Fuel injectors

Fuel injectors inject gasoline or diesel fuel into a combustion cylinder. When the fuel-air mixture is compressed sufficiently, it either ignites spontaneously in a diesel engine or is ignited by a spark from a spark plug in a gasoline engine.

 Gas direct injection, in which the air is first compressed and then fuel is injected into a cylinder, can improve engine efficiency and vehicle miles/gallon, but the fuel must be injected at much higher pressure, usually tens of atmospheres. This means that the seal between the fuel injector surface and the input fuel line must be free of scratches or other defects that could enable fuel to seep out around the edges of the seal and cause a fire in the engine compartment.

 Parts for gas direct injection are usually made of highly polished stainless steel. The part surfaces must be inspected to ensure that there are no scratches or other features that could cause gas leaks. One possible cause of scratches could be residual grit in the cylinder from the polishing operation. IOMS has inspected fuel injector cylinders to determine whether our inspection technology could detect such scratches. Results for an acceptable and defective fuel injector are shown below.

Figure 1. Inside surface of cylindrical fuel injector with acceptable surface finish


Figure 2. Defective fuel injector surface showing scratches caused by polishing grit

Some fuel injector designs have been proposed with conical injector surfaces and spherical tips on the fuel lines that make contact with the injector surfaces. It is believed that this design will provide a better seal. IOMS can inspect the conical and spherical components of this design with modified probes that could detect defects large enough to permit fuel to leak out of an injector.