Abstract: The stable and pulse spray characteristics of a type of bi-centrifugal swirl injector were studied experimentally with particle dynamic analyzer.Properties of droplets such as velocities,size distribution,and volume flux were measured.The results show that the two sprays produced separately by the inner and outer nozzle converged to form one spray,which was as same as that of a simplex injector.The distributions of velocities, mean diameters and volume flux showed hollow cone spray characteristics.The velocities distributions of pulse spray were identical to that of stable spray,but the distinct difference was the RMS velocities were bigger than the mean velocities at the center zone of pulse spray.The Sauter mean diameters of pulse spray are bigger than that of stable spray.The poor atomization is due to the unstable and discontinuous liquid film formed in each nozzle at pulse conditions.The experimental results can provide important references to injectors design.