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Determination of appropriate leak tightness specifications for production leak testing of fuel system components has challenged the automotive industry for many years. This process has become more complicated as hydrocarbon emission regulations have been lowered (US-EPA, CARB LEVII, Euro5, etc.). Application of the equivalent channel (EC) concept can significantly simplify the process of determining leak tightness specifications. This paper describes the test procedure and results of a hydrocarbon emission study designed to define a critical geometry (known as Equivalent Channel-EC) that will plug after exposure to gasoline, resulting in no HC emission due to leaks during Vehicle SHED (Sealed Housing for Evaporative Determination) tests. This critical geometry will stop any measurable hydrocarbon leakage after enough time has elapsed for the channel to plug. Micro-channels of several diameters and lengths were tested in a Micro-SHED at 40 degrees Celsius for 24 hours.

A common problem encountered when designing a new product for demanding environmental conditions is specifying its leak tightness and measuring its seal integrity. Correlating empirical test data to production leak testing is an on-going challenge and a major source of confusion. Products of interest are those in automotive fuel and vapor management systems, A/C and cooling systems and power-train components and systems. A simple solution to the problem is proposed in this paper, based on defining the maximum acceptable microchannel geometry called the Equivalent Micro Geometry (EMG). Various mechanisms of fluid transport through microchannels are summarized. Flow through two types of EMGs, sharp edged orifices and microchannels, are examined. A practical implementation of the EMG approach to determine leak tightness specifications of components, exposed to automatic transmission fluid, is presented.