Optimal Safe Fueling of Hydrogen Powered Industrial Trucks

Hydrogen fuel cell powered electric trucks are widely used in industry where more than 20000 systems are currently installed, achieving more than 100 million operating hours. The electric trucks are equipped with fuel cell power systems which incorporate a permanently mounted Hydrogen (H2) tank containing compressed hydrogen gas and enabling onboard fueling. The H2 tanks vary in capacity, ranging from 20 to 150 liters and are made of either steel (4130) or composite material (aluminum liner with carbon fiber overwrap). Fueling can be performed several times a day depending on the usage of the electric truck. It is critical to develop optimal fueling designs in order to minimize the fueling time and maximize operator productivity without exceeding the maximum allowable temperature of the H2 tank. A dynamic model was developed which included transient heat convection, conduction and fluid flow to predict the temperature change of the gas in the fueled tank using a finite difference approach. The input variables include ambient temperature, supply temperature, supply pressure, initial tank temperature, specific tank qualities (tank geometry and material properties), and Dispenser orifice size. The output variables of the code include the fueling time, fill ratio, the pressure and mass of the supply reservoir and fueled tank vs. time and the temperature of the H2 inside the fueled tank and the temperature distribution through the tank wall thickness vs. time during the fueling process. The fill ratio is defined as the final mass in the tank over the max allowed mass in the tank defined by the governing standard (SAE J2601-3). The model was validated using experimental data of various H2 tanks. The model was used to determine optimal orifice size for fleets of different H2 tank sizes and types. A multi-orifice design was also developed which optimized the fueling process.