In August 2022, the Journal Automotive Engineering (Vol. 44) published a research paper Design, analysis and validation of distributed drive and liquid hydrogen-powered heavy duty commercial fuel cell vehicles. Authored by IHFCA Chairman Ouyang Minggao and his team at Tsinghua University, Bu Yu at the Beijing Institute of Aerospace Testing Technology, and Wang Lijun and Qin Zhidong at Foton Motor, the paper proposes a new technical solution for liquid hydrogen (LH2) commercial fuel cell vehicles (FCVs), featuring a distributed drive system designed for urban heavy-duty (HD) and long-haul freight transport.
The paper explores the design and development of high-power fuel cell systems, on-board LH2 storage tanks, boil-off gas (BOG) treatment, and safety monitoring system. It also introduces the design, integration, manufacturing and testing of a Foton 35-ton (35T) LH2 fuel cell truck and a Foton 49T LH2 fuel cell tractor in a real road environment. In addition, the paper discusses the use of high-performance in-wheel motors to achieve an overall transmission efficiency of 91%.
The key parameters of the Foton 49T LH2 fuel cell tractor listed in the research paper are summarized below and compared with those of Daimler GenH2 truck. (Note: the source of the Daimler GenH2 data is from an EU hydrogen conference in 2021 and is not from the Tsinghua research paper)
A. The design of powertrain and distributed drive system
The paper analyzes the efficiency of a distributed electric drive system, which has an almost 10% improvement in transmission efficiency over a traditional centralized drive system, as shown in Figure 1 below. Based on electric wheels and the overall consideration of loads, performance and manufacturing, the research team developed a twin in-wheel motor electric drive solution, as shown in Photo 1.
The power system developed by the research team has the following advantages:
Energy efficient drive: a distributed electric drive system maximizes drive efficiency;
High efficiency of fuel cells: A hybrid power system decouples the power output of the fuel cell system from the power demand of the vehicle, allowing the fuel cell system to operate stably at high efficiency;
High power performance: a power battery system able to provide instantaneous high power output and quick response to vehicle power needs. To save space on the chassis layout, a power battery with a relatively small capacity (<100 kW·h) and a high peak power (>500 kW) is used;
Efficient thermal management: the LH2 system not only improves hydrogen storage density, but also absorbs excess heat generated by the fuel cell system during the LH2 evaporation process.
B. Advanced fuel cell systems
In 2019, the Tsinghua research team developed China's first 100 kW-level fuel cell system, which was listed by the Ministry of Industry and Information Technology. The system, with a rated power of 109 kW, was equipped with an air compressor that matched its power capacity, a hydrogen recirculation pump, and a cooling-water pump. In 2021, the Tsinghua team built a single-stack fuel cell system with a rated power of 240kW, system efficiency of over 60%, and durability of more than 20,000 hours.
The Tsinghua team’s first generation fuel cell system features an optimized stack design and control strategy, with 109 kW output at an operating temperature of 75°C, hydrogen pressure of 170 kPa (absolute) and air pressure of 150 kPa (absolute). The system has been installed on fuel cell buses and has undergone 1,500 hours of on-road testing, with an estimated system durability of over 10,000 hours.
C. On-board LH2 storage system
LH2 is an extension of LNG technology. Since 2016, China has developed advanced on-board liquefied natural gas (LNG) storage technology for automotive applications. With a whole domestic supply chain, the cost of a typical LNG cylinder in China has fallen below RMB 30,000.
Based on existing LNG technology, the research team has developed a high-capacity on-board LH2 storage solution, which is expected to have a hydrogen storage cost as low as RMB 1,000/kg once a domestic supply chain is fully established. This represents a significant advantage over Type IV 35MPa and 70MPa cylinders, as shown in Table 3.
Editor’s note: China has the world’s largest LNG market in the automotive sector. According to Sublime China Information (SCI), by end-2018 there were 343,933 LNG-fueled vehicles on the roads in China, including 236,265 LNG heavy-duty trucks and 107,668 LNG buses and coaches.
After extensive research on adiabatic design, vacuum system, supporting structure, and lightweight design, the Tsinghua research team and the Beijing Institute of Aerospace Testing Technology developed an LH2 storage system with an optimized structure, enhanced safety and a tank storage density of over 10wt%. The research also included the design of a boil-off gas (BOG) re-liquefaction system to maintain stable pressure in the LH2 storage tank.
The LH2 storage system of the Foton 35T truck (shown in Photo 5 in Section D) includes two identical LH2 tanks (shown in Photo 3), each with a capacity of 30 kg. The Foton 49T tractor (shown in Photo 6 in Section D) includes two different-sized tanks: a small one on the side with a capacity of 30 kg and LH2 storage density (excluding accessories) of 9.33wt%, and a larger one (shown in Photo 4) at the rear with a capacity of 80 kg and LH2 storage density (excluding accessories) of 10.24wt%.
Editor’s note: The Beijing Institute of Aerospace Testing Technology has developed on-board LH2 storage tanks in three sizes: 30 kg, 60 kg, and 80 kg, for MD/HD truck applications. The Institute has made key technology breakthroughs in the overall design and structure of LH2 cylinders, LH2 storage and supply systems and parameters, and the integration of aerospace LH2 technology with FCV technology.
D. On-road vehicle testing and validation
Based on the structure in Figure 2 below, the Tsinghua team developed a chassis and powertrain arrangement for the Foton 35T truck (shown in Photo 5) and Foton 49T tractor (shown in Photo 6). Both vehicles have undergone real-world road testing, and the test results are listed in Table 4.
In summary, the research reported in the paper has successfully validated several innovative technologies for distributed drive LH2 heavy-duty commercial FCVs, but more time is needed to optimize and iterate the technology into a market-ready product. The research paper also includes a discussion of potential bottlenecks and challenges for the technology's applications.
The current cost of LH2 for end-user applications is very high, but it could potentially be reduced to below RMB 30/kg through two approaches: decreasing the cost of renewable energies and making technological breakthroughs in large-scale LH2 plants.
Based on current solar electricity cost at RMB 0.2/kW·h and an energy consumption of 8 kW·h/kg in an LH2 plant (with a capacity of 30 tons/day), the production costs of LH2 could be controlled below RMB 15/kg. In addition, the transportation and refilling costs of LH2 are significantly lower than those of compressed gaseous hydrogen (CGH2), making it more likely that the end-user price of LH2 will decrease to below RMB 30/kg.
The durability and system cost of high-power fuel cells for commercial FCVs must meet the requirements of 30,000 hours and RMB 50,000, respectively. According to China's Hydrogen Fuel Cell Vehicle Roadmap 2.0 (2020-2035), the cost of fuel cell systems in China is projected to decrease to RMB 1,000/kW by 2030, which means RMB 100,000-200,000 for a 100-200 kW fuel cell system used for HD commercial FCVs.
The current fuel cell system cost for commercial FCVs is too high, at around RMB 5,000/kW. In comparison, the cost of internal combustion engines is about RMB 50,000. Therefore, subsidies or supporting policies may be necessary to bring the long-term cost of fuel cell systems down to below 300 RMB/kW after subsidies.
It is important to note that fuel cell efficiency is also crucial, as fuel costs are a key factor in the economics of HD commercial vehicles. Therefore, when the market penetration of fuel cells reaches a tipping point, it may be feasible to increase fuel cell prices in order to improve fuel cell efficiency and durability, leading to a lower overall life cycle cost.
Liquid hydrogen (LH2) storage tanks have only been used in certain industries, with almost no application in automobiles. Therefore, comprehensive testing and system development are necessary to enable a large-scale adoption of LH2 in the automotive industry.
To provide context, China built its domestic LNG supply chain during the 13th Five-Year Plan (2016-2020) to gradually replace imported components such as valves, pumps and dispensers, resulting in a rapid price drop for LNG tanks to below RMB 30,000. China has also developed a two-tank LNG system for long-haul heavy-duty vehicles with a range of 1,000 km. Based on China's success with LNG vehicles, it is optimistic to predict that similar breakthroughs could be made in the LH2 industrial chain.
The trend in commercial vehicles is towards intelligence and electrification, with increasing requirements for electric drive systems. However, current centralized drive configurations are unable to simultaneously meet efficiency requirements at both high and low speeds, which often leads to the use of transmission structures such as gearboxes. This results in a complex system that is difficult to achieve an overall efficiency of 90%.
On the other hand, the potential of in-wheel motor drive technology in terms of economic benefits and braking performance has not yet been fully developed, although its advantages are already clear, as seen in recent products released in China and abroad. However, the main challenges facing this promising technology are cost and engineering reliability.
Please click here to download the full journal paper in Chinese.