听力文摘：气泵上的辛烷值是什么意思?

At the gas pump, you have a choice of octane numbers.87? 93?

气泵上有两个辛烷值，87和93。你会选择哪个？

What's the difference?

这两个数字有什么不同呢？

To explain octane numbers,let's take an imaginative leap into the internal combustion¹ engine of a car.

为了解释辛烷值，让我们富于想象力的思维先跳跃到汽车的内燃机上面。

Inside the cylinders³ are combustion chambers⁴ where a mixture of gasoline and air burns.

气缸内部是供汽油和空气的混合物燃烧的内燃室。

Normally, the spark plug ignites the mixture and the pressure from the resulting explosion pushes the piston⁶ down.

正常情况下，火花塞会点燃这种混合物，爆炸产生的压力会推下活塞。

But, if the fuel is not matched to the engine, the heat in the cylinder² can ignitethe fuel even before the spark plug fires.

但如果燃料和发动机不匹配，气缸的热量在火花塞点火前就会点着燃料。

This early ignition causes pressure waves that rattle⁷ the piston, making a knocking sound.

提前点着燃料会引发压力流，使活塞咔哒咔哒作响，发出爆震音。

It can also overheat the spark plugs, erode⁸ the combustion chamber⁵, and make the car run inefficiently⁹ and roughly.

同时，会使火花塞过热、燃烧室产生磨损，使得汽车在行驶过程中效率低下并且无法平稳运行。

Octane numbers, also known as antiknock ratings, tell you how resistant¹⁰ gasoline is to knocking.

辛烷值也称为抗爆性指标，表示汽油的抗爆性。

Gas at the pump has been tested in a lab, where it's compared to two reference fuels.

泵里的汽油是经过实验室检测的，另两种参考燃料会在实验室内与其进行对比。

The first isvery knock resistant, rating 100 on the knock resistance scale.

第一种抗爆性极好，辛烷值达到100。

The second knocks easily and rates a lowly zero.

第二种易产生爆震，辛烷值很低，为零。

The two are combined to make comparison mixtures.

我们把两种燃料混合起来做成用于对比的混合油，

Gas with an octane number of 87, when tested, acted just like the comparison mixturewith 87% knock resistant fuel.

发现在试验过程中，辛烷值为87的汽油和含有87%抗爆剂的混合油效果一样。

So,the higher the octane number, the more resistant to knocking.

因此，辛烷值越高，抗爆性就越强。

If your engine doesn't knock with lower octane gas, there's no reason to spend more on higheroctane.

如果发动机在使用较低辛烷值汽油的情况下不发生爆震，那就没有必要在较高辛烷值的汽油上花更多的钱。

Because knocking depends partly on the engine's compression ratio, some engines need higher octanes to prevent it.

因为爆震现象部分取决于发动机的压缩比，一些发动机会需要较高辛烷来防止爆震。

Owner's manuals often specify¹¹ the right octane for your engine, andyour ears are a good measure, too!

车主的实用手册上通常会写明适合发动机的辛烷，而你的耳朵同样也是检测爆震的好工具。

1 combustion   

n.燃烧；氧化；骚动

参考例句：

• We might be tempted to think of combustion.我们也许会联想到氧化。
• The smoke formed by their combustion is negligible.由它燃烧所生成的烟是可忽略的。

2 cylinder   

n.圆筒，柱(面)，汽缸

参考例句：

• What's the volume of this cylinder?这个圆筒的体积有多少？
• The cylinder is getting too much gas and not enough air.汽缸里汽油太多而空气不足。

3 cylinders   

n.圆筒( cylinder的名词复数 )；圆柱；汽缸；（尤指用作容器的）圆筒状物

参考例句：

• They are working on all cylinders to get the job finished. 他们正在竭尽全力争取把这工作干完。 来自《简明英汉词典》
• That jeep has four cylinders. 那辆吉普车有4个汽缸。 来自《简明英汉词典》

4 chambers   

n.房间( chamber的名词复数 )；（议会的）议院；卧室；会议厅

参考例句：

• The body will be removed into one of the cold storage chambers. 尸体将被移到一个冷冻间里。 来自《简明英汉词典》
• Mr Chambers's readable book concentrates on the middle passage: the time Ransome spent in Russia. Chambers先生的这本值得一看的书重点在中间：Ransome在俄国的那几年。 来自互联网

5 chamber   

n.房间，寝室；会议厅；议院；会所

参考例句：

• For many,the dentist's surgery remains a torture chamber.对许多人来说，牙医的治疗室一直是间受刑室。
• The chamber was ablaze with light.会议厅里灯火辉煌。

6 piston   

n.活塞

参考例句：

• They use a piston engine instead.他们改用活塞发动机。
• The piston moves by steam pressure.活塞在蒸汽压力下运动。

7 rattle   

v.飞奔，碰响；激怒；n.碰撞声；拨浪鼓

参考例句：

• The baby only shook the rattle and laughed and crowed.孩子只是摇着拨浪鼓，笑着叫着。
• She could hear the rattle of the teacups.她听见茶具叮当响。

8 erode   

v.侵蚀，腐蚀，使...减少、减弱或消失

参考例句：

• Once exposed,soil is quickly eroded by wind and rain.一旦暴露在外，土壤很快就会被风雨侵蚀。
• Competition in the financial marketplace has eroded profits.金融市场的竞争降低了利润。

9 inefficiently   

adv.无效率地

参考例句：

• The small family farm is steeped in inefficiently and struggles just to survive. 小农场主陷于无效率的境况中，只为生存下去而苦苦挣扎。 来自辞典例句
• You can't afford to run businesses inefficiently in this day and age. 在现今，经营商店无能是不行的。 来自互联网

10 resistant   

adj.(to)抵抗的，有抵抗力的

参考例句：

• Many pests are resistant to the insecticide.许多害虫对这种杀虫剂有抵抗力。
• They imposed their government by force on the resistant population.他们以武力把自己的统治强加在持反抗态度的人民头上。

11 specify   

vt.指定，详细说明

参考例句：

• We should specify a time and a place for the meeting.我们应指定会议的时间和地点。
• Please specify what you will do.请你详述一下你将做什么。