A fracturing system for wells has a propellant charge having a known surface area for combustion, and a combustion rate as a function of pressure with lower combustion rates at lower pressures and rapidly increasing combustion rates at higher pressures separated by a knee in the combustion rate function. The propellant charge is initially sealed within a vessel as it is inserted into a well. The system also includes means for creating openings in the vessel on ignition of the propellant charge in the well, such that the openings have a known combined flow area selected to create a condition of choked flow of combustion gases from within the vessel and maintain pressures within the vessel below the knee in the combustion rate function.