Characterization of diesel injectors using piezoresistive sensors

A slender piezoresistive sensor was described which can measure the extreme 3D surface topography of microscale mechanical parts. Non-destructive quality testing of, e.g., high aspect-ratio micro holes is insufficient since suitable sensors are not available. As a consequence more than 50 million fuel injectors are shipped every year but the spray holes which determine through their geometry both efficiency and exhaust emission of combustion engines are not fully tested. Recently, we described a piezoresistive cantilever as the only sensor so far for measuring form and roughness directly inside injector nozzle holes. Based on our initial design sensors are now available from a pilot production using a silicon wafer scale process. They show much improved performance (vertical/lateral resolution, speed, noise, light sensitivity) enabling us for the first time to perform a comprehensive study with the actual generations of state-of-the art injector nozzles as well as prototype holes.