Abstract
Injection systems of modern commercial vehicle power units are still a frequent topic for development engineers in terms of durability and reliability. Therefore, the content of this study is just an investigation of the dynamic behaviour of high-pressure injection pipes of a four-cylinder combustion engine. The modal properties of the injection tubes are evaluated by experimental modal analysis (EMA). Another phase of the measurements is the sensing and analysing of the acceleration on each injection pipe during the engine speed ramp in the entire range of the speed spectrum. There was investigated the modal behaviour of the structure to the operational character of the excitation. The work includes a numerical model established by finite element method (FEM), where the boundary conditions correspond to the real installation of injection pipes from the measurement. The modal properties of injection pipes were primarily investigated through the numerical approach, several variants of pipe attachments were considered in simulations. Comparing the FEM results of different pipe attachments, the suitability of the clamp position with respect to the specific installation in the power unit from the measurement is discussed. From the evaluated results, it is possible to assume the dynamic behaviour of the high-pressure injection pipe in the power unit. Based on the performed analyses, the critical mode shapes of the injection pipes are described considering the engine operating condition. When the engine speed frequency and some pipe eigen frequency interfere together, it is undesirable state. In many cases, this leads to a crack initiation and subsequent damage of the injection pipes during the cyclic load. The presented results and conclusions in this study should improve the overall knowledge on high-pressure fuel pipes in terms of modal properties and its vibration behaviour during operating condition.
Highlights
In the last decade, diesel fuel injection systems have undergone considerable progress
It is clear from the results, when the assembling the injection pipes without clamping elements, the excitation frequency interferes with the first natural frequency of the injection pipe leading to fourth engine cylinder
The modal properties diagnostics is essential in terms of reliability and fatigue life of high-pressure fuel pipes
Summary
Diesel fuel injection systems have undergone considerable progress. The authors of this study declare that so called integrated process design, which includes the heading and autofrettage process, significantly increases the fatigue life of the neck part of the injection pipes These are confirmed by performed fatigue tests results and according to the investigated structures by using scanning electron microscope technology. Some deviations occur in mode frequencies, when the fuel weight is or is not considered in numeric simulation This numerical modelling differences have greater impact mainly in lower eigen frequencies of fuel injection pipes, which are influenced most by operating engine speed. These form the connection between the injection pump and the injector of a four-cylinder diesel engine. This study brings more complex overview about high-pressure injection pipes in terms of modal properties, pipe clamping optimization and its dynamic behaviour under the operating engine conditions
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