For a flow emitter, the time interval (>= 0) between particle flow cycles in ms. A value of 0 means there is one particle flow cycle for each logic update (the maximum flow frequency). This is the default setting. For an exploding emitter, this value will be -1. Calling Phaser.GameObjects.Particles.ParticleEmitter#flow also puts the emitter in flow mode (frequency >= 0). Calling Phaser.GameObjects.Particles.ParticleEmitter#explode also puts the emitter in explode mode (frequency = -1).