Abstract: The valveless scheme has been verified to be able to produce high-frequency detonations because it eliminates mechanical valves, which is believed to be setting a ceiling frequency of intermittent supplies of fuel, oxidizer, and purge gas. However, the highest detonation frequency achieved under such a scheme does not exceed 150 Hz. In order to further investigate this scheme utilizing liquid fuels and its possibility to produce detonations in a higher frequency, gasoline has been employed to verify whether high-frequency detonations can be obtained with and without the purge process. The influences of filling pressure, oxygen volume fraction, and injection conditions on the initiation and propagation characteristics of high-frequency detonations have been studied experimentally. The results show that using gasoline can achieve high-frequency detonations under the valveless and purgeless scheme, and the valveless and purge scheme. The highest frequencies achieved are 300 Hz and 210 Hz respectively. When the oxygen volume fraction is 40% and 50% in the valveless and purgeless scheme, the corresponding ranges of the equivalence ratio to produce stable detonations are 0.90-1.49 and 0.74-1.82, respectively, while the range of the equivalence ratio is 0.95-1.61 in the valveless and purge scheme. It is concluded that the valveless and purge scheme can effectively reduce the appearance of deflagration, and the upper limit of the equivalent oxygen volume fraction to ensure stable operation is 58%. The key to producing high-frequency detonations is to form an effective buffer zone in valveless scheme. Oxygen-poor or fuel-poor mixtures can replace common inert gases as purge gas.

Key words: detonation, high frequency, valveless scheme, purge gas, liquid fuel