The increasing request of vehicles fuelled by Compressed Natural
Gas (CNG) requires that the safety issues related to this kind of
fuel should be analyzed more and more thoroughly. So far, the
minimum requirement for a CNG tank is to set up a Pressure Relief
Device (PRD) triggered by temperature.
This work aims to develop a procedure able to perform thoroughly
tank behavior analyses, in presence of fire, in order to reduce the
number of expensive experimental tests and to improve the design
criteria of tank safety devices. The procedure consists in the
solution of the unsteady solid-fluid conjugate heat transfer
problem, by means of numerical simulations, in order to evaluate
the transient behavior of both the temperature field inside the
solid walls of the tank and the thermo-fluid-dynamic field of the
compressed gas inside it, when it is exposed to a heating source.
Moreover, the melting process of the fusible plug, inside the PRD,
is simulated. In order to validate this procedure, experimental
tests have been carried out on a suitable test rig.
Several heating conditions, even unlikely, but able to
jeopardize safety, have been considered. The condition
characterized by a flame located on the opposite side of the PRD
has been recognized to be the most critical with respect to
explosion risk. In this case, the relationship between time and
tank pressure has been numerically evaluated. The fusible plug,
inside the PRD, has been checked to be completely melted of the
fusible plug before the pressure reaches the safety limit.