I. International development trend and development status of gas engine With the rapid development of the world economy, the rapid increase in car ownership, the car has brought great convenience to people, has made great contributions to the development of human society, but at the same time it consumes large amounts of petroleum resources, emits a large number of harmful gases, and It poses greater damage to the human living environment and becomes the main source of pollution for urban pollution. To solve this problem, people have been seeking to change the energy structure and adopt low-nuisance vehicles alternative fuels. Some large international automobile companies have successively developed electric vehicles, alcohol vehicles, and natural gas vehicles. Judging from factors such as technological maturity, economic efficiency, availability, and resources, natural gas vehicles are superior to electric vehicles and alcohol vehicles. Therefore, in recent years, the total vehicle ownership in the world exceeds 750 million vehicles, of which natural gas vehicles have more than 6 million vehicles, and more than 6,000 gas stations are located, mainly in rich gas-lean countries such as Italy, New Zealand, Argentina, and Indonesia. And the United States, Japan, etc. with strict environmental protection laws and regulations. Internationally renowned companies such as Dai-Ke, Cummins, Iveco and others are all making every effort to develop and promote their own natural gas engines. It is worth mentioning that the United States is in the leading position in LNG vehicle technology. From the point of view of promoting vehicles, LNG is not only suitable for urban buses, but also for taxis and large freight vehicles, especially long-distance vehicles. From the trend of the United States and Europe, the focus of the development of natural gas vehicles in various countries has shifted from CNGV vehicles to LNGV. The number of gas vehicles in China currently exceeds 220,000. There are more than 712 refueling stations in 19 key promotion and application cities (regions). The main reasons for the rapid development of natural gas vehicles are: 1. The need for environmental protection Natural gas vehicles are clean fuel vehicles with low exhaust emissions and less environmental pollution. Compared with gasoline vehicles and diesel vehicles, emissions are reduced as follows: In the United States, natural gas has become a widely used substitute fuel for automobiles in order to meet the Clean Air Act Amendment (CAAA) 1990 standards. There are 31 states in the U.S. that have made mandatory use of natural gas vehicles. The State of New York has established a six-year plan for the application of clean fuel vehicles, and plans to reach 80% of gas vehicles by 1996; Texas State stipulates that by September 1994, 50% of school buses, 15% of buses, and government agencies Must have dual fuel capabilities. 2. Natural gas automotive technology is maturing The development of natural gas vehicles has had a history of more than 70 years since the 1930s. In particular, after the development in recent years, the technology has matured. The advanced electronic technologies and machinery manufacturing technologies have made natural gas vehicles safe and controllable. It is guaranteed that the driving range will be increased from the initial 50 to 70 kilometers to more than 300-400 kilometers; the weight of natural gas vehicle cylinders and the volume of filling stations will be greatly reduced; it is as convenient as filling gasoline with gasoline, and rapid inflation is only required. 2 to 5 minutes. 3. Natural gas vehicle infrastructure gradually complete With the development of natural gas vehicles, natural gas vehicle filling stations are gradually forming a network. It is estimated that there are more than 6000 gas filling stations in the world. 4. Security and economy Compared with gasoline, diesel and other alternative fuels, the use of natural gas vehicles is generally 50% lower than the price of gasoline. Natural gas is a light gas with a high ignition point and is less dangerous than gasoline under normal temperature and pressure. Natural gas vehicles have good cold start performance, stable operation, low maintenance cost (about 50% of conventional fuel vehicles), and direct use of methane as fuel, which can not only greatly reduce the wear and tear of automobile mechanical friction, extend the service life, but also make the operation simple and convenient. It is also 40% lower than a fuel car. Long engine life. 5. The government formulates preferential policies To protect the environment and reduce pollution, many governments have formulated a series of encouraging policies to promote the development of gas vehicles. Such as natural gas price concessions, natural gas vehicles, lower taxes and fees, production of fuel supply equipment and construction of gas stations, etc., are given preferential policies in terms of capital and taxation. Second, the development status of China's gas engine At present, foreign CNG engines have been widely used in third-generation technologies. The more advanced LNG direct-injection technology has been used in a small number of trials. Its power, economy, and emissions are excellent, but its development is difficult and expensive. The cost is also high and domestic development has not yet begun. The first generation of products is mechanical, the second generation is simple closed-loop control, and the third generation is electronically controlled injection CNG technology. Electronically controlled CNG injection system uses high-pressure injection, through the throttle sensor, gas flow sensor, speed sensor, water temperature sensor, intake temperature sensor, pressure sensor and oxygen sensor through the central processing unit to control the ignition, air-fuel ratio. The development of gas vehicles in China began in the 1950s, namely low-pressure natural gas vehicles. The development and application of natural gas vehicles in the mid to late 1980s was accelerated. Domestic large-scale automobile plants and engine factories such as Dongfeng, Jiefang, Shangchai, Weichai, and Yuchai have continuously increased their product development efforts, and have successively introduced their respective products for promotion and application in the market. The main products are divided into single natural gas fuel vehicles and dual-fuel vehicles. (natural gas/gasoline or diesel). According to the different forms of natural gas used by gas vehicles, it can be divided into: compressed natural gas (CNG), the main component is methane, the pressure is generally in the range of 20-30 MPa; liquefied natural gas (LNG) and natural gas are under ultra-low temperature (-162°C) at atmospheric pressure. After liquefaction, the natural gas is compressed and heated by the purification process, and the heat is removed by cooling under the action of the mixed refrigerants N2, C1, C2, C3, and C4, and then throttling and expansion to obtain liquid natural gas. Under the normal atmospheric pressure, the volume is approximately It is 1/625 of the same amount of gaseous natural gas, natural gas after liquefaction is 1/625 of the standard volume, insulation container pressure is 0.05-0.5MPa, sulfur, mercury and other impurities are almost completely removed in the liquefaction process of LNG. Both types of fuel engines have been used in the country. 1. Compressed natural gas vehicles In 1988, China imported new facilities for CNG refueling stations, modified automobile parts and high-pressure gas cylinders from New Zealand, Australia, Canada and other countries. Stations were established in Nanchong, Daqing and other places. At the same time, localization of filling station facilities and car modification parts was carried out. At present, people in the industry have generally recognized the advantages of using a single CNG as a fuel. The major domestic engine manufacturers are developing third-generation natural gas engines and are continuously replacing mechanical engines with lower technological levels. CNG has been promoted in Sichuan, Chongqing, Beijing, Xi'an, Inner Mongolia, and other places. 2. Liquefied natural gas vehicles are a new type of environmental protection car that has only begun to develop in recent years after CNG cars and LPG cars. Naturally, they are also natural gas vehicles. However, LNG carried by cars has higher fuel density and pressure than CNG. Low, required fuel tanks are light in weight, and the mileage (300 to 800 km) of a car's primary inflation is far greater than that of CNG. LNG can be transported like oil at the same time. It also has the advantages of CNG and LPG, and overcomes their shortcomings. Therefore, it has stronger practicability, and due to the adjustment of China's energy strategy structure, there will be more LNG resources imported into China for use in the future, and it is considered to be the development direction of gas vehicles in the future. The LNG refueling system currently being implemented in China includes the Beijing LNG demonstration refueling station. A total of 11 bus demonstration vehicles are in operation; the project of the Urumqi Single Fuel LNG Bus Demonstration Project has 20 single fuel LNG bus demonstration vehicles in operation; Changsha The project of single fuel LNG bus demonstration project in the city has 52 single-fuel LNG bus demonstration vehicles in operation, and the operation conditions are normal. Third, China's natural gas vehicle engine development prospects 1. Natural gas vehicles are of great significance to reducing automobile exhaust pollution and saving petroleum resources At present, large and medium-sized cities are seriously polluted by the automobile exhaust, causing serious disasters to people's lives. Taking the environment of a certain city as an example, the current automobile ownership is only over 1 million vehicles. The air pollution level is equivalent to that of a foreign automobile city of 4 million. The nitrogen oxides in the urban area have exceeded the national standards for many years, and the traffic trunks are exceeding the standard. serious. To this end, the government’s relevant departments, some universities, and research institutes are paying more and more attention to the development, promotion, and application of natural gas vehicles. The national industrial policy also encourages the development of energy-saving and low-pollution products. From November 1996, the National Automotive Standardization Technical Committee established a natural gas vehicle working group to set up a standard system for natural gas vehicles in China. In September 1997, the State Bureau of Technical Supervision approved the establishment of a natural gas and liquefied petroleum gas vehicle standardization subcommittee to make natural gas in China. The standardization work of automobiles has been fully carried out. 2. China's natural gas and liquefied petroleum gas resources are relatively abundant and have the basic conditions for the development of natural gas vehicles. China's natural gas reserves are relatively optimistic. According to the survey, China's natural gas resources are about 38 trillion m3, and proven reserves are 1.8 trillion m3, which is 5% of the total resources and can be harvested for about 300 years. In 2005, China's natural gas production was 30 billion m3. Except for chemical raw materials and civilian fuels, there was still surplus (about 20%), of which some natural gas was wasted (about 1 billion m3). According to estimates by experts, the gas consumption of 100,000 natural gas vehicles is about 1.5 billion m3, which is only 7.5% of current natural gas production. 3, gas vehicles use low cost, easy to be accepted by users The more economical use cost is the favorable condition for the promotion of natural gas vehicles. Compared with the current prices of gasoline, diesel and natural gas in our country, comprehensive consideration is given to factors such as engine service life, maintenance costs, and engine oil costs. Natural gas vehicles have significant economic benefits. Fourth, domestic and foreign natural gas engine product technology Natural gas engines mainly use the following technologies: Most of the development is based on diesel engines, and only a small portion based on gasoline engines. This is mainly due to the ability to use the diesel engine's mature technologies for supercharged intercooling. Many natural gas engines that use lean burn technology and which are theoretically more fuel-efficient than combustion also account for a certain percentage. Natural in-cylinder injection technology. Natural gas engine closed-loop electronic control technology. Natural gas components development reliability technology. Such as pistons, valves, valve seats, nozzles and so on. 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