Model-based analysis of the system reliability under accelerated life tests for the fuel supply of an oil burner
For the assessment of reliability of technical products, time consuming endurance tests are used with and without accelerated life testings. In the accelerated life testings, a stress factor is imposed to reduce the failure time of the component. The stress factor can be an increased utilization rate or increased operating temperature. The diversity and complexity of liquid fuels for vehicles and domestic oil heaters has increased recently due to the use of biogenic components. The topic of fuel stability and aging is the subject of current research. At OWI Science for Fuels gGmbH, test methods for application-related examinations were developed for this purpose. The test time could be reduced significantly by the imprint of physical stress. A research question that had only been investigated secondarily was the relationship between the quality characteristics of the fuel-carrying components, the aging of fuel and components, and the failure behavior. The question is taken up in this work. The objective of this work is to describe a model-based method for the analysis and simulation of aging processes in technical systems.
In particular, the interaction of fuel aging, component aging and quality characteristics of the fuel-carrying components is investigated. By means of a model-based approach, the influence of physical stress on the acceleration of the experiment is analyzed and the admissibility of the test acceleration is verified.In this thesis a numerical simulation model of the oil burner application is modeled, and the failure behavior of an accelerated life test is analyzed by stochastic simulation. The quality properties of the components, aging of the components and fuel aging are considered by means of a kinetic approach to the oxidation stability of the fuel. In the investigation, the tank volume is initially reduced from 60 to 20 liters and the impact on failure behavior is analyzed. The results show the impact of components behavior on system failure behavior. In particular, the influence of component quality characteristics on failure behavior is analyzed. The functional relationship between the reduction of the tank volume as a physical stress factor and an acceleration factor is presented. The investigations with the validated system models have shown that the reduction of the tank volume from 60 to 20 liters is a suitable stress factor. Since there is no change in the property of the distribution function during the acceleration of the experiment, the tank volume reduction is shown to be a suitable stress factor. The reduction of the tank volume from 60 to 20 liters led to an 82 percent acceleration of the test. Due to the functional description of the stress factor and acceleration factor, the result of the simplified test bench experiment can also be transferred to real applications. Thus, with a tank volume of around 1000 liters under otherwise identical conditions, a mean time to failure of around 3700 hours can be expected.