Individual Testing Technology For Car Fuel Tanks

Deeply hidden and mostly unnoticed, fuel tanks have their existence. They are an important safety feature in automobiles, which are subject to ever greater technical requirements today. In addition, lawmakers regularly tighten emissions standards for cars, which increases the requirements for the entire fuel supply. A central starting point for optimizations are the tanks - for vehicles in the mass market and also for racing cars. Porsche is using special pressure tanks in its current 918 Spyder hybrid sports car for the first time. To test the operating loads of these new types of fuel tanks, the Fraunhofer Institute for Durability and System Reliability LBF examined the tanks under cyclical internal pressure.Due to the considerable volume of 87 liters and the low test pressures, the institute expanded its test facilities and developed a new test concept that was successfully used in the course of the validation of pressure tanks.

Simulate environmental influences

For the fatigue tests, the researchers at Fraunhofer LBF developed a highly flexible test concept, which on the one hand is very variable in the volumes to be examined, regardless of the filling medium. On the other hand, test pressures of up to ± 500 hectopascals can be set relative to the ambient pressure and thus both positive and negative pressures can be generated. By connecting external climatic chambers to the test room, additional environmental influences, such as temperature, can be simulated in order to individually map the range of uses of the tank.

Because of the often complex installation situation of fuel tanks and for the most realistic test possible, the isolated test chamber has a volume of two cubic meters. "With this test facility, which is specifically geared to customer needs, the Fraunhofer LBF can accompany the design process of manufacturers in parallel with tests, and the knowledge gained can flow directly into numerical design approaches," explains Daniel Hofferberth, responsible for the new test concept at Fraunhofer LBF. Where test volumes in the range of a few milliliters at pressures of up to 500 bar were previously possible, the institute now has a new application area with pressures of up to ± 500 hectopascals for large-volume components thanks to the new test facility.

Assemblies can also be checked

In the test environment, both individual components and larger components combined to form an assembly can be examined cyclically with a superimposed temperature profile with automated pressure testing and level monitoring. Part of the test is also the monitoring of highly stressed areas using strain gauges. Local stresses can thus be measured and a possible failure can be detected.

The Fraunhofer LBF carried out the operational load test on the pressure tanks on the basis of the test specification provided by Porsche AG under room temperature and elevated temperature under cyclical internal pressure in an original monocoque from the manufacturer. Stefan Rieser, Development of Whole Vehicle Material Technology at Porsche, is delighted with the test technology that was specially implemented at the Fraunhofer LBF. “The fuel tank in the Porsche 918 Spyder was validated successfully. In addition, the knowledge gained from the test bench test can be transferred to other vehicle models and can thus shorten the development time.”(Jv)