對于很多司機來說，夏天開車最難以忍受的就是高溫。好在汽車空調的存在大大提升了駕駛舒适度。不過有些人也因為擔心油耗問題而選擇開窗降溫。在一定溫度條件下，開窗和開空調，都可以達到降低車内溫度的目的。那麼，究竟哪一種方式更加省油？
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There are two main factors to consider when approaching this question. The first deals with how the air compressor in your car works and how much extra fuel the engine has to use to keep it running. The second is what is known as air resistance or drag. Drag is the resistance that cars, and all moving objects, encounter when moving through the air at any speed. Most modern cars are designed to be relatively aerodynamic, which allows them to pass through the air with minimal resistance.探讨這個問題時需要考慮兩個主要因素。第一個與汽車中的空氣壓縮機的工作方式有關，以及引擎需要使用多少額外的燃料來保持其運作。第二個因素是所謂的空氣阻力或阻力。阻力是指汽車和所有移動物體在任何速度下移動時所遇到的空氣阻力。大多數現代汽車的設計都是相對符合空氣動力學的，這使得它們能夠以最小的阻力穿過空氣。
However, when a vehicle has its windows down, air passes into the car where it was formerly allowed to flow over it, causing resistance that didn't exist when the windows were up. You can think of it a bit like a parachute. When a skydiver opens up the parachute, it cups the air and causes a massive amount of drag, enough to slow the speed of the skydiver and allow him or her to land safely on the ground. Unlike the parachute, you definitely don't want a lot of drag on your car because it makes your engine work harder to get your vehicle up to the same speed.然而，當車輛将車窗搖下時，空氣進入車内，而以前允許空氣通過的地方現在産生了阻力。你可以想象成一把降落傘。當跳傘者展開降落傘時，會兜住空氣并産生強大阻力，足以減緩跳傘者的速度，使他們安全降落。與降落傘不同的是，我們不希望車輛遇到太多阻力，因為在車速不變的情況下這會讓引擎消耗更多燃料。
So, does drag really affect a car's fuel economy more than air conditioning? There are times when using the AC will save you gas.那麼，開窗的空氣阻力會比開空調更耗油嗎？什麼時候開空調更省油？
Back in 2004, the Society of Automotive Engineers (SAE) conducted a study at a General Motors wind tunnel and on a desert track. In the wind tunnel, air was forced over the front of the car and also from an angle on the front of the car to simulate a cross wind. In the desert, temperatures and vehicle speed were factored into the study. Two vehicles were used in the test, one was a full-size SUV with an 8.1-liter V-8 engine and the other was a full-size sedan equipped with a 4.6-liter V-8 engine. Overall, both studies showed that driving with the windows down has a significant negative effect on the fuel efficiency — more than using the vehicle's air conditioner.早在2004年，美國汽車工程師學會(SAE)在通用汽車公司的風洞和沙漠賽道上進行了一項研究。在風洞中，空氣需要穿過汽車前部，從汽車前部的一個角度來模拟側風。在沙漠中，測試研究了溫度和車速的影響。測試使用了兩輛車，一輛是8.1升V-8發動機的大型運動型多用途汽車（SUV），另一輛是配有4.6升V-8發動機的全尺寸轎車。總體而言，兩項研究都表明，将車窗搖下來對燃油效率的負面影響要大于使用車輛的空調。
For the sedan, when the windows were down, the efficiency was reduced by 20 percent, while the SUV fuel efficiency was reduced just 8 percent [source: Hill]. These differences are an important factor in determining just how much the windows down option will affect the fuel efficiency of your vehicle. The study concluded that the more aerodynamic the vehicle, the more drag open windows will create.當車窗搖下來時，轎車的燃油效率降低了20％，而SUV的燃油效率僅降低了8％。這些差異是決定車窗關閉選項對車輛燃油效率影響程度的重要因素。研究得出的結論是，車輛的空氣動力學設計越強，打開車窗産生的阻力就越大。
However, with newer, more efficient vehicles the difference is likely to be negligible. 然而，對于更新、更高效的車輛，這些差異可能可以忽略不計。
Since no tests have been conducted on an extensive array of vehicles, here are some :由于沒有對大量車輛進行測試，以下是一些概要指南：
When you're driving around town at relatively low speeds, you'll use less gas by switching the air conditioner off and rolling down the windows. It's more efficient to drive with the windows down at slow speeds as opposed to faster speeds because there's less aerodynamic drag when you're driving slower [source: Motavalli].當市區以相對較低的速度行駛時，關閉空調，将車窗搖下來可以節省燃油。在低速行駛時，打開車窗比在高速行駛下燃油效率更高，因為在低速行駛時的空氣阻力要小一些。
If you're searching for a good rule-of-thumb number for when it's best to open the windows and switch off the air conditioner, the cut-off should be around 40 mph (64 kph) for larger vehicles [source: Arthur]. With smaller vehicles, like the Corolla, you could use the AC and get up to 70 to 80 mph (assuming that's a speed limit where you are) without using extra gas.
如果你需要一個經驗法則，來确定什麼時候打開車窗并關閉空調最合适，那麼大型車輛的速度上限應該在64公裡/小時左右。對于卡羅拉等小轎車，低于113-129公裡/小時(假設你所在的地方的限速為此範圍)的速度開窗行駛不額外消耗燃料。
編輯：董靜
來源：中國日報網