirical data shows that for every 100m increase in altitude, the required gasoline octane rating can be reduced by approximately 0.1 units. Note: Vehicles with electronic fuel injection systems generally have compression ratios above 8.0. Imported vehicles labeled as suitable for Chinese market conditions can typically use leaded gasoline; otherwise, they require unleaded gasoline. Generally, higher gasoline grades indicate higher octane ratings and better knock resistance. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. Using higher-grade gasoline in vehicles designed for lower grades won't cause damage, but the increased octane rating alters the fuel's ignition point, potentially causing delayed combustion in the engine. This results in reduced power output and thermal efficiency, manifesting as poorer performance. Using lower-grade gasoline in vehicles designed for higher grades can cause engine knocking. The significantly lower octane rating reduces the fuel's ignition point, causing premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance builds during the upward stroke, leading to unstable engine operation. Mild knocking may only increase noise without significant engine damage, but severe knocking indicates serious engine issues. The vibrations not only affect driving stability but also cause abnormal wear on pistons and cylinders, potentially leading to cylinder scoring in extreme cases.
