Mahle’s Hydrogen Focus Spans Fuel Cells, ICEs
Advanced Engineering director Dr. Marco Warth details Mahle’s HFC technologies and how challenges are being met.
Hydrogen fuel cell (HFC) technology is gaining momentum in the mobility sector, with substantial volume expected by 2025 to 2030, according to Dr. Marco Warth, director of corporate advanced engineering mechatronics at Mahle. The iconic cylinder-systems supplier for diesel and gasoline engines is now a major player in the industry’s investigation of hydrogen as a future transport fuel. Dr. Warth sees the company’s work as laying a cornerstone on which rests CO2-neutral mobility.
Having established a broad spectrum of products for fuel cell systems, Mahle is monitoring potential hydrogen applications for combustion engines. An R&D project that could be beneficial to both is a carbon-fiber gaseous hydrogen tank with a plastic liner that would increase hydrogen storage density and save production costs. Mahle CEO and chairman Dr. Jörg Stratmann stated that much work still needs to be done to industrialize HFC technology consistently. He sees it also complementing the internal combustion engine, hence the company’s wider view of hydrogen application.
The Stuttgart, Germany-based company announced in September 2020 an agreement to work with Canadian fuel cell manufacturer Ballard Power Systems to develop and industrialize HFCs for commercial vehicles for North American, European and Asian markets. It recently joined the Hydrogen Council, a worldwide initiative of leading energy, transport and industrial companies, all believers in the fuel’s potential. The company will be a member of working groups tackling issues of hydrogen/fuel cell usage and complementary infrastructure suitable for all HFC vehicle types.
Mahle has established a close relationship with Phoenix, Arizona-based Nikola, developer of HFC- and electric-powered trucks. It is supplying the vehicles’ entire cooling and air-conditioning systems. As part of its R&D program, Mahle has revealed what it describes as its “Competence Center” for mechatronics at Kornwestheim, near Stuttgart. And at Fellbach, it has commissioned an all-new test facility for electric drives. An e-mobility development center is nearing completion in China.
Common system, standards needed
To make HFC trucks and passenger vehicles a cost-effective, high-volume alternative to battery propulsion for Europe, governments and industry have to resolve “the chicken-and-egg problem” related to refueling infrastructure, Warth said. HFC technology will become commercially attractive for trucks first, according to Mahle, so it is increasing its investment there. He added that to enable trucks to operate on hydrogen, only a small number of fueling stations along main corridors across the EU are needed.
Part of the funding available through the EU’s “Next Generation” program for “green” investments should be devoted to building up the “backbone” of a hydrogen fueling infrastructure, Warth asserted. He said Mahle believes there will be one common system in Europe for both commercial vehicles and cars, as many synergies exist between the segments. But there is a need for standards for hydrogen refueling. “The EU has to act quickly to allow for key industry partners like Mahle to develop appropriate equipment such as hydrogen storage tanks,” Warth said. “We believe gaseous hydrogen storage has many advantages over liquid hydrogen for both cars and commercial vehicles, so this should become the new standard,” he said.
There is also the issue of “green” hydrogen, generated from renewable sources. “The EU’s ‘Hydrogen Strategy’ is a step in the right direction, committing the bloc to have at least 40 GW of renewable hydrogen electrolyzers by 2030, producing up to 10 million tons of renewable hydrogen,” he said. “Another 40 GW of renewable hydrogen should be imported from EU neighboring countries.” To realize these goals requires “the right framework conditions at a national and European level” including “a more ambitious” Renewable Energy Directive (RED) than the current target rate of 14%, which has not been adapted to the new climate goals of the EU Commission.
“To achieve this, we are calling for at least 23% renewable fuels and a minimum quota of 5% hydrogen and e-fuels in the RED by 2030,” Warth said. He believes that HFC vehicle applications, particularly in the commercial sector, are “likely to reach a substantial volume by the second half of this decade.” From 2030 onward, volumes in the EU will continue to increase “given the commitment from the Paris Climate Agreement to be CO2 neutral by 2050.”
Unique FC engineering
The air management within fuel cells places extremely high demands on the components used. To prevent damage to the cell, harmful gases such as SO2, O3, NOx and NH3 as well as particulates, need to be separated reliably. For this purpose, Mahle has developed a multilayer filter medium that Warth describes as “highly effective.” In this design, a substrate material ensures mechanical stability, a particulate filter layer removes NaCl, a molecular layer prevents NH3 from entering the fuel cell, an activated carbon layer absorbs unwanted hydrocarbons, and an additional, specially impregnated activated carbon layer adsorbs SO2, H2S and NOx.
There is also the critical issue of managing humidity. “The water balance of a polymer electrolyte fuel cell significantly affects efficiency and service life,” Warth explained. “If the membrane dries out, this will lead to a gas breakthrough, while surplus water has the undesired effect of blocking the gases to freely enter the fuel cell. Therefore, it’s not sufficient to filter the external air supplied to the fuel cell – its humidity must also be precisely controlled.”
For this purpose, Mahle – together with affiliated partners and with funding from the German Federal Ministry of Economics and Technology – has developed a flat membrane humidifier to ensure that the supplied air is humidified reliably. In this device the exhaust and supply air are in cross flow and separated by the membranes. A moisture exchange takes place across the membrane material. Deionized coolant is used to cool the fuel cell; it is not electrically conductive and thus will not cause short-circuit current flow in the fuel cell.
As a result, the components used in the coolant circuit must be resistant to ionized water. Mahle has developed a special process that ensures component durability. To ensure the non-conductivity of the coolant, the company has further developed an ionic exchanger already in field use in multiple applications, Warth said.
Highly efficient cooling is essential for HFCs, creating packaging challenges as systems’ complexity increases. Larger coolant coolers are a result of the need for separate circuits for the cell stack, the battery/electronics and the electric motor, as well as the overall increase in waste heat and the reduced temperature levels in comparison with the combustion engine.
“A higher volume of coolant is required in order to compensate for the lower temperature differential between the coolant and ambient temperatures,” Warth explained. “Fuel cell stacks require continuous monitoring during running operation. This prevents damage and also means that crucial input variables, such as gas or air supply, can be controlled.”
The Mahle Fuel Cell Monitor Module has two microprocessors that process the signals from the stack and provide feedback to the central control unit, he noted. When required, the voltage in the fuel cell stack can be discharged directly via a semiconductor module. To ensure trouble-free operation, the power distributor and discharge resistor should be housed on a cooling plate, he advised.