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標題: [教學] Direct fuel injection vs port fuel injection [打印本頁]

作者: carwing    時間: 2009-2-9 01:28 PM     標題: Direct fuel injection vs port fuel injection

By Jim Kerr

There are a few car owners who prefer the simplicity of thevehicle fuel systems that existed before fuel injection was introduced:a mechanical fuel pump, a carburetor and a few hoses, and the fuelsystem was complete. Although these systems may have been simple, theywere far from trouble-free. Carburetors often required overhauls orcleaning. Sticking choke mechanisms either meant the vehicle wouldn’tstart or it would start but pour black smoke (unburned fuel) out thetailpipe. Many vehicles required the carbs to be adjusted every springand fall as temperatures changed. The fact is, fuel injectioneliminated most of these problems.
Early fuel injection systems could be grouped into two types: portand throttle body. Throttle body injection places the fuel injectors ina central housing similar to a carburetor that sprays fuel into theintake manifold. These systems were economical to produce but had someof the disadvantages of carbs. Fuel had to travel through the intakemanifold with the incoming air, so manifold design had to be simple.Place a few curves in the manifold and fuel would drop out of theairflow. Then the air fuel ratio wouldn’t be the same for allcylinders.
Port injection however, sprays the fuel into the intake ports of thecylinder heads at the back side of the intake valves. This allowed theengineers to design manifolds that directed only air, so they could beany length and shape. Better volumetric efficiency was achieved (bettercylinder filling) with these new manifold designs, so fuel economyimproved along with better power.
Regardless of the type of fuel delivery system, the goal is to havea 14.7 to 1 air to fuel ratio in the combustion chamber as it burns.The reasoning for this is simple: current catalytic converters are two-stage devices. One stage works best with rich air fuel ratios (below14.7 to 1) and the other stage works best with lean air fuel ratios(above 14.7 to 1). Only at 14.7 to 1, the stoichiometric ratio, doesthe catalytic converter reduce emissions properly: that is why vehiclesoperate at this air fuel ratio.
If we had converters that worked effectively at leaner air fuelratios, then engines could be programmed to operate at a leaner ratioand we would have better fuel economy, but research hasn’t produced acost-effective one yet. You can be assured they are working on it,though.
Direct fuel injection is the newest type of injection system on theNorth American market. Companies such as Nissan and Mitsubishi have hadsystems overseas for several years, but it was only in the past fewyears that materials and manufacturing technology improved so thatdirect fuel injection would meet our emission standards.
Today, many companies produce vehicles with direct fuel injectionand others will soon. You don’t have to look under the hood of a luxurycar either. Mazda and Chevrolet have direct fuel injection on lowerpriced vehicles already.
So why choose direct fuel injection? Better fuel economy and morepower are the benefits. Direct fuel injection can increase fuel economyby 15 to 20 per cent and when combined with turbocharging, may see 20to 30 per cent economy improvements. A 15 per cent increase in poweroutput is possible at the same time.
Direct fuel injection sprays the fuel directly into the cylinderinstead of the intake port like a port injection system. The differencein position is small, but it decreases the surface area that fuel cancome in contact with before it ignites. If fuel comes in contact withthe sides of the cylinder, the back of the intake valve or the intakeports, some of it condenses into fine droplets. Fuel only burns afterit becomes a vapour, so these droplets pass through the combustionchamber without being burned. Direct fuel injection reduces thispossibility.
Direct fuel injection sprays the fuel into the combustion chamber ata much higher pressure. Some systems operate in the 2,000 to 3,000 psirange and if you listen closely under the hood, you can hear themechanical clicking of the injector solenoids and pressure regulator asthey control fuel spray. This is normal. The higher pressure causes thefuel to come out of the injector in a very fine mist that will quicklyturn into vapour.
High swirl combustion chamber designs and/or turbocharging are oftenused in conjunction with direct fuel injection to mix the fuel with theair faster. More power, better fuel economy and better engine controlmake direct fuel injection the way of the future for gasoline engines.

[ 本帖最後由 carwing 於 2009-2-10 10:42 PM 編輯 ]
作者: carwing    時間: 2009-2-10 01:18 PM

有一些車主誰更喜歡簡單的車輛的燃料系統之前存在噴油介紹:機械燃油泵,一個化油器和少數軟管,和燃料系統已經完成。雖然這些系統可能已被簡單,他們是遠離無故障。.化油器往往需要大修或清潔。 堅持扼流圈機制要么意味著車輛將無法啟動或將開始,但爭取黑煙(未燃盡的燃料)的排氣管。.許多車輛的碳水化合物需要加以調整每年春季和秋季的溫度變化\。事實上,燃油噴射消除大部分這些問題。

.早期燃油噴射系統,可分為兩種類型:港口和節氣門體。節氣門體注入的燃料噴射器的地方在中央住房類似的噴射燃料化油器的進氣歧管。這些系統的經濟生產,但一些缺點碳水化合物。燃油穿越進氣歧管與新任空氣,所以多方面的設計要簡單。地方少數曲線形和燃料將退出氣流。然後空燃比不會是相同的所有氣瓶。

港注射然而,噴霧劑的燃料進入進氣道的氣缸蓋在背面的攝入量閥。這使工程師設計流導向只有空氣,所以他們可以是任何長度和形狀。容積效率更好地實現(更好地缸灌裝)有了這些新的流形設計,使燃油經濟性提高以及更好的電源。

.不論什麼類型的燃料供應系統,目標是到了14.7比1的空氣燃料比在燃燒室因為燒傷。其理由很簡單:目前的催化轉換器是兩個階段的設備。最好的一期工程具有豐富的空氣燃料比(以下14.7 1 )和其他階段的最有效精益空氣燃料比(以上7月14日至1 ) 。僅在7月14日為1 ,化學計量比,沒有催化轉換器減少排放量的正確:這就是為什麼運營車輛在此空燃比。

如果我們有轉換工作的精幹有效的空氣燃料比,然後進行編程引擎可以運行在一個精簡的比例,我們將有更好的燃油經濟性,但研究沒有產生具有成本效益的一個還沒有。你可以放心,他們正在研究它,但。

直接燃油噴射是最新型的噴射系統的北美市場。 ,如日產和三菱商事有系統幾年來在海外,但它只是在過去幾年中的材料和製造技術的改進,以便直接燃油噴射將符合我們的廢氣排放標準。

今天,許多企業生產的車輛直接燃油噴射和其他將很快。您不必期待引擎蓋下的豪華車的。馬自達和雪佛蘭直接燃油噴射的低價格的車輛已經。

那麼,為什麼選擇直接燃油噴射?更好的燃油經濟性和更大的權力的好處直接燃油噴射的燃油經濟性可以提高15至20時,百分之結合渦輪增壓,可以看到二十至百分之三十的經濟改善。增加百分之十五的輸出功率有可能在同一時間。

直接燃油噴射燃料直接噴入汽缸,而不是像進氣道噴射系統端口。立場上的差異很小,但它減少了表面積,燃料可以接觸面前點燃。如果燃料接觸與雙方的缸,背面的進氣閥或進氣道,有些凝結成水滴罰款。燃料燃燒後只變成蒸氣,所以這些液滴通過燃燒室而不被燒毀。 直接燃油噴射降低了這種可能性。

直接燃油噴射的燃油噴射到燃燒室在高得多的壓力。有些系統在2000年至3000防擴散範圍,如果你仔細聆聽引擎蓋下,你可以聽到機械點擊的噴油器電磁閥和壓力調節器,因為它們控制燃油噴射。這是正常的。 較高的壓力,導致燃料走出注射器在一個非常霧濛濛,將很快變成蒸汽。

高渦流燃燒室的設計和/或增壓經常被用來與直接燃油噴射混合燃料與空氣更快。更多的權力,更好的燃油經濟性和更好的發動機控制直接燃油噴射的方式為未來的汽油發動機。




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