Advanced TR-PIV (time-resolved-particle image velocimetry) system was used to measure transient velocity field at a Helmholtz-type valve pulse jet engine exit zone. Test results indicate the cyclical evolution process of velocity field and pressure at the exit zone of valve pulse jet engine

and the maximum time-averaged velocity of the engine is not at the nozzle's exit. The vorticity and duration in the exhaust stage was stronger than that in the inspiratory stage. Measured velocity field shows that transient high-temperature combustion gas does not fully expand at the exit plane

but continues to be expanded at the following exit zone

which is disadvantageous for improving the performance of pulse jet engine.