Device and method for measuring fuel octane number of spark-ignition engine

The invention relates to a fuel testing instrument, in particular to a device and a method for measuring fuel octane number of a spark-ignition engine. Comprising a variable-compression-ratio engine, the compression ratio is changed through the volume ratio, and a knock sensor is arranged on the variable-compression-ratio engine and used for detecting knock signals generated by different fuel-air ratios and different compression ratios in real time; the three-speed motor is in driving connection with the engine with the fixed compression ratio and can reproduce high, medium and low speeds of the engine; the linear variable worm gear pressure increasing and reducing system changes the compression ratio according to the mass ratio. The compression ratio can be changed according to the volume ratio so as to adjust the height of the cylinder, and the compression ratio can also be changed according to the mass ratio so as to adjust the air inflow and flexibly select according to different actual working conditions