For 'on board' diagnosis purposes of the injected fuel quantity, ceramic flow sensor chips with a diameter of 2.2 mm were integrated into finished Common Rail injection nozzles of the valve covered orifice (VCO) or mini-sac hole (MSH) class. The influence of this integration step on the hydraulic performance of the high-precision injector nozzles which led to an optimized process flow with a minimized disturbance of the fluidic properties was investigated. Electron-discharge machining and electron-beam welding technology proved to be the key technologies for this integration process, providing a reliable solution for injection pressures ranging up to 135 MPa (1350 bar). With a highpressure hydraulic test bench the decrease in the injected fuel quantity as a function of welding parameters was determined for both nozzle classes. The geometrical distortion of the nozzle was mainly attributed to a radial bending of the nozzle tip and is dominated by the heat concentration during the welding process. In comparison, the integration of the ceramic sensor chip causes lower distortion values. By reducing the thermal energy input during welding a negligible influence of the complete integration process with respect to the hydraulic performance of original orifices is demonstrated at MSH injection nozzles.

For further optimization of the combustion process, the information about the actually injected fuel quantity is desirable, especially in diesel engines equipped with direct injection technology. A miniaturized hot-film anemometer with a titanium/platinum metallization on a lowtemperature co-fired ceramics substrate was developed and integrated into a Common Rail injection nozzle. The micro-flow sensor proved its high performance and its capability over the complete fuel quantity map of a high pressure hydraulic injection system where drive pulses for the operation of the injector range between 0.3 ms and 1.5 ms at injection pressures up to 135 MPa (1350 bar). In correspondence with measurements of an injection amount indicator integrated into the hydraulic test bench, the injected fuel quantity and the opening behaviour of the orifice were derived from the sensor signals as a function of injection parameters. Assuming a power law dependence on the fluid velocity for the flow-sensitive portion of the heat-transfer coefficient, a value of 0.5 for the exponent was determined experimentally, in excellent agreement with theoretical predictions.