Abstract
Keywords - Diesel Injection, Injection Characteristic, Injection Measurement, New Measuring System, Correction of Measured Signal
The timing of fuel injection in diesel engines fundamentally affects their combustion process and thus fuel consumption and noise and exhaust emissions. This paper presents the results of a method for measuring the injection characteristic of a state-of-the-art high-pressure diesel fuel injection system, which was developed at the Institute of Mobile Systems at Otto von Guericke University Magdeburg. The experimental method is supported and verified by extensive, detailed simulated tests with 1D-CFD-code AMESim.
Now as before, the injection characteristic cannot be measured directly in an engine. Available measuring instruments measure the injection characteristic from outside an engine and have not yet been verified with a so-called master device (lab device). Hence, a lab device was developed, which generates a defined, precisely measurable "injection characteristic" that serves as the input signal for downstream injection characteristic measuring instruments. Both simulated and experimental tests have verified that piston movement in the measuring cylinder generates a determinable injection characteristic (fuel flow resembling injection) in the lab device. An inductive displacement sensor detects piston movement and the thusly generated injection characteristic is calculated from the product of piston movement and the cross-sectional area of the piston. This quantity of fuel can be delivered to the injection characteristic measuring instrument directly connected with the lab device. This facilitates a comparison of the input signal (injection characteristic measured with the lab device) and output signal (injection characteristic measured with a conventional measuring instrument). This comparison can not only be used to calculate the tolerances but also correction factors for commercially available measuring instruments.
It is essential to understand the physical processes in the fluid in conventional measuring instruments during injection. This entails analyzing the influence of the highly dynamic process of injection into the fluid during which pressure waves form and the medium develops resistance. This resistance can be responsible for errors in conventional measuring systems. That is why 1D-CFD-code AMESim is employed to mechanically simulate this effect in every operating point. The influence of the resistance can be inversely calculated from the simulation, thus making it possible to mathematically correct the measurement results of conventional measuring systems without any simulation.