NiTiNb PLUGS FOR SEALING HIGH PRESSURE FUEL PASSAGES IN FUEL INJECTOR APPLICATIONS

A typical heavy-duty diesel fuel injector comprises of a solenoid control valve, a plunger cylinder and a fuel passage linking the first two elements. Through this passage a fuel communication is established where the fuel is delivered into the plunger cylinder via control valve. The plunger pressurizes the fuel in excess of 32,000 psi and the high-pressure fuel is injected through spray nozzle into engine combustion chamber. During manufacturing, this fuel passage is drilled from the outside of injector body, creating an open end that requires sealing at the end of the manufacturing process. Conventional sealing method utilizing a brazed steel plug often fails under prolonged exposure to extreme cyclical pressures. The present paper describes an alternate sealing method utilizing a heat-to-recover NiTiNb plug that offers a more reliable seal and can be installed at much lower temperatures than a brazed steel plug. NiTiNb sealing plug are manufactured from rods that are longitudinally stretched to have a reduced diameter. The stretched rod is then cut and ground to a finished diameter of high precision. During installation, the plug is inserted into the open end of fuel passage and heat is applied to induce shape recovery of the NiTiNb plug. Stress generated from constrained recovery thus creates a tight seal around the cylindrical surface capable of withstanding extreme cyclical pressures.