On Board Injection Rate Measurements at DI-Systems With a Micromachined Mass Flow Sensor

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 fast and precisely 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 both 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, the fabrication process of the first prototypes is reported mainly focusing on the technology for the LTC (Low Temperature Cofired) ceramics. Additionally, FEM simulations on the velocity profile in the injection nozzle are performed to calculate in a further step the power consumption P_elec of the thin film resistor during operation at different overheat ratios. Finally, the first injection rate measurements up to 60 MPa are presented, discussed and compared to signals gained from an injection amount indicator integrated in the high pressure hydraulic test bench.