ParticleSystem.TextureSheetAnimationModule.speedRange

Description

Specify how particle speeds are mapped to the animation frames.

If a particle is travelling slower than the minimum speed, it uses the first frame. If a particle is travelling faster than the maximum speed, then it uses the final frame. For all other speeds, the particle chooses a frame based on how far between the minimum and maximum value its speed is.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    private ParticleSystem ps;

    void Start()
    {
        ps = GetComponent<ParticleSystem>();

        var textureSheetAnimation = ps.textureSheetAnimation;
        textureSheetAnimation.enabled = true;
        textureSheetAnimation.speedRange = new Vector2(0.9f, 5.0f);
    }
}