How to code a burst of speed?

Hello everyone! I have to code a little burst of speed for my 2D shuttle, and I need some help! So, I got this code

public class ShuttleMovement : MonoBehaviour

{ float speedForce = 10f; float torqueForce = 3f; public ShuttleMovement() { }

 void Start()
 {
     
 }
 void Update() { }
 void FixedUpdate()
 {
     Rigidbody2D rb = GetComponent<Rigidbody2D>();
     if (Input.GetButton("Accelerate"))
     {
         rb.AddForce( transform.up * speedForce);
     }
     rb.AddTorque(Input.GetAxis("Horizontal") * torqueForce);
 }

}

the speedforce is just the normal speed whenever I press W, and the torque is for turning left or right, anyways, what I want is that whenever I press the spacebar, the forwards speed of the shuttle goes up for about 2 seconds, let's say, the normal speed(speedForce) is 10f, but whenever I press the spacebar, it get's up to 15f for about 2 seconds, then it slows down to normal Thanks!