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Abstract
This article introduces briefly the R&D status of natural gas powered
auto vehicles and governments'measures promoting the development of natural gas powered vehicles in foreign countries and the R&D status of natural gas powered vehicles in China. The article also introduces what have been doing in Xi'an in this regard over the past few years and the relevant advantages in this municipality. It is pointed out that the development of natural gas powered vehicles are, on the basis of the present technological level, an effective alternative for a simultaneous solution of energy structure readjustment and reduction of environmental pollution. The article also proposes relevant countermeasures and suggestions.

1 Significance of Developing Natural Gas Powered Auto Vehicles
The present world annual auto vehicle production has reached 50 million, with the amount of registered auto vehicles of nearly 700 million. It is estimated that by 2030, the world's registered auto vehicles will be as many as 1 billion. In China, annual auto vehicle production has reached 1.45 million with the total amount of registered auto vehicles of 12.70 million. Estimates also show that the number of registered auto vehicles will increase to 20 million by the year 2000. On the other hand, China has become a petrol oil net importer. During 1994 ～ 1996, China imported an annual amount of 15 million tons of oil products. In 1997, China imported a total of 11.00 million tons of oil products and 3.00 million tons of crude oil.Now,  let's look at another aspect of the development.Of the total of more than 640 cities in China, only less than 1% have their air quality up to the national class I standard. According to the results of the monitoring qdconducted by the WHO and the regularly publicized list of 10 big cities with the worst atmospheric pollution in the world, China's Shinnying, Beijing and Xi'an were listed in 1991. In 1995, Beijing and Shanghai still remained on the list.
At the present time, of various alternative energy sources developed for consumption by auto vehicles, natural gas is an outstanding one for it
can help reduce 25% of the CO₂ which would otherwise be discharged in the tail gas of the vehicles. Besides, natural gas can help reduce 80% of the CH₄ compounds emission, 70.5% of SO₂ emission in the tail gas , 99.99% of SO in the tail gas, 41.67% of particle pollutants, 52.8% of non-methane hydrocarbon, 89.73% of CO, 40% of noise and the emission of Pb eliminated. Results from experiments and tests show that environmental pollution can be alleviated to a large extent by using natural gas powered auto vehicles. In addition, natural gas powered auto vehicles also offer advantages of better safety and optimal economy. With lower prices of CNG compared with petrol and diesel presently in many countries, the operation costs of autovehicles powered by these fuels is only about 60% that of petrol. See Table 1 below for the comparison of the prices of petrol and other fuels:

2 The Development Status of Natural Gas Powered Vehicles in Some Foreign Countries
Proceeding from their own national interests in environmental protection, energy readjustment and cutting down on their excessive reliance upon oil, governments of many countries worked out many relevant measures and preferential policies covering pricing of natural gas for auto vehicles' use, taxation for natural gas powered vehicles and coordination between competent authorities. All these policies are designed aiming at encouraging and promoting the development of natural gas powered vehicles. Take the US as an example, the “Clean Air Act Amendment" (CAAA) was proposed in 1990. In order to fulfil the CAAA requirements, natural gas was selected as the most favored alternative fuel and provisions regarding a compulsory use of natural gas powered auto vehicles were promulgated in 31 states of the US in 1992, the “Energy Policy Regulations '92" was passed in the US and in 1993 the policy of tax abatement for natural gas was implemented. In January 1998, the US President presented an environmental protection plan with relevant expenditure of US 6.3 billion. The development of natural gas powered auto vehicles was included in that plan. It is the US that provided the most preferential policies for the development of CNG powered auto vehicles. Under these policies, CNG powered auto vehicle buyers will benefit from a tax abatement of US Dollar 3,000～4,000 which is corresponding to the total cost for retrofitting a dual fuel CNG powered auto vehicle in the US Statistics show that up to 1996, a total of more than 5 million natural gas powered auto vehicles were used in 43 countries. Of this grand total, more than 4 million are LPG powered vehicles and more than 1 million are CNG powered vehicles. The number of LNG powered auto vehicles, however, is still limited.

	USA	Canada	Italy	France	Swiss	Russia	Australia	Czech
Price of petrol(litre)	100	100	100	100	100	100	100	100
Price of diesel(litre)	94.0	78.2	57.5	59.3	61.1	77.2
Price of LPG(litre)	49.6	36.9	49.3	47.6	50.7	57.8
Price of CNG(m³)	38.8	23.6	44.0	42.5	46.3	35.7	30～50	below50

Comparison of petrol and LPG consumed by cars (Nanhai)			Comparison of petrol and CNGconsumed buses(Chengdu)
Fuel consum /100 km	Petrol 10 litres	LPG 12 litres	Fuel consum/100km	petrol 27.5 litre	CNG 30.2m³
Unit price (yuan/litre)	2.35	1.2	Unit price (yuan/litre or m³)	2.20	1.5
Total expense (yuan)	23.5	14.4	Total expense(yuan)	59.4	45.3

	Ignition point	Strength of gas cylinder(fuel tank)	Octane value	If antidetonant is added
petrol	400°C	Low	Catalyzed cracked petro l88 ～ 89	Yes
natural gas	700°C	Much stronger than petrol tank	120	No

Number of CNG powered auto vehicles in some countries						Number of LPG powered auto vehicles in some countries
Country	Number of vehicles	Number of gas stations	Country	Number of vehicles	Number or gas stations	Country	Number of vehicles	Number of gas stations	Country	Number of vehicles	Gas refilling station
CIS	380000	480	Canada	32000	180	US	1700000	1250	France	50000	1539
Russia	380000	480	Japan	15000	150	Italy	1100000	1550	New Zealand	40000	800
Italy	450000	480	Australia	400000	30	Holland	700000	1988	Spain	40000	350
New Zealand	380000	480	China	3000	48	Japan	300000	600	Canada	25000	250
USA	380000	480	Germany	1100	45	Mexico	75000	620	Algeria	20000	100
Argentina	380000	480	France	600	4

It can be seen from Table 4 that natural gas powered auto vehicles develop at a fast rate in some foreign countries as a result of the great attention and support given by the respective governments.

3.1 Domestic situation
Starting in the 1950s, China's first natural gas powered auto vehicles
used rubber bags for fuel gas storage and consumption at constant pressure. In the mid 1980s, China National Petroleum Oil & Natural Gas Corp. imported some foreign technologies and equipment and carried out trial operation of CNG powered vehicles. By the end of 1996, a total of 3030 natural gas powered vehicles were in service with their fuel gas supplied by 57 gas refilling facilities. For the use of gas fuel powered auto vehicles in different places in China, see Table 5 and 6.
Development of gas fuel powered auto vehicles started much later in comparison with that in some foreign countries. The technical level of the development in China is by no means very high but the development is pushing forward with great momentum.

	Sichuan Chongqing	Xinjiang Oil Field	Daqing	Shanghai	Urumuqi	Haikou	Harbin	Xi'an	Nanhai	Dagang
Number of CNG powered vehicle	2000	86	182
Number of LPG powered vehicles		521	35	Trial operation	Trial operation	Trial operation	Trial operation	6	Trial operation	2
Number of CNG stations	26	2	2
Number of LPG stations		5	3

Natural gas prices in four regions supplied by Beijing						Natural gas prices in Sichuan Province
Preferrential wholesale price	Sichuan 0.70 yuan	Chongqing 0.73 yuan	Zhongyuan 0.60 yuan (internal preferrential price)	North China 0.50 yuan	Beijing 0.99 yuan	gas for commercial consumption	Gas for industrial use	gas for fertilizer production	gas for household consumption
CNG selling price	Sichuan 1.20～1.30 yuan	Chongqing 1.30 yuan	Zhongyuan 1.50 yuan	North China 1.40 yuan	Beijing 1.80 yuan	1.03 yuan	0.733 yuan	in big plant: 0.62 yuan and 0.59 yuan for small plant	0.733 yuan

      The Shaanxi Provincial Party Committee, Provincial government, Xi'an Municipal Party Committee and Municipal government have been attaching great importance to the development of natural gas powered auto vehicles. In 1994, Xi'an Municipal Science and Technology Commission proposed, in the document entitled “The Feasibility Research Report on the Development of Natural Gas Powered Vehicle Industry in Xi'an",policies and measures designed for that very purpose.On the basis of appraisals and evaluations conducted by experts from competent fields, the Xi'an municipal Party Committee and municipal government made a decision to develop such industry in Xi'an, and this proposal was regarded as a significant measure of Xi'an municipality in terms of readjusting the local energy structure, improving the local environmental quality and cultivating new areas of economic growth. In order to win necessary support from the state government, Xi'an Municipal Planning Commission submitted to the State Planning Commission the project proposal regarding developing natural gas powered vehicles in Xi'an (also as the relevant feasibility report), with copies sent to the State Science and Technology Commission, State Economic and Trade Commission, Ministry of Machine Building Industry and China National Petroleum Oil and Natural Gas Corp. and some other competent authorities, expressing Xi'an's sincere hope to become the exclusive city for the development of natural gas powered auto vehicles in China. Then on January 16, 1998,Xi'an Municipal Government submitted another document to the State Science and Technology Commission, applying for becoming the only city for the development of natural gas powered vehicles on trial basis.
    For an effective leadership over the development of natural gas powered vehicles, the Xi'an Municipal Leadership Group for the Development of Natural Gas Powered Auto Vehicles (hereinafter referred to as the Leadership Group for short) was created by the Xi'an Municipal government in November, 1995. The Leadership Group was headed by a Vice Mayer, while the Director General of Xi'an Municipal Science and Technology Commission, Director General of the Municipal Planning Commission, Director General of the Municipal Economic and Trade Commission and 2 Vice Presidents of Xi'an Jiaotong University and     Xi'an Highway Jiaotong University act as the deputy heads of the Leadership Group. Some main leaders of Xi'an's governmental organs at the bureau's level act as members of the Leadership Group. With its offices arranged in the premises of the Municipal Science and Technology Commission, the Leadership Group's executive director is a deputy head of the Municipal Science and Technology Commission who is concurrently a member of the Leadership Group. A division head sent separately by the Municipal Planning Commission, Municipal Economic and Trade Commission and Municipal Public Works Bureau act as the deputy executive director of the Leadership Group. Decisions of the Leadership Group are implemented by the Executive Office who is also responsible for the coordination and treatment of the routine work of the Leadership Group.
      Over the past two years, the Leadership Group has been involved in research and decision-making process regarding the major policies and guidelines governing the development of natural gas powered auto vehicles in Xi'an. As a result, some preferential policies will become debut regarding the subsidies for natural gas price, tax exemption and tax abatement for the construction of natural gas refilling station for vehicles. The Leadership Group also worked out “Natural Gas Powered Auto Vehicles Development Plan during the Ninth Five-Year-Plan Period and Strategic Goals for 2010" and “Provisional Rules of Xi'an Municipal Government Regarding Spreading the Use of Natural Gas Powered Auto Vehicles". The Leadership Group also coordinated some very important activities involving tackling major technical problems for the purpose of realizing industrialized production of natural gas powered auto vehicles and the industrialization of technical achievements in this regard, and coordinated some very important affairs in the industrialization of natural gas powered vehicles in the city. On November 17, 1996, a common agreement was reached in the form of a minute of meeting by the Leadership Group and China Aerospace Industry Corp. regarding the development of natural gas powered auto vehicles in Xi'an. By now, the retrofitting project of a batch of 50 buses for the city's public transit carried out jointly by Xiangyang Aerospace Industrial Co. and Xi'an Municipality is nearly completed and the demonstration project of joint-construction of natural gas refilling stations has already been started. With all equipment for the gas refilling stations' use already arriving in Xi'an, the demonstration buses can be put into trial operation in August this year.
      Xi'an municipality's advantages in developing natural gas powered auto vehicles：
      1) Advantages in resources. With proven reserves of 280 billion m³ and predicted reserves of3,000 billion m³, the northern part of Shaanxi Province is endowed with the largest inland natural gas resources. The North Shaanxi Gas Field started to supply natural gas to Xi'an from June 29, 1997.According to the first phase of the national development plan, the
gas well pressure in Jingbian will be 4.5 MPa while the pressure at the
outlet in Xi'an will be 1.7 MPa. In normal case, an annual amount of 580
million m³ of natural gas can be supplied to Xi'an, Xianyang and Tongchuan, of which 367 million m³ of gas will be supplied to Xi'an. If the
gas well mouth pressure is raised to 5.8 MPa, a total of 750 million m³
of natural gas will be supplied to the said three cities annually. If pumping stations are set up in Yan'an or Huangling and the local gas pressure is raised from the original 4.5 MPa up to 5.8 MPa, an annual total of 1 billion m³ of natural gas will be supplied to the above mentioned three cities. So, with sufficient supply of natural gas, Xi'an can afford the development of natural gas powered auto vehicles. In addition, the quality of the natural gas supply is up to the overall quality requirements for class II gas in SY7514-88, qualified to be the substitute for petrol as fuel for auto vehicles.
    2) Technological advantages.
    (1) On the basis of a research report concerning the development of natural gas powered auto vehicles in Xi'an conducted several years ago, Xi'an Municipal government submitted a “Natural Gas Powered Auto Vehicles Project Proposal (also in the capacity of feasibility report)" to the competent authorities of the state government in 1995. By now, Xi'an further obtained a large amount of information and data including the state-of-the-art of gas powered vehicles in some foreign countries, technical levels in this regard both at home and abroad, some relevant relations, rules, specifications, standard, production techniques and even gas vehicle selling prices, etc. All these are of great value to the development of gas powered vehicles in Xi'an, stipulating local regulations and policies and working out local conditions based implementation schemes.
      (2) The Compressor Engineering Research Center of Xi'an Jiaotong University is the unique compressor engineering research center approved by the State Planning Commission with quite some famous compressor experts and scholars and well equipped experimental facilities and highly competent technical reserves. The Automobile Department (the former Department of Internal Combustion Engine Engineering) of the University also has a group of world famous experts and professors on the development of internal combustion engines. Most of them have the experiences in doing research work in the field of petrol engines and diesel engines that are designed for consuming CNG. The University's National Key Laboratory on Mechanical Structure Strength and Vibration and the Institute of Material Science & Engineering have quite some world famous experts and scholars whose main interests are in the field of compound material basic theoretical research, applied research and manufacturing. They have the capabilities to thoroughly solve both the theoretical and practical problems about pressurized compound material gas cylinders.
      (3) As a institution of higher learning with its main academic interests in the field of highway communications and transport, Xi'an Highway Jiaotong University has the Automobile Testing Technology Center of the Ministry of Communications, Auto Vehicles Energy Conservation Training Center of the Ministry of Communications and the Xi'an Automobile Products Quality Supervision and Inspection Center in its premises. With all these facilities, research experiments and performance testing can be conducted for the natural gas powered vehicles. The task force team of the University, headed by Professor Zhou Yun, Executive Director of Shaanxi Provincial Automobile Engineering Society, developed generating oven gas/diesel oil powered dual fuel auto vehicles in as early as in the 1950s. Again in the 1980s, the task force team developed methanol/diesel oil powered hybrid vehicles. Over the recent years, efforts were concentrated on the solution of petrol and LPG fuel application problems on the auto vehicles made in China. Based on the experiments, analysis and research on the imported LPG devices from Japan, Korea and Russia, the localized design has been finalized. Moreover, a matching research has been carried out on a imported Italian CNG device on a auto vehicle made in China and an alternation design scheme was proposed for the domestically manufactured engine and auto vehicle, thus laying a sound technical foundation for the starting-up of the natural gas powered auto vehicle industry.
    3) All-round matching advantages. As a locality with many universities, colleges and defense industries concentrated, Xi'an is endowed with many
highly experienced professionals in various specialties and advanced experimental facilities and industrial processing facilities. With the help of effective coordination, rationalized disposition of productive factors, it is without any saying that China's own high-tech product will surely be
developed on the basis of digesting, absorbing the foreign gas powered vehicle experiences without the need to put in too much investment for equipment. It is also possible to form China's own intellectual property right and relevant products in this way. At the same time, the defense industries such as No.11 Research Institute of Aerospace Industry Corp., the Northwest Photoelectric Instruments Co. of the Weaponry Industry Corp., the No.113 Factory of Aviation Industry Corp. are all endowed with large amount of advanced manufacturing equipment of various types, high level engineering professionals and well trained technician contingents as well as ready production factors such as workshops. Should natural gas powered vehicle retrofitting equipment and gas refilling station equipment industries be developed locally in Xi'an,a large amount of investment for fixed assets could be saved, thus greatly shortening the lead time for the making of the natural gas powered vehicle industry.
    4) Locality advantages. In the political report to the 15th National Congress of the Chinese Communist Party, Mr. Jiang Zemin, Secretary General
of the Chinese Communist Party Central Committee, pointed out: “Reforms,
opening to the outside world and economic development should be speeded up in the mid-western areas of China by bring into full play the resources
advantages and industrial advantages. The state government will surely intensify its support to the western part of China by giving priority to the infrastructure projects and resources development projects". These remarks are of great significance to speeding up the economic and social development in the mid-western part of China and minimizing the gap between the eastern and western parts of the country and it also brings about good opportunity to the economic take-up in Xi'an. With the presently registered auto vehicles amounting to 170,000, the natural gas powered auto vehicles will offer a good opportunity in gas as a substitute for petrol because of the huge market. In Xi'an area, highway system is so developed that to the north Yan'an, Yulin and Ningxia can be reached, then by way of Shenfu in Shaanxi Province and Inner Mongolia, Beijing can be reached. To the east, the national highway No.301 is stretching to Zhongyuan Oil Field and Shengli Oil Field and is leading to Gansu Province and Xinjiang Uygur Autonomous Region via Baoji to the west. To the south, the highway is coming into connection with the Chengdu to Chongqing Highway. The coming into being of the natural gas powered auto vehicle industry in Xi'an will surely contribute greatly to the readjustment of the local energy structure and controlling atmospheric pollution in the mid-western part of China.

4.1 Key technological problems to be tackled
      1) When auto vehicles use natural gas instead of petrol, a series of technical problems need to be solved such as air/fuel gas ratio and its control, ignition in-advance angle and its control, etc. In addition, attention should also be directed to the R&D of control schemes, sensors and anti-interference measures, etc. Research should be carried out for the matching of imported devices and vehicles made in China and on the basis of testing and analysis on imported devices, CNG device optimized design should be completed and improvements of CNG engines and auto vehicles and their design, tests on their design, performance and reliability should also be carried out.
    2) Technologies necessary for manufacturing natural gas powered auto vehicles should be popularized for spread use, e.g. special compressor for
natural gas, natural gas absorption technology, compressed natural gas cylinders for vehicles'use (including glass fiber twine or carbon fiber twine compressed natural gas cylinders for vehicles'use), etc. In this respect, Xi'an Jiaotong University has already started its R&D on natural gas compressors, which has produced optimal results. On the other hand, technical breakthroughs have been realized by Xi'an Xiangyang Aerospace Industry Co. in the R&D on compressed natural gas cylinders for light type vehicles'use. The products have passed technical appraisals and will be put into batch production.
      3)The supporting facilities for R&D activities linked with the two above- mentioned technical issues should be established, which include experimental platforms, laboratories and advanced manufacturing technologies, etc. The most important is the analogue experiment platform for mixed gas, CNG auto vehicle comprehensive testing system, laboratories for natural gas powered auto vehicle technology and product testing and evaluation, natural gas powered auto vehicle retrofitting specifications, technical conditions for natural gas powered auto vehicles and quality guaranteeing system, CIMS and advanced manufacturing technologies.
    4.2 Measures to be taken
    1) Supporting policies are to be worked out
    With its nature giving a helping hand to energy structure readjustment
and environmental protection, the natural gas powered auto vehicle industry is in fact a promising industry that not only brings benefits to the present generations, but also prepares a better life for the future generations as well. The production and operation of natural gas powered auto vehicles is also a huge system engineering that is closely linked with many sectors such as machine building, electronics, urban planning and construction, land planning, safety, norms and standards, taxation, testing and environmental protection, etc. A fast and sustainable development of this industry is undoubtedly built on the basis of powerful support coming from all sectors, authorities and the entire society. All foreign countries that promote the development of natural gas powered auto vehicle industry without any exception have worked out supporting policies that offer optimally preferential treatment to this rising industry. Our suggestion is, the competent governmental authorities are to play their roles of providing guidance, coordination, support and obstacle removing, and to stipulate relevant rule and regulations to protect this industry. In Xi'an, preferential policies should also be worked out for gas price subsidies (the present gas prices in Xi'an are still too high which is not helpful to its spread use) as well as for road toll, etc. Otherwise, the natural gas powered auto vehicle industry can not spring up.
    2) The new industry calls for compulsory rules
    Considering its important functions in strengthening environmental protection and controlling air pollution, we suggest that the competent government authorities consider implement administrative and legal means, in addition to the conventional economic means, to check the pollution resulting from the auto tail gas emission. It is advisable to encourage the retrofitting of conventional auto vehicles into natural gas powered vehicles by implementing stricter air quality standards and emission standards for different types of auto vehicles. As for the vehicles used by governmental organs, enterprises and public institutions, a certain amount of natural gas powered auto vehicles should be arranged on a year's basis.
    3) Opening up funding sources to collect as much funds as possible
    With very large amount of work, the new industry needs large amount of
capital to put in not only the construction of gas refilling stations and
retrofitting projects, but also the supporting activities such as auxiliary technology development, norms and standards stipulation, setting up testing centers and training centers, etc. Since funds from the government and some certain firms are not sufficient, it is necessary to collect money from as many sources as possible. Input and investment from domestic enterprises, institutions, as well as financial support from overseas environmental protection organizations, etc. are all encouraged and highly appreciated. It is also possible that once the company is established bonds can be issued to the whole society to collect money. At the same time, it is sincerely hoped that the competent state authorities could exercise an inclination policy to such a promising industry by providing appropriate amount of financial support.
    4) Focus on talent development and training
    The natural gas powered auto vehicle is the embodiment of civilization, but its industrialization will rely on intelligence. In the time of “intelligent economy", the key to the economic acceleration is the development of human intelligence. In the course of industrialization of natural gas powered auto vehicles, importance is to be attached to the development of talents of decision-making type, technological type, manipulation type and hard working type. In this way, human resources structure can be perfect which is a must to a consolidating industrialization of gas powered vehicles. On the other hand, it is of equal importance to set up training center so as to create conditions for the spread use of natural gas powered auto vehicles.
    5) Implement technical norms and standards to the full
    To ensure the safety and product quality, an enhanced management based
on strict norms and standards is necessary. Strict technical norms and standards will have to be worked out for the design of gas refilling stations, manufacturing of natural gas cylinders, components for vehicle retrofitting, and assembling and testing, etc. to realize a standardized management. In this regard, strict norms and standards have already been put into practice in countries such as the U.S., Australia, Italy, New Zealand, Japan, Argentina, Canada and Switzerland, etc. The International Standards Organization (ISO) and the European Standards Commission have also stipulated relevant norms and standards. Over the past few years, China has also worked our norms and standards regarding natural gas powered auto vehicles based on the actual conditions in China. At the same time, a standardization management system has been gradually established to ensure the implementation of all norms and standards. In the course of gas powered vehicle industrialization, it is a must to implement the norms and standards stipulated by the state to the full. In the case no state standards can resort to, local standards or enterprise standards are to be worked out by reference to international norms and standards to govern the whole management process of product design, manufacturing, assembling, testing and experiments. The imported equipment should also undergo appraisal and acceptance based on relevant standards.
    6) Create a good public opinion by intensified popularization promotion
    As is just in the starting phase, natural gas powered auto vehicles in
our country have not yet won wide understanding and acceptance in the general public. It is very natural that wide spread doubt does exist about the safety characteristics of natural gas powered vehicles and the same is true of the public opinion about the gas powered vehicles' role in reducing
environmental pollution. It is therefore very important to intensify promotion campaign to create a positive public opinion atmosphere so that natural gas powered vehicles win the widest acceptance and support from the general public. Once these are achieved, an optimal market environment will
be in place for the gas powered auto vehicles.
    7) Push forward technical advancement and industrialization by strengt
hened technical intercourse and cooperation
      Nowadays in many countries, comparative mature technologies and advanced equipment as well as strict norms/standards and management experiences have already become available for utilizing natural gas as a substitute auto vehicle fuel for petrol. An enhanced technical exchange with these countries will surely facilitate us to learn more experiences and lessons, and obtain the latest information and data concerned, which in turn will facilitate our import of advanced technologies and equipment from abroad thus further activating the technical advancement and the natural gas powered auto vehicle industry.