On the second day of May 9, all parts of northern China have adapted to the rhythm of "freezing through the heart", from Heilongjiang, Inner Mongolia, Gansu to Xinjiang, from east to west, from the lowest temperature in several provinces and autonomous regions ranging from -13 °C to -40 °C.
"Old drivers" know that driving in the cold winter should properly "warm up" the vehicle or start the vehicle at a low speed to ensure the normal operation of the engine. After hundreds of years of development, fuel vehicles have a wide range of temperature adaptation and relatively good low temperature performance. For hydrogen fuel cell vehicles, the realization of non-destructive start vehicles in a low temperature environment has become a complete technical threshold, and it is also one of the main factors affecting the commercialization of fuel cell vehicles.
Low temperature cold start means that the fuel cell vehicle can successfully start at a temperature below 0 °C and can quickly increase the internal temperature of the fuel cell to 70 ~ 80 °C to meet the performance of normal operation.
Within a fuel cell system, hydrogen enters the hydrogen electrode (i.e., anode), and under the action of an anode catalyst, electrons are released to form positively charged hydrogen ions, which pass through the proton exchange membrane (PEM) to the cathode. At the cathode, the catalyst combines hydrogen ions with oxygen in the air to form water.
How fuel cell systems work (Image source: Network)
Once the temperature falls below the freezing point, the water will freeze - this means that the reactor, the core component of the fuel cell system, will freeze directly, and once the catalyst and proton exchange membrane on the stack membrane electrode are covered with ice, the start-up reaction performance of the fuel cell will be directly affected. If the freezing situation is serious, the fuel cell will even be completely unable to react and cause irreparable damage to the membrane electrode.
Whether the matching of the stack and each component of the fuel cell system can meet the requirements of low temperature start speed and engine output characteristics, in addition to the low temperature operation performance of each component itself, it also requires a fine control strategy.
With the design of wide-temperature stacks and low-temperature start control technology, Remodeling Technology has gradually overcome a series of challenges such as improving the ice capacity of low-temperature lower membrane electrodes, reducing the cooling chamber volume and the overall heat capacity of the stack, and improving the drainage capacity of the stack during cold start, shortening the purging time. The company's fuel cell system has passed the test of alpine harsh environment at -30 °C and nearly 1,000 meters above sea level, which confirms the system-level control strategy, the excellent level of materials and processes of the stack, and the high reliability design method of the fuel cell system of commercial vehicles.
On October 21, 2020, 15 10.5-meter hydrogen-fueled buses equipped with the remodeling technology fuel cell system were put into operation under the temperature conditions of nearly -30 °C in Baicheng, Jilin Province, becoming the first batch of mass-produced fuel cell buses operating in an ultra-low temperature environment in China.
Put into operation since 2020, the White City fuel cell bus has withstood the test of starting as usual in the extreme cold state of minus 30 °C
From a global perspective, the cold start technology of hydrogen fuel cells has been highly valued by academia, governments and industries. In North America, Europe and Asia, governments have successively developed corresponding national and industry standards in the past decade.
Taking the United States as an example, as early as 2005, the U.S. Department of Energy (DOE) formulated the first low-temperature cold start target for vehicle fuel cells, that is, to achieve a cold start within 30 seconds and -20 °C in 2010, and reached 90% of the rated power 1. After several revisions, the U.S. Department of Energy requires fast start-up within 30 seconds and -20°C by 2020 to add a functional requirement of -30°C no auxiliary start and -40°C assisted start2.
Based on policy regulations, industry development, etc., the world's major hydrogen fuel cell technology suppliers and automobile companies have conducted in-depth exploration and research on cold start technology for a long time in the past, and have made great progress, such as buses equipped with Ballard fuel cell systems can run smoothly in the extremely cold climate of many cities in Northern Europe, creating an excellent case of -30 °C cold start; Toyota Motor announced its hydrogen fuel cell vehicle "Mirai" at -18 ° in 2017 C's outstanding performance at launch 3; Hyundai conducted winter tests of NEXO's fuel cell electric vehicle in the northern Swedish town of Arjeplog in 2018. Thanks to energy-efficient heating and ventilation technology, the NEXO's fuel cell system, the Kona stack, achieves a cold start of -29°C4.
NEXO conducts winter tests (Image: Hyundai Motor)
On September 16, 2020, China's Ministry of Finance, the Ministry of Industry and Information Technology, the Ministry of Science and Technology, the National Development and Reform Commission and the National Energy Administration announced the Notice on The Demonstration Application of Fuel Cell Vehicles, and clarified the cold start of -30°C as one of the hard thresholds and key indicators of fuel cell system technology in the "Demonstration Objectives and Integral Evaluation System of Fuel Cell Vehicle Urban Agglomerations"5.
In the past few years, the engineer team of The Remodeling Technology R&D Center has carried out a series of forward development of low temperature cold start from the perspective of meeting customer needs and practical application scenarios, proposed many innovative solutions through continuous verification, and actively explored cold start application strategies. In the test data again and again, new cold start schemes are analyzed and summarized, and the cold start performance is continuously optimized. At the same time, the R&D team also needs to consider how to ensure the performance of the stack and minimize low temperature damage.
Fuel cell vehicles equipped with a remodeled technology fuel cell system have passed the test of alpine harsh environment of about -30 degrees Celsius and nearly 1,000 meters above sea level
"To put it simply, the core of low temperature cold start is to maximize the thermal efficiency of the stack at low temperature by changing the reactor operation point, so as to achieve the purpose of rapid heating across the freezing point." The person in charge of the cold start project of Remodeling Technology said, "The essence of the success of low temperature start is to ensure that before the stack temperature rises from minus zero to 0 °C, the residual water ice of the cathodic catalytic layer and the ice of the water production during the start-up process will not completely block the gas channel, so that the reaction can continue until the stack completes the ice." ”
The R&D team members of Reshaping Technology conducted multiple stages of research on cold-start technology with rigorous and efficient and step-by-step R&D work, and initially determined through experiments that -15°C~-20°C has been able to meet most of the application scenarios of hydrogen fuel cell vehicles, and then first carried out cold-start stack design and functional development under -15°C conditions. Subsequently, on this basis, through different wide-temperature temperature stack design schemes and low-temperature start-up control strategies, the state from start-up to half-load (that is, 50% of the rated power) is completed within 30 °C under -30 °C conditions.
Successfully completed more than 1,000 times of low-temperature start-up tests, low-temperature non-destructive cold-start technology for alpine environment is currently an important cornerstone to support the long-term life of the remodeling technology fuel cell system, and has also achieved the achievement of remodeling technology and Shanghai Jiao Tong University, Tongji University, Yutong Bus, FAW Group, Dongfeng Motor 5 units jointly completed the "long-life commercial vehicle fuel cell system key technology and industrialization" project, and won the first prize of the "China Automotive Industry Science and Technology Award" in 2020.
Reshaping technology believes that every small step forward of science and technology is stimulating the huge potential of hydrogen energy, transforming the hydrogen energy resources that the earth gives to mankind to take the least, transforming them into the driving force of hydrogen electric travel, and into the daily life of people. With its tireless pursuit of scientific and technological innovation, deep ploughing, international leading technology, continuous investment in research and development and core independent intellectual property rights, Reshaping Technology won the honorary title of the sixth batch of manufacturing single champions of the Ministry of Industry and Information Technology as the only enterprise in the hydrogen fuel cell industry in 2021.
Remarks: Reference documents/materials
1.https://www.hydrogen.energy.gov/pdfs/progress05/vii_h_9_pesaran.pdf
2.https://www.energy.gov/eere/fuelcells/doe-technical-targets-fuel-cell-systems-and-stacks-transportation-applications
3.https://publications.anl.gov/anlpubs/2018/06/144774.pdf
4.https://www.hyundai.news/eu/models/electrified/nexo/press-kit/all-new-hyundai-nexo-driving-performance.html
5.http://www.gov.cn/zhengce/zhengceku/2020-10/22/content_5553246.htm