Influence of Methanol-Gasoline Blends on Vibration Characteristics of Spark-Ignition Engine at Different Speeds

Abstract

This study analyzes the effect of methanol blending in gasoline on a spark-ignition engine's spectrum and vibration response at various operating speeds. Two fuels used are G100 (pure gasoline) and G95M5 (95% gasoline + 5% methanol). Tests were conducted at speeds of 2000 rpm, 2500 rpm, and 3000 rpm using a vibration sensor to obtain acceleration data in the frequency and time domains. The spectrum analysis results show that at 2000 rpm, G95M5 fuel produces a peak vibration acceleration of 0.28 m/s², higher than G100, which only reaches 0.18 m/s². At 2500 rpm, the difference is still visible, with G95M5 reaching 0.19 m/s², while G100 is 0.16 m/s². However, at 3000 rpm, the difference between the two fuels becomes smaller, with the peak acceleration almost the same, which is 0.032 m/s². Time domain analysis shows a similar trend: at 2000 rpm, G95M5 fuel produces a maximum vibration spike of 0.22 m/s², while G100 is only 0.15 m/s². At 2500 rpm, the vibration of G95M5 is still higher, but it starts to decrease at 3000 rpm with a peak value of 0.028 m/s² for G95M5 and 0.026 m/s² for G100. These results indicate that methanol blending increases vibration at low to medium speeds, but the effect is more damped at high speeds. Thus, although G95M5 can improve combustion efficiency, the increase in vibration at low speeds should be considered because it can affect the reliability and service life of engine components in the long term.