An accelerated comparative exhaust system cycling durability test has been developed at the Ford Motor Company Research and Engineering Center Dynamometer facility. This paper is a summary of events leading up to the development of the test, a description of the test procedures and conditions, the equipment, the actual test results and usage of the test.
The initial design of an exhaust manifold for a new four cylinder engine successfully passed a rather long thermal cycling test program on an engine dynamometer, a test traditionally used in design verification. However, vehicle test results proved unacceptable and necessitated an immediate redesign of the exhaust manifold. Time constraints required a rapid comparative test to evaluate this redesign. Simply modifying the test parameters of the existing thermal cycling test procedure proved inadequate. It was necessary to combine periodic physical loading of the outlet system with thermal cycling to produce the desired results.
Time limitations, equipment availability and economic considerations eliminated a “state of the art” approach to this problem. A more practical method was derived. System loading was accomplished by mounting the test engine on soft vehicle engine mounts and allowing the engine to rock during periodic changes in the engine RPM. The test room exhaust orifice plate and flex hosing [approximately 10.4 Kg (23 lb.)] were mounted on the vehicle exhaust manifold header pipe and partially supported by a spring. During engine rock, the weight would load the exhaust manifold header which, in turn, would load the exhaust manifold. The springs were used to prevent undesirable impact loading of the system.
In an effort to evaluate this mechanical loading, a triaxial accelerometer was mounted on the exhaust manifold for comparative purposes. Five different mounting configurations of the engine were tested for severity and the most severe was used on the test cycle (Appendix A).
The consistent results of the accelerated durability test supports the continued use of mechanical loading and thermal cycling in comparing exhaust system components and revealing system weaknesses and potential failure modes.