1、Unit Nine Electric Vehicles andNatural Gas Vehicles Passage BNatural Gas VehiclesNowadays, 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, acceler

2、ation 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 saferNatural gas vehicle (NGV) can run on compressed natural gas (CNG) or liquefied natural gas (LNG) (see Fig.9-5)

3、.CNG refers 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 vehiclesLNG refers t

4、o that natural 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 e

5、ach refueling Many large trucks and some buses use LNG as power sourceDifferent 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

6、, the pressure 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 weigh

7、t The hoop-wrapped 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 pr

8、essure line; pressure reducing section including pressure regulator and gas filter; and control section including CNG solenoid valve and gas injectorsAt 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 t

9、ravels along the high 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

10、gasoline does The CNG solenoid valve is only used as a gasoline-gas-shifting switch on a bi-fuel vehicleLiquefied 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

11、 protects the inner shell Between them there is a winding heat insulated interlayer so as to keep the LNG coolWhen 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-fueled enginesNew Words and Expressionssignificantly signifikntli adv 值得注目地methane mi ein n 甲烷, 沼氣toxic tksik adj 有毒的corrosive krusiv adj 腐蝕的volumetric vljumetrik adj 體積的, 容積的density densti n 密度hoop hup n 箍、 鐵環(huán)fiber faib n 纖維cryogenic kraidenik adj 冷凍的, 低溫的filling station加油