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🎁 中英文稿：
If you've gone shopping for a car lately, you might have noticed that fuel economy—the number of miles per gallon—is creeping up. One reason is a more efficient type of fuel injection, called gas direct injection. It’s a feature of half the new cars sold in the U.S. last year.
如果你最近買了一輛車，你可能已經注意到——燃油經濟，每加侖行駛的總英里數正在蠕升。原因之一在於燃油噴射的效率更高，稱為缸內噴氣。這是去年所出售的一半新車所具有的一大特徵。
"With that kind of engine design you can also introduce turbocharging—that's really what it comes down to: more engine power with a smaller engine." Naomi Zimmerman, an air-quality scientist at Carnegie Mellon University—who has never owned a car. "Probably because I did a whole PhD on engine emissions."
Here's how the two injection methods differ. In the old standard, called "port fuel injection," gas is injected into the air intake, where it mixes with air before hitting the cylinder. In direct injection though, as the name implies, the fuel is injected directly into the cylinder. It's more fuel efficient, meaning lower CO2 emissions, which will help slow climate change. But paradoxically, it also emits more particulate matter, including black carbon, or soot—a pollutant implicated in global warming.
這種類型的引擎設計，也可以引進渦輪增壓——這才是真正的原因——更小馬力的引擎，更多的發動機功率。拿俄米齊默爾曼，卡內基梅隆大學一名空氣品質科學家——從未擁有一輛車。“可能是因為我博士研究生階段做了關於發動機排放的整體研究。這是這兩種噴射形式的不同之處。按照舊標準，稱之為“氣門式燃料噴射”，將氣體注入進氣口，在衝擊汽缸之前與空氣混合。然而，直接式燃料噴射，顧名思義，燃料直接注入汽缸，這樣更省油，意味著較低的二氧化碳排放，這將有助於減緩氣候變化。但是，與此相矛盾的是，也能噴射出更多的顆粒物。包括黑碳或煤灰——與全球變暖有直接關係的污染物。
Zimmerman and her colleagues analyzed studies of direct injection engines to see how this pollution tradeoff works out for the climate. "The answer is that it's really complicated and it's not certain." But on average, she says, boosting fuel economy five to nine percent would probably cancel out the warming effects of black soot, and score a net positive for the climate. The findings are in the journal Environmental Science and Technology. [Naomi Zimmerman et al., Assessing the Climate Trade-Offs of Gasoline Direct Injection Engines]
齊默爾曼與她的研究團隊對直噴式發動機的研究進行分析以查明這一污染權衡怎樣使氣候受益。“答案是，這真的很複雜，目前還不能確定。”但平均而言，她表示，將燃油經濟性由5%提高到9%，可能會消除黑炭的暖化效應，整體而言對氣候有益。該項研究結果發表在《環境科學與技術》雜誌上。
The fuel economy goal might be different in places with big temperature swings, and where gasoline has more aromatic compounds—which seem to boost black carbon emissions. One place that fits the bill: Canada. “There we might need to be closer to the 10 percent, 15 percent mark in terms of improving fuel economy. Which is actually a very aggressive increase in fuel economy."
