Particle Emitting Speed Through Script

I have a JS which I try to change the velocity the particles are emitted. (I included full script for you to understand better)

 #pragma strict
 
 var engine: ParticleSystem;
 var thrust: float;
 var thrustRate: float;
 var startThrust: float;
 var fuel: float;
 var F9: GameObject;
 
 function Start () {
     engine = GetComponent.<ParticleSystem>();
     thrust = startThrust;
     fuel = 70;
 }
 
 function Update () {
     if(fuel > 0){
         if(Input.GetKey(KeyCode.LeftShift)){
             if(100 > thrust){
                 thrust = thrust + thrustRate;
             }
         }
         if(Input.GetKey(KeyCode.LeftControl)){
             if(thrust > 0){
                 thrust = thrust - thrustRate;
             }
         }
         fuel = fuel - (thrust * 0.000001);
         F9.GetComponent.<ParticleSystem>().Particle.velocity = thrust;
     }
 }

The problem is this part: F9.GetComponent.().Particle.velocity = thrust;

Console tells me "An instance of type 'UnityEngine.ParticleSystem.Particle' is required to access non static member 'velocity'.

Like I said, I want the particles go faster as I increase "thrust".

(If you ask why do I have sth called "engine", it is bc I tried to use it as engine.Particles.velocity but it didn't work)