Cadillac CT5 has a fuel tank capacity of 66 liters, and the manufacturer recommends using 95-octane gasoline. Currently, gasoline is classified into four grades: 89 (formerly 90), 92 (formerly 93), 95 (formerly 97), and 98 (a newly introduced grade). These numbers represent the octane rating of the gasoline, indicating its anti-knock properties, and are unrelated to the cleanliness of the gasoline. It is more scientific and economical to refuel according to the engine's compression ratio or the requirements specified in the user manual, as it allows the engine to operate at maximum efficiency. During the design phase of an automobile engine, the fuel grade is determined based on the compression ratio. Engine Compression Ratio: The compression ratio is a very important structural parameter of an engine, representing the ratio of the gas volume when the piston starts compression at the bottom dead center to the gas volume when the piston finishes compression at the top dead center. In terms of power and economy, a higher compression ratio is generally better. A high compression ratio results in better power performance, higher thermal efficiency, and corresponding improvements in vehicle acceleration and top speed. However, due to limitations in cylinder material performance and gasoline combustion knock, the compression ratio of gasoline engines cannot be too high. High-compression-ratio vehicles require high-grade fuel. The higher the fuel grade, the slower the combustion speed and the lower the combustion knock, requiring the engine to have a higher compression ratio. Conversely, low-grade fuel has a faster combustion speed and higher combustion knock, requiring the engine to have a lower compression ratio. The fuel grade also relates to the engine's ignition timing. Low-grade gasoline burns faster, requiring a delayed ignition angle, while high-grade fuel burns slower, requiring an advanced ignition angle.
