A Thermal Flow Sensor For Common Rail Injection Systems

We have developed a micromachined mass flow sensor placed on a high pressure stable substrate to measure on board the different injection quantities needed in modern direct injection (DI) systems for optimum performance. To detect the injection end/begin as well as the injection rate as precise and fast as possible, a flow sensor is for the first time completely integrated into the nozzle body very close to the injection holes. The thermal measurement principle is chosen, as gasoline and diesel fuel quantities can be detected and therefore, the use of this present flow sensor is not restricted to one of these different types of combustion engines. In this paper, we report about the fabrication process of the first prototypes, the dynamic characterization of the thin Molybdenum (Mo) films on the glass ceramic substrate by electrical square-wave testing and the first flow measurements at 200 bar carried out at a high pressure hydraulic test bench.