Analysis of out-of-spec events during refueling of on-board hydrogen tanks

For refueling on-board hydrogen tanks, table-based or formula based protocols are commonly used. These protocols are designed to achieve a tank filling close to 100% SOC (State of Charge) in s safe way: without surpassing temperature (-40°C to 85°C) and pressure limits (125% Nominal Working Pressure, NWP). The ambient temperature, the initial pressure and the volume category of the (compressed hydrogen storage system, CHSS are used as inputs to determine the final target pressure and the pressure ramp rate (which controls the filling duration). However, abnormal out-of-spec events (e.g. misinformation of storage system status and characteristics of the storage tanks) may occur and result in a refueling in which the safety boundaries are surpassed. In the present article, the possible out of specification (out-of-spec) events in a refueling station have been analyzed. The associated hazards when refueling on-board hydrogen tanks have been studied. Experimental results of out-of-spec event tests performed on a type 3 tank are presented. The results show that on the type 3 tank, the safety temperature limit of 85°C was only surpassed under a combination of events; e.g. an unnoticed stop of the cooling of the gas combined with a wrong input of ambient temperature at a very warm environment. On the other hand, under certain events (e.g. cooling the gas below the target temperature) and in particular under cold environmental conditions, the 100% SOC limit established in the fuelling protocols has been surpassed.