图为不同粒径粒子的速度与轴向距离关系图。实线表示2 MPa二次注氮压力下的焰流速度变化，点线表示不同粒径粒子的速度变化。

在粒子飞行的前半段，当粒子的速度小于焰流速度时，拖拽力作为驱动力推动粒子的运动，此时粒子处于加速运动状态。对于刚射入的粒子来说，粒子速度与焰流速度差较大，气体作用于粒子表面的拖拽力较大，粒子速度的提升较为明显；对于刚飞离喷口处的粒子，随着粒子不断的加速，粒子速度与焰流的速度差逐渐缩小，粒子速度的提升逐渐平缓。

在粒子飞行的后半段，空气域中的气体透过射流边界层与焰流掺混，使轴线处的焰流速度开始迅速下降，随着焰流速度的不断降低，当粒子速度小于焰流速度时，原来作为驱动力的气体拖拽力变为阻力，促使粒子的速度开始下降，而粒子由于惯性作用，速度保持性相对于焰流更强，粒子速度下降的趋势相对于焰流较缓慢。

从图中可以看出，直径为10 μm的粒子在射离喷嘴后不断加速直至最大速度（1110 m/s），后因空气阻力作用速度不断减小。而20-70 μm的粒子加速到最大值后，速度的降速较为缓慢。综上所述，粒径较小的粒子很容易获得最大速度，但也正因为其惯性小、阻力大，它们不能保持速度的稳定性。粒径较大的粒子速度峰值较小，却在后半程的飞行过程中速度维持性较好，喷涂距离对较大粒径的粒子速度影响也较小

The graph shows the velocity versus axial distance of different particle sizes. The solid line indicates the velocity change of the flame flow under the secondary nitrogen injection pressure of 2 MPa, and the dotted line indicates the velocity change of different particle sizes.

In the first half of the particle flight, when the particle velocity is less than the flame flow velocity, the dragging force acts as the driving force to push the particle motion, and the particle is in the accelerated motion. For the newly injected particles, the difference between particle velocity and flame velocity is large, and the drag force on the particle surface is large, so the increase of particle velocity is more obvious; for the particles just flying away from the nozzle, as the particles continue to accelerate, the difference between particle velocity and flame velocity is gradually reduced, and the increase of particle velocity is gradually leveled off.

In the second half of the particle flight, the gas in the air domain mixes with the flame through the jet boundary layer, so that the flame velocity at the axis starts to drop rapidly, and as the flame velocity decreases, when the particle velocity is smaller than the flame velocity, the dragging force of the gas, which is the driving force, becomes the drag force, and the particle velocity starts to drop, while the particle velocity decreases more slowly than the flame velocity due to the inertia, and the velocity retention is stronger than the flame velocity. The tendency of particle velocity decrease is slower than that of flame flow.

From the figure, it can be seen that the particles with a diameter of 10 μm are accelerated until the maximum velocity (1110 m/s) after they leave the nozzle, and then the velocity decreases due to the air drag. While 20-70 μm particles accelerated to the maximum value, the speed of the drop in speed more slowly. To sum up, the particles with small particle size can easily obtain the maximum speed, but also because of their small inertia and large resistance, they can not maintain the stability of the speed. Particles with larger particle size have smaller peak velocity, but the velocity is better maintained in the second half of the flight, and the spraying distance has less effect on the velocity of particles with larger particle size.