The flame turret is a unique item that is difficult to find many applications for. It mostly finds it's way into 'trap bases', where a player is locked in a tight space and is burnt to a crisp by this monster.
It functions similarly to an Auto-Turret, activating only when a player without building privilege wanders in front of it. It then rotates rapidly, spewing a wall of flame in about a 30° angle in the general direction of the target until the target is dead or gone.
The flame turret is fueled by low grade fuel, and has a relatively short range to it's flames. Thus, this is a trap that requires a fair bit of planning for you to make good use of, but can be a powerful ally if you do.