61 Hydrogen fuel cells | Deep insight By forming the membrane from a liquid material and applying the catalyst at the same time, the base film was no longer required, and the membrane thickness was reduced by 40%, compared with that of the previous systems, cutting costs. Durability was improved by increasing the use of cerium and neutralising side reactants from water electrolysis, which is one of the causes of deterioration of the electrolyte membrane. All this results in fuel cells with 15% fewer layers without lowering net output. The output per individual cell was increased by optimising the area of the cell’s power-generation section, and the power consumption of the supporting equipment, the BoP, was also cut. The structure of the electric turbo air compressor was simplified from the previous two-stage compression to one-stage compression by increasing the compressor’s rotation speed by 1.5 times. The humidifier bypass valve was eliminated as the stack became capable of operating at high humidity and the EGR pump was eliminated through the adoption of a new control technology. When the ambient temperature is low, the water-cooled intercooler warms up the intake air to reduce the amount of water (dew) from the condensation that forms at the inlet of the stack and improves low-temperature start-up performance down to -30 C. The hydrogen pump was eliminated as the pressure-boost control during startup improved hydrogen-displacement performance. The temperature and water-level sensors were replaced with temperature prediction and water estimation, based on data from other sensors. The pressure-switching valve and secondary regulator were removed by using a chamber and optimising the injector-mounting structure. Humidity was another area that Honda focused on. The electrolyte membrane that lets hydrogen ions pass through to the air electrode side has the characteristic that a rise in humidity increases its permeability to boost power-generation efficiency. However, if water remains on the power-generation surface, it narrows the airflow path and reduces power-generation efficiency. To maintain the appropriate humidity, it is therefore necessary to adjust the temperature of the cell and carefully control the amount of evaporation of the surrounding water. The new system estimates the amount of water vapour in the ambient air supplied to the fuel cell using a modelbased estimation method, and it realises optimal humidity control based on that model using an electric temperaturecontrol valve and a high-efficiency humidifier. This enables more precise control, lowering the stack temperature to boost humidity and increasing the temperature to lower humidity. Such precise control enables the system to stabilise the stack’s power generation and boosts durability by preventing the deterioration of the cell by increasing the level of humidification. The operational Honda Class 8 truck concept is powered by three of the new Honda fuel-cell systems, each at 80 kW. These fuel cells are in mass production at Fuel Cell System Manufacturing, a jointventure facility with GM in Brownstown, Michigan. The 240 kW fuel-cell system can provide a top speed of 70 mph and a driving range of 400 miles with a highpressure, 700 bar tank that holds 82 kg of hydrogen, as well as a 120 kWh battery. Ballard Power Systems has developed its ninth-generation fuel-cell engine, aimed at heavy-duty applications, such as trucks and construction equipment. The FCmove-XD engine has a volumetric power density of 0.36 kW/L and a gravimetric power density of 0.48 kW/kg. The scalable, single-stack, 120 kW fuel-cell engine integrates the power controller with the DC/DC converter, air-compressor inverter and power-distribution unit, along with proprietary software controls. This integration is part of a focus on cutting the number of components by 30% to reduce size and boost reliability. The design allows up to three modules to operate as one system with a single interface, capable of delivering a power output of 360 kW. The engine has a design life of 30,000-plus hours of operation or over one million miles in truck operation at typical duty cycles. “The power and performance requirements of the highly segmented truck market are particularly demanding due to various use cases, including high vehicle utilisation rates and payload requirements,” says Silvano Pozzi, vice-president of Product Line Management. “One of the compelling features of FCmove-XD is scalability, based on modularity. We can offer customers efficient integration of 120 kW, 240 kW and 360 kW solutions, dependent on truck class, use case and duty cycle. “For example, two engines, totalling 240 kW of power output, can be easily installed in the engine E-Mobility Engineering | July/August 2024 One fuel-cell module for a Class 8 truck (Image courtesy of Honda)
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