Study on an injection quantity sensor. II: Evaluation of the sensing element

Abstract

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 low-temperature 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.