Abstract: An apparatus and method for injecting pressurized fluid into a well are disclosed. The apparatus to inject pressurized fluid into a well comprises a combustion chamber, having a coolant jacket positioned to circulate coolant over outer walls of the combustion chamber and into the combustion chamber around the burner such that vapor flows between a flame and inner walls of the combustion chamber. The injected coolant forms a vapor barrier between the flame and the combustion chamber walls and is pressurized for delivery into a well. The combustion chamber can be affixed to the well casing at the surface or the combustion chamber can be used as a "down-hole" vapor generator apparatus.