NREL researchers have achieved this breakthrough, of great significance to the heavy-duty transportation and fuel cell electric vehicle (FCEV) industries, using the state-of-the-art capabilities offered by NREL in its Energy Systems Integration Facility.
For more than a decade, NREL has supported cutting-edge research on hydrogen fueling practices for light-duty FCEVs. However, HD trucks and machinery are a target of an entirely different scale. "Designing and building these systems, the first of their kind, is a major technical achievement," said project manager Shaun Onorato. "This research is fundamental to characterizing high-definition hydrogen refueling and opens the door to new protocols that will shape the future of decarbonized transportation."
Much less refueling time and more charging
The IHS project addresses research challenges and technology gaps in the development of high-flow hydrogen fueling systems, including certain semi-trailers and marine, rail and mining applications.
The project is funded, in part, by DOE's Office of Hydrogen and Fuel Cell Technologies and ultimately aims to compete with conventional diesel vehicle refueling times (about 10 minutes), resulting in an ambitious hydrogen gas mass flow rate of 10 kg/min on average (20 kg/min peak) based on a maximum on-vehicle storage potential of 100 kg h2. This rate is approximately 10 times the average mass flow rate currently used for lightweight FCEVs.
On April 26, the IHS team exceeded this target, demonstrating an average mass flow rate of 14 kg/min (21 kg/min peak) with a filling of 40.3 kg in a bank of 8 hydrogen storage tanks - similar to those used by HD vehicles - in 2.87 minutes. The Laboratory states that "this intermediate milestone will pave the way for the project to reach the final milestone of completing a 60-80 kg fill in less than 10 minutes".
New Hydrogen Generator
As for the design of the new hydrogen generator, the researchers first turned to NREL's Hydrogen Filling Simulation Model (H2FillS). H2FillS is a fast, flexible, and free thermodynamic model that simulates hydrogen supply from a hydrogen station to a light FCEV.
In 2021, the research team already achieved substantial improvements in the H2FillS model to adapt it to the requirements of the EH and the IHS project. The latest version optimized the computational speed of the model so that it is now 20 to 40 times faster than the previous version and added optimization of the pressure ramp rate parameter. In addition, H2FillS is currently exploring the entire hydrogen fueling process to calculate the optimal fueling rate for high-end vehicles.
Another area of focus has been the temperature distribution inside vehicle hydrogen storage tanks, as this is essential for the development of new refueling protocols. Specifically, the researchers carried out 3D computational fluid dynamic modeling using NREL's Eagle supercomputer to locate potential hot spots and optimize mixing characteristics.
Throughout the project, the team completed numerous full and partial fills with computational fluid dynamics models to explore aspects such as the effect of tank size, injector diameter and injector angle on the gas mixture. They then balanced these results with experimental tests to continually validate their process and further improve the H2FillS for HD applications.