1、Unit Nine Electric Vehicles andNatural Gas Vehicles Passage BNatural Gas Vehicles Nowadays,cars that run on natural gas as a cleaner fuel source are growing in popularity Natural gas vehicles have lower emissions compared with conventional cars running on diesel or gasoline The fuel economy,accelera
2、tion and cruising speed of an NGV is typically no less than that of a conventional car The cost of natural gas is significantly less than that of diesel and gasoline Whats more,it is safer Natural gas vehicle(NGV)can run on compressed natural gas(CNG)or liquefied natural gas(LNG)(see Fig.9-5).CNG re
3、fers to that natural gas is compressed about to 20 MPa and stored in a gas cylinder like a fuel tank on a car CNG is colorless,odorless,transparent and lighter than air with high quality heat Its main composition is methane CNG is commonly used on most of cars and light vehicles LNG refers to that n
4、atural gas is liquefied by cooling to 162 degrees Celsius below zero under the normal pressure So it is a kind of clear,colorless,non-toxic,non-corrosive liquid Its volumetric energy density is as 3 times as CNG So vehicle running on LNG has a driving range longer than that on CNG after each refueli
5、ng Many large trucks and some buses use LNG as power source Different states of natural gas must use different gas cylinders in structures to store Gas cylinders for CNG have several types made of different materials In order for natural gas to remain in a gaseous state in the gas cylinder,the press
6、ure must remain about 20MPa At present,compressed natural gas vehicles(CNGV)mostly use all-metal gas cylinder and hoop-wrapped gas cylinder which is wound with glass fiber around the surface of the gas cylinder(see Fig.9-6).The all-metal gas cylinder is low in cost,but heavy in weight The hoop-wrapp
7、ed gas cylinder is lighter in weight and more expensive than all-metal gas cylinder Usually the gas cylinder is mounted in the trunk of the car(see Fig.9-7).CNG supply system is consisted of three sections:gas storage and supply section including gas cylinder,gas fill valve and pressure line;pressur
8、e reducing section including pressure regulator and gas filter;and control section including CNG solenoid valve and gas injectors At a filling station CNG is filled into the gas cylinder through the gas fill valve(see Fig.9-8).In operating,the gas goes out of the cylinder and travels along the high
9、pressure line to the pressure regulator which reduces the pressure After the pressure reducing,the gas moves to the gas filter through the low pressure line to remove the dirt and reaches to the fuel injectors which inject the gas to the combustion chamber for burning just as gasoline does The CNG s
10、olenoid valve is only used as a gasoline-gas-shifting switch on a bi-fuel vehicle Liquefied natural gas vehicles(LNGV)have cryogenic liquid cylinders The cylinder of this kind comprises stainless steel inner shell and outer shell The inner shell stores LNG and the outer shell protects the inner shel
11、l Between them there is a winding heat insulated interlayer so as to keep the LNG cool When the engine is started,the fluid of LNG flows from the cylinder to the carburetor to convert liquid state of natural gas into gas From that point on,the fuel supply process is similar to the system on CNG-fuel
12、ed enginesNew Words and Expressions significantly signifikntli adv 值得注目地 methane mi ein n 甲烷,沼气 toxic tksik adj 有毒的 corrosive krusiv adj 腐蚀的 volumetric vljumetrik adj 体积的,容积的 density densti n 密度 hoop hup n 箍、铁环 fiber faib n 纤维 cryogenic kraidenik adj 冷冻的,低温的 filling station加油站New Words and Expressions carburetor kbret n 汽化器 gas cylinder气瓶 gaseous state气态 liquid state液态 gas fill valve加气阀 pressure line高压管路 pressure regulator压力调节阀 gas filter气体滤清器 gas injector燃气喷嘴 bi-fuel双燃烧
