1.1. Topic Background and Significance
The invention of automobile is an important symbol of modern civilization. In 2014, car ownership around the world has exceed 1.24 billion. With urbanization in emerging economies, industrialization development and booming buying demand, this figure will continue to rise. As for Chinese market, by the end of 2015, car ownership has reached 172 million vehicles, a net increase of 17.81 million compared with that of 2014. While automobile has brought great convenience to human beings, it has also caused serious energy crises and environmental pollution. Figure 1 below is about world auto market growth(Ahuja,2014).
In terms of energy, the current proven oil reserves reach 1.3 trillion barrels (Qian,2010). If there will be a consumption of 85 million barrels per day, then the oil will run out about 40 years with transportation energy consumption accounting for 62%. Although China's oil reserves rank among the top ten in the world, as a country with high energy consumption, recoverable oil reserves in China can meet the energy demand for less than a decade. In 2015, Chinese oil imports exceeded 60% for the first time(Sun,2011), and the proportion is still rising rapidly. Therefore, it is necessary to reduce the oil consumption for transportation.
In terms of environment, the world is now facing severe challenges of climate change. And extreme weather has occurred frequently in recent years. The key to tackling these problems lies in concentration rise of carbon dioxide in the atmosphere, which prevents heat from escaping from the earth into space, thus causing melting glaciers and regional climate anomalies. Vehicle emissions are the main source of carbon dioxide. And car fuel will produce nitrogen dioxide, carbon monoxide, nitric oxide, volatile organic compounds and other harmful substances, which will cause air pollution and do a harm to human health ultimately. automobile exhaust from fossil fuel combustion accounts for more than 22% of the environmental pollution source(Fang, Cai & Zhang, 2015). Facing with serious energy crisis and environmental pollution, the development of efficient and energy-saving new type of cars will become the future direction of the automobile industry.
Battery electric vehicle is a new energy vehicle driven by motor and is powered by on-board power supply, including accumulator or other energy storage elements. Although it has a history of about 150 years, which is 60 years earlier than the internal combustion engine, the application scene and scale have been limited. The reason is that there is limit of battery or super capacitor energy density. Therefore, single charge range of electric vehicles much shorter than that of traditional cars. According to electric vehicles in the market, endurance mileage of most electric vehicles is within 200km with the biggest one reaching at about 300km (China is colored). What’s more, the price of electric vehicles is 2-3 times higher than traditional cars and the popularity of charging facilities and other ancillary equipment also remain as a difficulty. There is a subsidy for battery electric vehicle in China, which is only available for public services. Individual owners can not enjoy the subsidy. So, although battery electric vehicle is the future development trend (Liu. 2006), it still can’t get its mass popularization in China currently.
Fuel cell vehicle is a new type of car with research significance. It is powered by hydrogen and the emission is pure water without any pollutants, achieving zero pollution in deed. And the energy density is higher than other types of battery cars, so many countries have invested huge sums of money and talents to make research and development. However, in view of hydrogen production cost and hydrogen battery’s weak adaption to environment, there still will be 10 to 15 years before the industrialization of fuel cell vehicles (He, 2012).
Hybrid electric vehicle is a vehicle consisting of two or more single drive systems that can be operated simultaneously. The power required for movement is provided by a single drive system or multiple drive systems according to the actual travel conditions of the vehicle. Hybrid power system not only has the advantages of superior engine performance and long endurance, but also has the characteristics of no pollution and low noise. It is one of the most popular models at present.