Inside the car is a motor called a gasoline engine. It is sometimes called an internal combustion engine（內(nèi)燃機(jī)）.

The engine runs on gasoline because that liquid can be easily changed into a gas， or vapor（蒸氣）. A mixture of air and gasoline vapor is easily set on fire， as with a spark². And this mixture burns so fast that it makes an explosion³ of hot， expanding gas.

In a typical car， the engine has six or eight little chambers （腔，室） or cylinders （汽缸）. These take turns （輪流） having their explosions and pushing on pistons （活塞）that then take turns pushing on a long crank（曲柄，曲軸） to make it go round and round.

Between the explosions， each cylinder must get rid of the old， hot gas inside and then be filled with fresh air and gasoline vapor for its next explosion. Having several cylinders taking turns helps the engine run smoothly.

注釋：

1．gasoline n．汽油

2．spark n. 電火花，（火花塞里的）控制放電裝置

3．explosion n．爆炸

在汽車(chē)內(nèi)部有一個(gè)被稱作汽油發(fā)動(dòng)機(jī)的馬達(dá)，有時(shí)又被稱為內(nèi)燃機(jī)。

發(fā)動(dòng)機(jī)依靠汽油運(yùn)轉(zhuǎn)，因?yàn)檫@種液體可以很容易地變?yōu)闅怏w，或者說(shuō)蒸氣?？諝夂推驼魵獾幕旌蠚怏w很容易被點(diǎn)燃，比如電火花。這種混合氣體燃燒得非?？?，可以使熱氣體膨脹后爆炸。

在一輛典型的小汽車(chē)?yán)?，發(fā)動(dòng)機(jī)有6個(gè)或8個(gè)小小的腔室，或者叫汽缸。這些汽缸中輪流發(fā)生爆炸并推動(dòng)活塞，活塞又輪流推動(dòng)長(zhǎng)長(zhǎng)的曲軸不停地運(yùn)轉(zhuǎn)。

在每次爆炸的間隙，每個(gè)汽缸必須排放掉里面燃燒過(guò)的熱氣，然后補(bǔ)充新鮮的空氣和汽油蒸氣以備下次爆炸。幾個(gè)汽缸輪換產(chǎn)生爆炸就可以使發(fā)動(dòng)機(jī)平穩(wěn)地運(yùn)轉(zhuǎn)起來(lái)。