Constant pressure, variable thrust bipropellant engine

Abstract

A pressure controlled pintle is employed in combination with a throttling quid, gel, or hybrid engine to provide a constant pressure and variable thrust from a single operating engine. As the propellants are throttled back and the chamber pressure drops, the pintle moves and closes the gap between the pintle and nozzle throat, thereby lowering the throat area and re-establishing the design chamber pressure related to pintle spring tension. By retaining the design pressure over a wide thrust range, the engine efficiency remains at the design value. This eliminates the drop of Isp due to pressure and keeps the cost of the system reasonable because only one engine is required. When a higher thrust is desired, a throttling valve in an injector increases the propellant flow rate, which causes a higher pressure in the combustion chamber. The constant pressure actuator moves the pintle to open the nozzle throat, which reduces the pressure to the design value. The design value may not be optimum. There are many size/temperature/volume trade off's relating to the missile as a whole which could move the design value from optimum. Because the pressure in the combustion chamber remains the same, the Isp is not greatly changed, but the thrust level increases because of the increase in the mass flow through nozzle. The combination provides substantially constant combustion chamber pressure for a single variable thrust bipropellant engine.