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 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.

Study on an injection quantity sensor. I: Evaluation of the integration procedure

“…In order to obtain the reliable integration of the ceramic sensor chip into the finished fuel nozzles, withstanding injection pressures up to 135 MPa (1350 bar), an integration procedure was developed, using technologies such as electro-discharge machining (EDM) and electron beam welding (EBW) with optimized parameters. The evaluation of the miniaturized mass flow sensor at pulse drives between 0.3 ms and 1.5 ms up to injection pressures of 135 MPa is reported in the accompanying paper [9].…”

LTCC: a fascinating technology platform for miniaturized devices

“…The sensor fabrication and the corresponding integration process into the nozzle are described in detail elsewhere [14][15][16]. Basically, the device consists of a metallic thin film element on a pressure-stable LTCC substrate with integrated electrical feed-throughs.…”

“…12: Transient characteristics of the drive pulse, the calculated injection rate, the injection quantity sensor and the IAI set-up at p i = 135 MPa and t dp = 0.3 ms. In [16], this point was interpreted as marking the end of the injection pulse and labelled with u b,max . This assumption is now verified by the hydraulic simulations.…”

Evaluation of electron beam welding technique for the integration of robust sensor elements into high-pressure automotive systems

“…To optimize the performance in respect to injection timings and fuel quantities the integration of miniaturized sensor elements is desired for monitoring the hydraulic status in each injector. For overload detection and for the closed-loop control of the overall system pressure the implementation of a pressure sensitive element into the common rail is state-of-the art (Robert Bosch GmbH 2006). Due to its location in the hydraulic system, however, it is impossible to measure very precisely small fuel quantities in the range of 1 mm 3 for each individual injector needed in the pre-and post-injection regime for a smooth combustion process and for reduced emission levels.…”

“…Different adapters for hydraulic and electrical purposes are attached, such as for feeding the diesel fuel to the nozzle tip, for re-cycling any leakage and governing fuel quantities to the tank and for supplying the drive pulse to the solenoid. Further details referring to the operation principle of such hydraulic valves for automotive applications can be found elsewhere (Robert Bosch GmbH 2006;Boehmer and Hummel 1997). Figure 2 shows the interior of a real nozzle of VCO class in an optical micrograph.…”