Patent Application
20100025500
The present disclosure is directed to a fuel injector and, more particularly, to materials for a fuel injector.
As government regulations for exhaust emissions become more stringent, manufacturers may have to develop combustion engines that produce emissions that are lower than current levels. One method for reducing combustion engine emissions is to use more efficient engines having higher fuel injection pressures and temperatures such as, for example, engines having direct injectors with small orifice sizes. Higher combustion temperatures and pressures may cause conventional fuel injector materials to soften and/or be excessively stressed, possibly leading to improper operation. Because fuel injector components are subjected to a high number of load cycles during a design life such as, for example, billions of load cycles, fatigue failure of current materials due to higher temperatures and pressures may be particularly problematic.
U.S. Pat. No. 6,168,095 (the '095 patent) issued to Seitter et al discloses the particular materials used in forming a portion of a fuel injector. The '095 patent discloses a fuel injector for an internal combustion engine having a nozzle body that supports a movable valve needle. An outer surface of the nozzle body facing the combustion chamber and an inner surface of the nozzle body supporting the valve needle are hardened with the use of nitrogen.
Although the fuel injector of the '095 patent may provide materials for a fuel injector, it may fail to prevent softening and fatigue failure at the higher pressures and temperatures required to increase engine efficiency and to reduce exhaust emissions to required levels.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in the art.
In accordance with one aspect, the present disclosure is directed toward a fuel injector. The fuel injector includes an injector body and an injector needle located inside the injector body. At least one of the injector body and injector needle has a portion configured to be exposed to a combustion chamber, the portion including maraging or carburizing steel and having a nitrided outer layer.
According to another aspect, the present disclosure is directed toward a method for processing a fuel injector component. The method include machining at least a portion of a fuel injector component formed of maraging steel and nitriding the fuel injector component during an aging process.
Fuel injector 125 may inject fuel directly into combustion chamber 120 without pre-mixing the fuel with air prior to injection via an intake manifold. Because fuel injector 125 may directly inject fuel into combustion chamber 120, a portion 130 of fuel injector 125 may be exposed to combustion chamber 120.
Referring to
Body portion 135 and/or needle 140 may be made from a maraging steel. As is known in the art, the maraging steel is an iron-based alloy that may undergo a martensitic transformation. The martensitic transformation may be followed by age or precipitation hardening that may increase strength, ductility, and toughness of the maraging steel. Body portion 135 and/or needle 140 may be made from any suitable maraging steel such as, for example, C-300 or C-350 maraging steel. Body portion 135 and/or needle 140 may alternatively be made from AerMet alloys 310 or 340. It is contemplated that additional components of fuel injector 125 may be made from maraging steel.
Maraging steel for body portion 135 and/or needle 140 may be subjected to vacuum induction melting and vacuum arc remelting to reduce oxide content in the steel. Vacuum induction melting may include melting metal within an airtight water-cooled steel furnace under vacuum conditions via an induction of electrical eddy currents. Vacuum arc remelting may include a drop-by-drop melting and casting in a vacuum-sealed furnace. Vacuum induction melting and vacuum arc remelting may remove undesirable gases such as oxygen, nitrogen, and hydrogen, and each process may have a duration such as, for example, of up to about 24 hours. Vacuum induction melting and vacuum arc remelting may lower the probability of subsurface fatigue crack initiation in the steel.
Body portion 135 and/or needle 140 may alternatively be made from a carburizing steel. As is known in the art, carbon may be added to low-carbon steels at high temperatures such as, for example, 850° to 950° Celsius to form the carburizing steel. Body portion 135 and/or needle 140 may be made from any suitable carburizing steel such as, for example, Ferrium C61. It is contemplated that additional components of fuel injector 125 may be made from carburizing steel.
In addition to being made from maraging steel or carburizing steel, body portion 135 and/or needle 140 may be nitrided to provide compressive residual stresses. The combination of nitriding with maraging or carburizing steel may produce a unique reaction in a surface layer. Nitriding a maraging steel or a carburizing steel may produce a surface layer having significantly higher beneficial compressive residual stresses than may be produced by nitriding conventional materials. The compressive residual stresses may resist fatigue stresses from high engine temperatures and pressures during a service life of fuel injector 125. As is known in the art, nitriding may be a thermochemical diffusion treatment that diffuses nitrogen into a surface of a ferrous material without changing the microstructure of the material. Nitriding may generally result in a layer of a nitrided component being a predominantly γ′ compound (Fe4N), a predominantly ε compound (Fe2-3N), or a mixture of γ′ and ε microstructures. An outer surface 150 of body portion 135, an inner surface 155 of body portion 135, a surface 160 of needle 140, and/or a surface 165 of orifices 145 may be nitrided. It is contemplated that additional components of fuel injector 125 may also be nitrided.
The disclosed fuel injector may be used in any machine where fuel is injected at high pressure such as, for example, a machine having an internal combustion engine. The disclosed fuel injector may substantially resist failure at high temperatures and pressures in such machines.
Components of fuel injector 125 that are exposed to combustion chamber 120 may be made from maraging steel and may be nitrided. As illustrated in
As noted above, components of fuel injector 125 that are exposed to combustion chamber 120 may alternatively be made from carburizing steel and may be nitrided. As illustrated in
Components of fuel injector 125 made from carburized or maraging steel, and nitrided according to the disclosed method, may provide a fuel injector capable of withstanding high temperatures and pressures associated with internal combustion engines. Fuel injector 125 may thus substantially resist fatigue failure at such high temperatures and pressures.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed materials. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed method and apparatus. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
