Compared with gasoline, natural gas burns cleaner and more efficiently, produces about 25% less carbon dioxide, and lowers the cost of refining and processing. Therefore, natural gas-powered vehicles are attracting more and more attention. However, due to the high combustion temperature of natural gas, the requirements for metal engine components are much higher.

According to foreign media reports, researchers at the University of Virginia have developed a new type of high-temperature and low-cost alloy by combining nickel powder and graphene flakes, and applied for a patent. This new type of metal matrix composite material can maintain integrity at 1,000 degrees Celsius, or it will become a good choice for natural gas engine materials.

Such lightweight materials are called "graphene superalloy" (graphene superalloy). Because of the use of lightweight graphene materials, it is lighter than other nickel superalloys, but it is stronger and more durable than other metal mixtures. Chris Li, a professor in the School of Mechanical and Aerospace Engineering who led the research, said: "This material is very light and combines strength and toughness perfectly. It may become an ideal material for key components of natural gas engines such as fuel nozzles."

Superalloys have extremely important applications in many fields. They are also essential for new and renewable energy technologies, such as biomass "green" energy, biomass gasification, carbon capture and storage, bioenergy, concentrated solar energy, and solids. Oxide fuel cell, etc. They also play a great role in many other important technical fields such as jet engines, petrochemicals and materials processing. At high temperatures, the alloy will react violently with its environment, causing the material to fail due to corrosion. In order to prevent corrosion, a protective layer of aluminum oxide or chromium oxide is usually plated on the surface of the superalloy. This protective layer plays a decisive role in preventing metal corrosion. Researchers from Chalmers University of Technology in Sweden have done a systematic study on superalloys, explained the principle of the formation of superalloy protective layers and the reasons for their corrosion resistance, and proposed new methods for improving the properties of the alloys.

The researchers first explained two classic problems in the field of superalloys. The influence of the "active elements" (usually yttrium and zirconium) commonly present in superalloys; on the role of water vapor in corrosion protection. The researchers demonstrated the connection between these two factors and demonstrated how the active elements in the alloy promote the growth of the aluminum oxide protective layer. It is the presence of these active elements that cause the in-growth of the aluminum oxide protective layer , Thereby promoting the transfer of water vapor from the surrounding environment to the alloy substrate. The interaction between active elements and water promotes the formation of metastable "messy" nano alumina layer.

Researchers draw inspiration from nature when designing materials, such as mother-of-pearl shells. "They have a layer after layer of structure." Mother-of-pearl is composed of hexagonal aragonite flakes, and its strength and toughness are extremely rare in engineering materials. In the manufacture of most composite materials, the combination of two alloys will cause most composite materials to lose ductility or toughness. However, with a structure similar to aragonite, the strength of graphene and nickel composites can be increased by 73%, and the tensile capacity is only reduced by 28%. This composite material can even maintain high hardness at a high temperature of 1000 degrees Celsius.

Replacing battery and engine materials with graphene-enhanced materials can help reduce energy consumption. The challenge to achieve this goal is that the cost of graphene can be as high as hundreds of dollars per gram. Lead researcher Zhang said: "When it is applied to vehicles, cost needs to be considered. Cost is always the first. If the cost of graphene cannot be reduced, it will not be possible to apply graphene in large quantities in automobiles."

Researchers predict that in the next five years or so, natural gas engines may be widely used, especially for commercial trucks. Trucking companies are looking for ways to reduce fuel costs and carbon emissions. Currently, the US Department of Energy and Transportation is supporting research on innovative materials to adapt to alternative fuels and reduce costs and greenhouse gas emissions. On a smaller, lower-cost scale, graphene can be used to improve common technologies. For example, it can be used to make flexible screens, or even flexible batteries for mobile phones, or for 3D printing.

The ability of air supply protection continues to increase

The high gas price and the lack of gas can increase, which is the most worrying problem for drivers. "This problem mainly occurs in the winter heating season in the northern market. Residents use a large amount of gas for heating, which can reach 2-3 times the average daily gas consumption. Insufficient capacity of urban peak shaving and gas storage facilities will inevitably cause problems." Experts from China Society of Automotive Engineers Li Yongchang said that my country has increased the construction of underground gas storage. In 2018, my country’s comprehensive gas storage capacity has increased to 16 billion cubic meters, and 27 gas storages have been built. With the establishment of the national official website company, LNG receiving station storage With the enhancement of the gas capacity, the gas supply situation in the northern winter will be improved year by year.

"CNOOC has the ability to promise to guarantee the supply of LNG required for'green transportation' under any circumstances." Jin Shuping, deputy general manager of China Offshore Oil & Gas Group, said that CNOOC made three major promises of "guaranteed supply, quality, and price." ——In other words, to ensure the supply of LNG resources at the filling point of vehicles and ships, guarantee high-quality customer service, and ensure that the price is competitive, CNOOC has implemented a price linkage mechanism between vehicle and ship LNG and No. 0 diesel to ensure that the price is always lower than the national standard No. 0 diesel, and enhance the availability of LNG vehicles. Economy.

Good policy for development

It is reported that as of the end of 2018, the number of natural gas vehicles in my country was 6.7 million, of which the number of LNG vehicles was 440,000; the number of gas stations was 9,000; it ranked first in the world for four consecutive years. Many experts at the meeting said that the situation will continue to improve.

Starting from July 1 this year, key regions, the Pearl River Delta region, and the Chengdu-Chongqing region will implement the National VI emission standards in advance in accordance with the requirements of the "Three-year Action Plan for Winning the Blue Sky Defense War" and promote the use of gas vehicles that meet the National VI emission standards. The "Diesel Truck Pollution Control Action Plan" jointly issued by the Ministry of Ecology and Environment and other 11 departments also proposes that before the end of 2020, the Beijing-Tianjin-Hebei and surrounding areas, and the Fenwei Plain will speed up the phase-out of National III and below emission standards to operate diesel trucks with 1 million diesel trucks. Vehicles. In addition to national policies, various local governments have successively introduced measures to restrict diesel vehicles and scrap subsidies. For example, Tianjin Port, Weifang Port, and Yantai Port banned the entry of coal and diesel vehicles into the port; 3. Diesel vehicle scrapping subsidy policy, giving scrapping subsidies ranging from 10,000 to 100,000.

Statistics show that my country currently has 63.263 million vehicles below the national level. This means that a large number of unqualified vehicles need to be updated in the short term, and some vehicles will be replaced with natural gas vehicles. According to relevant sources, the price of diesel has continued to rise, and the price of LNG has fluctuated and declined as a whole. The sales of LNG heavy trucks in the first quarter of this year are gratifying. Li Yongchang, a distinguished expert of the Chinese Society of Automotive Engineering, said that in the context of favorable policies, a prosperous sales market for LNG heavy trucks this year and next is a high probability event.

Performance issues restrict industry development

"Natural gas vehicles are developing rapidly, but they are still in a low-level expansion stage." Hong Ju, leader of the single-fuel compressed natural gas vehicle research group of the Peasant-Industrial Democratic Party, pointed out that the performance of natural gas vehicles in my country is poor.

It is understood that natural gas passenger cars are mainly modified cars for a long time, and a large number of medium and small natural gas cars are modified cars of gasoline cars-dual-fuel cars, that is, the original gasoline cars are partially modified, the engine is not changed, only the installation The natural gas storage system, the ignition device and the switching of the two fuels will change the fuel due to the lack of targeted technical measures, resulting in unstable emissions. When using natural gas, the power performance will be reduced by about 10-15%. Consumption will also increase by about 5%.

The combustion temperature of natural gas engines is higher than that of gasoline and diesel engines with the same emissions, which easily causes nitrogen oxidation in the cylinder. If special combustion treatment technologies and devices are not used, a certain amount of nitrogen oxides will inevitably be emitted in the exhaust gas. With the tightening of vehicle exhaust emission standards, the control of nitrogen oxide emissions has become an important task in the technological transformation of natural gas vehicles.

"As long as targeted measures are taken, the National VI emission requirements can be met." Hong Ju said that my country has successfully developed a three-way catalytic device for natural gas vehicles, which has achieved certain results in improving emissions. Some automobile OEMs have also made changes to the newly manufactured dual-fuel automobile engines, with improvements in performance and emissions.

Link to this article： The development of lightweight high-temperature alloys will help promote natural gas vehicles

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