我已經查看了該SE網站上有關此主題的各種問題,但我並未真正找到滿意的答案。 此處一些有關電動機與汽油發動機的扭矩和功率的評論很有幫助。其他信息也可以在此處找到。
我要問的基本問題是,假設電池技術將從現在的市售技術中大大進步。只需假設為電動機提供足夠的動力就不成問題,並且電池的重量等於燃料。
是否有可能製造出一種電動飛機發動機,以使目前的商用飛機具有與當今噴氣發動機相同的功能?
我已經查看了該SE網站上有關此主題的各種問題,但我並未真正找到滿意的答案。 此處一些有關電動機與汽油發動機的扭矩和功率的評論很有幫助。其他信息也可以在此處找到。
我要問的基本問題是,假設電池技術將從現在的市售技術中大大進步。只需假設為電動機提供足夠的動力就不成問題,並且電池的重量等於燃料。
是否有可能製造出一種電動飛機發動機,以使目前的商用飛機具有與當今噴氣發動機相同的功能?
還沒有。
要查看中程飛機,讓發動機基於 CFM56或 IAE V2500。這些發動機產生100至150 kN的靜態推力。在巡航中,由於巡航高度密度低並且以0.8馬赫的速度運動,它們的推力大大降低。讓我們使用25 kN的值-足夠使它們中的兩個可以輕鬆地將 A320機身從高空推入稀薄的空氣中。
推力的大小是力乘以速度。在 35.000 ft中以0.8馬赫的速度飛行時的速度為240 m / s,因此一台發動機產生的功率為6.0 MW。現在,讓我們看看要連續生產6兆瓦的電動機有多大和重。從鏈接的Wikipedia頁面上可以看到,結果無處不在。大型工業電機的功率不到1 kW / kg,因此我們的電機重量將超過6噸。用於電動飛機的較小型電動機的推力為10 kW / kg,即 GE90渦輪風扇的功率重量比,但按比例放大時會損失其中的一部分。請記住,即使效率達到98%,電動機也會產生120 kW的熱量-需要將其清除,在稀薄的空氣中運行也不容易。
使用當前技術,電動機可以達到2到3 kW / kg-這意味著驅動我們假設的發動機的電動機的重量為2至3噸。此外,風扇和噴氣發動機的整流罩(我們將不需要高壓部件和所有渦輪機),但是風扇重量增加了一倍,因為我們需要補償缺少的高能核心流量。這可能佔CFM56 / V2500的50%,所以我們需要再增加1.2噸。
電動機的重量是其更換零件的兩倍。在獲得當前噴氣發動機的優勢之前,還有一些工作要做,但是它具有一定的潛力,因為它不會將提供給它的能量的一半傾倒在船外熱,快速移動的嘈雜氣流中。 p>
編輯:
由於這麼多人對我感到興奮,而忽略了電推進的能量密度方面,儘管這個問題確實明確希望將其排除在外,但以下是 >兩點要考慮。能量密度只是蓄電問題的一半。
引擎很棒。電動發動機可以快速,強大且有效。我看到兩個問題:
首先-商用飛機消耗的大量能源。單引擎輸出200kN,您需要在飛機上安裝小型動力裝置。即使電池是100%有效的並且可以存儲足夠的能量,您也需要燃燒大量的燃料才能對其進行充電(您將需要大量替代能源來匹配所提供的能量)。 >第二-都是關於能量密度的。噴氣燃料的功率為34 MJ / l,電池的功率最高為120 Wh / kg = 0.36MJ / kg(根據此站點)。因此,您需要多於100倍的空間來存儲相同量的能量。
只需搜索“電動飛機”,您將獲得列表,這些列表主要是小型,超輕或自行式滑翔機,而滑翔機卻沒有不需要攜帶很多能量。
與用於航空推進的燃料燃燒相比,電池始終具有一個重要的缺點:重量保持恆定。客機(尤其是用於長途飛行的客機)在飛行過程中會燃燒掉很大一部分起飛質量。但是,電池會不斷保持其初始質量。這是一個有很多原因的問題:
最明顯的原因是,該飛行需要更多的能量。即使您獲得的電池具有與噴氣燃料相同的能量密度,並且也很穩定(我們目前還很遙遠),飛機在整個飛行過程中仍需要攜帶全部電池。因此,隨著飛行的進行,即使電池具有與燃料相同的能量密度,電池供電的飛行每英里所消耗的能量也要比燃料驅動的飛行多得多。這也意味著在相同的範圍內,甚至需要更多的電池質量,因為電池需要額外的能量。
另一個大問題是最大著陸重量。許多客機的設計並不能僅僅因為不需要而以最大起飛重量著陸。這就是為什麼有時需要將燃油傾倒或燃燒掉的原因之一,飛機起飛後遇到問題才可以再次著陸。但是,有了電池,著陸時您仍然會承受起飛重量,這意味著您將需要更堅固的起落架和輪胎,這意味著還要更多的重量和設計/製造成本。這也意味著您將更快著陸(由於額外的重量),因此您將需要更多的跑道長度才能著陸,並且需要能夠吸收更多能量的製動器。飛機的動能等於其質量乘以速度平方的一半,因此,著陸重量和速度增加時,著陸期間制動器必須吸收的能量急劇增加。
一個不太重要但仍然很重要的問題是對跑道表面的更多懲罰。由於飛機現在降落在其MTOW附近,因此跑道表面將比現在更快地受損,並且需要更頻繁地重鋪表面和/或設計用於更大的載荷。這也可能意味著,在這些跑道得到加強之前,該飛機將無法使用原本相當於燃料的飛機所能使用的那麼多跑道。
當然,您可以在電池耗盡時開始拋棄電池,但這(顯然)也有很多問題:
為了耗盡一些電池您將無法比其他任何人更快地汲取所有電池的電量,這意味著每個電池的耗電量更高(因此,每個活動電池每單位時間產生的熱量更多,等等)。
您需要設計飛機以便能夠安全地拋棄細胞。這樣做是可行的,但將需要大量的額外設計成本和額外的重量。
當您開始到處扔掉巨大的電池時,環保主義者不會太高興。業主也不會。現有的電池化學物質已經具有很強的腐蝕性,而具有Jet-A能量密度的電池化學物質可能會變得更具腐蝕性,不穩定,並且無論其掉落在哪裡,都不利。
The biggest advantage of 'going' electric is that electric fans are way more efficient than a jet turbofan. A jet turbofan creates 75-85% of its thrust from the fan and 25-15% from the 'core' exhaust stream. The principle is that slower the accelerated air is, the more efficiently you generate thrust, as moving a small volume of air very fast means you lose energy in the kinetic energy of the accelerated air mass. So, bigger (or more) fans, accelerating a larger volume of air at a slower speed is much more efficient. Jet engines already do this by connecting a large fan at the front to the compressor shaft behind it, and this is a high bypass jet engine.
Even so, modern turbofans achieve under 2 Newtons of thrust per kW of energy. This is because the engine itself has low thermodynamic efficiency coupled with the fan being sub-optimised by various constraints that do not apply to an electric fan design. For example, the fans diameter is limited by ground clearance and by the RPM of the compressor drive shaft. It still rotates much too quickly and the tip velocity is capable of going supersonic. This makes for drastic drag loses and noise issues. Consequently the bypass ratio is far too low for really high efficiency, which can only really be resolved by having multiple fans. having additional contra-rotating open blades electric fans for example around the rear of the fusilage can ingest slow air from the body of the aircraft which is more efficient, and they can be placed at multiple points along the wing and tail sections.
Electric fans can, due to the approx 4 times less thermodynamic energy loses and slower tip speed, optimal RPM and slower air exit velocity potentially exceed 20N per kW, and probably get to 35N per kW.At high speeds though I don't know what performance they would achieve but it is safe to say it is going to be a LOT better than a turbofan. Consequently a battery can potentially be competitive at around 500Wh/kg, including power electronics and wiring.
Motor weights depend on power required, since as pointed out its harder to cool a large core. However you wouldn't want to try to replace the fan on a current jet engine but have multiple lower power fans, which means that the power density in kW/kg is going to be higher than in the cases listed above, superconductors not withstanding. Smaller fans also can rotate faster, suiting these kind of motors.
As pointed out above, the REAL issue is not the battery energy density but the battery POWER density - to have not only sufficient power at take-off but also to recharge within a turn around of 20-50 minutes. Since electric aircraft would first be competitive only against short to medium haul flights, a lot of which are internal and have fast turn around times, a power density of around 1kW per kg is needed, and that exceeds the current capability of high energy density batteries by a large margin.
Theoretically, if we can gain greater thrust efficiency (say 60 Newtons per kW) then we could use a lot less energy, therefore we would only need to cycle a portion of the battery capacity and could get away with, say 500W per kg charge/discharge power). In practice the power density stated is a maximum value but occurs at lower energy efficiency and tends to shorten battery life, so the battery would need to probably have a stated power density 50% more to operate efficiently this way.
110 Newtons of thrust per kW of power has been demonstrated with electrostatic ion thrusters (the type used in 'lifters' which you can see on youtube) but this have low thrust density so you have to factor in weight. Increasing the voltage will help with that.
The issue of the plane not becoming lighter as you fly is to some extent important, but the cost saving in fuel and the potential to have many fans utilised for example to assist in airflow around the wing can increase lift at low speed and thereby compensate for increased mass through out the flight envelope. The likely embodiment of contra-rotating propellers each with electrically operated variable pitch blades that can optimise both tip velocity and angle to the conditions along with accelerating a much larger volume of air more slowly will greatly increase the overall efficiency. Electric propulsion in contra-rotating fans is much easier mechanically than one hooked to a diesel or jet turbine, and can suit the high velocity of commercial aircraft (see https://en.wikipedia.org/wiki/Propfan) which shows that contra-rotating ductless fans can offer efficiency advantages. Noise issues are a function of having to link these propellers to individual jet engines which again means high tip velocity as a product of the limitations on diameter and high RPM of the engine. When electrically powered, more fans can be used at much slower tip velocity, this slashes the noise produced.
The weight of the extra fans is partially offset by the gains from taking away the cowling both in weight and drag.
Because of the recharge issue, the likely embodiment will be advanced, higher efficiency engines that recharge the batteries once in cruise and descent, and top-up the energy required during climb. These could use superconducting generators and with an adequate battery reserve risk of catastrophic generator failures should be mitigated.
所有評論都非常真實有效。我只想補充一點,西門子已經為一台260kW飛機發動機製造並進行了飛行測試,其功率/重量比為5kW / kg,專門針對單引擎ICE型飛機,並認為該設計具有可擴展性,因此可以製造100個座位的區域系列混合動力飛機。即將成為現實。這裡需要注意的重要一點是,混合動力汽車解決了電池能量密度問題以及起飛與著陸重量之間的關係,並且電動機大大提高了傳統ICE(內燃機)的安全性。
(儘管這個問題早已得到解答,但我感到有很多可以補充的地方,因為它不斷被問到,而且技術並非完全是靜態的。)
讓我們首先看看功率/重量比率。特斯拉汽車電機的最高數量是8.5 kW / kg。電動飛機專用的Emrax 268的輸出功率約為11.6 kW / kg。
相比之下,Trent XWB在7,550 kg的包裝中以300m / s的流量提供430 kN的推力,相當於64.5 MW的功率-功率/重量比為8.5 kW / kg。但是,這不是蘋果對橘子的比例:這個比例適用於整個包裝,發動機和風扇,並測量有用的輸出,例如汽車的車輪功率。
簡而言之,渦輪發動機仍比電動機輕,但差異並不明顯。全電動發電廠無法堆疊的地方是范圍。我已經回答了另一個問題-是否有混合動力飛機?。簡短的說法是,電動飛機的最大可能射程為專用於電池的重量的每一%為10 nmi。如果堅持使用已知飛機的燃油成分,這會將電動飛機的射程限制為300-450 nmi。
但是在航空應用中,這已經足夠了。現代航空消耗的最重要的不可再生資源-1960年代塞斯納斯和派珀斯的石油供應,沒有這些資源,沒人能負擔成為飛行員-不會永遠持續下去。如果當局允許,量產的特斯拉發電廠可以為教練機和通用航空飛機提供動力,而價格僅是經認證的汽油發動機的擁有成本的一小部分。
是的。問題基本上可以歸結為:
忽略功率輸入,電動發動機能否在該噴氣發動機的尺寸和重量範圍內為該噴氣發動機提供等效的輸出?
所以:
噴氣發動機的功率重量比是否比電動發動機大?
和
https://en.wikipedia.org/wiki/Power-to- weight_ratio#Electric_motors.2FEmotive_generators
用於波音777的GE90-115B Brayton渦扇噴氣發動機的功率重量比為10.0 kW / kg。
電動用於航空的電動機EMRAX268的功率明顯較低,但達到10.0 5kW / kg。
有些人會擔心電動機是否可以按比例放大,但是在電動汽車行業中可以看到汽車隨時可用,而電動機的大小和體積相對於那些可以在加速度和最高速度方面競爭的車輛,其所需的組件(冷卻,控制)要比汽油發動機小,輕。
更能說明問題的是,電動機及其組件是不僅重量更輕,體積更小,而且價格也更便宜。
電動航空的唯一限制因素是動力源,作為向前邁出的一步,每個主要的製造商都已經在設計混合動力飛機。儘管它們具有噴氣發動機的強大功能,但其燃油效率(以及排放效率)仍未達到應有的水平。為電動發動機提供動力的噴氣燃料發電機可能在十年之內上市。
如果電動發動機無法保持其自身的尺寸,重量和功率,這些混合動力飛機將是不可能的。相對於噴氣發動機。
Roughly, potentially, but there are some key differences in the comparison of a jet engine and the theoretical 'electric jet engine', that are very different from the comparison of a car engine to a motor-driven EV.
Most notably, as previously mentioned, is the turbo-fan is mechanically driven by the combustion heat-driven expansion of the air compressed by it's compressor. At cruising speeds (where the jet engine is optimized), this is a much more fuel efficient arrangement than the cruising speed operation of an automobile combustion engine.
Basically, there are two places where the released heat is converted to mechanical energy-- first, much of the heat-release of combustion is captured by the turbine that drives the compressor. Second, the exhaust nozzle also converts heat not captured by the turbine into kinetic energy by accelerating the mass-flow through the engine, converting a pressure delta generated by heat expansion into a velocity delta through nozzle geometry. By comparison, the combustion engine converts the exhaust gas heat expansion into mechanical energy by driving a linear piston, and gains no mechanical energy by exhaust. Generally, turbines are more efficient than pistons at mechanical energy conversion. There's also a tertiary efficiency-- namely that combustion at high pressures more efficiently converts heat to pressure as the gaseous density is higher, so more of the chemical energy of the fuel is converted to kinetic energy in a jet engine than a combustion engine, simply by virtue of the higher pressure of the combustion reaction in the jet engine. The 'downside' for the jet engine is that to make the whole arrangement work fuel efficiently you have to be operating at a significant fraction of Mach, much faster than ground transport can manage safely. Hence, combustion engines rule the earth and jet engines rule the sky in the current paradigm.
So, even assuming unlimited power supply, you would still have to have to have a very efficient motor on an energy cost-efficiency basis. To boot, you would have to have an engine that operated at similar cruise velocities. Even leaving aside infinite power generation, we can still consider that more time in the air is a longer time-frame along which the aircraft must be energy self-sufficient, generally equating to more mass in battery and/or power generation. More mass lowers the mechanical efficiency on an aircraft operation basis, because it is more energy you have to spend to accelerate and decelerate the extra mass.
So in an electric motor driven equivalent, you probably still have something resembling a turbo-fan. Except that your motor is primarily driving your compressor fan, and the turbine is there mostly to recapture some of the energy of compression (which also generates heat) into energy to drive certain engine functions like coolant and lubrication circulation, possibly some power regeneration. So probably a smaller turbine, but this puts you up against the inconvenient fact that compressing air is not very energy efficient as a means of generating thrust. If it were, we'd be running aircraft off compressed air.
What this generically gets at is that the electrification of air travel is likely not to resemble current jet-era technology. It's within the bounds of known technology to apply efficiency of electric motors to the problem of air transport, but the resulting architecture is likely to be very different, much as the fundamental architecture of a full EV is different than a gas automobile. This will likely in addition mean some fundamentally different infrastructure.
E.g. much of the energy of a flight is taken up in the initial acceleration, so it's possible that an Aerial EV would take off from a runway that more resembles that of an aircraft carrier than a flat road, with an assisted launch. Similarly, recapturing the energy on landing could again utilize a system more similar to those seen on aircraft carriers, only dedicated to regenerative capture rather than rapid deceleration.
More directly, though, the fundamental problem is generating thrust at near-Mach speeds. The efficiency of electrical motors at turning electrical power into rotational mechanical power is somewhat mitigated by subsonic and supersonic fluid mechanics, because an aircraft has to generate thrust by accelerating an airflow, or 'pushing' against air in some way or another. At these speeds, propellers basically start to lose their efficiency, and propulsion methods above these speeds therefore rely on the expansion of gasses with the transfer of heat into the gas. So to compete in these speed areas, an energy efficient means of transferring heat to (compressed) airflow has to be devised, which is very different than simply applying known electric motor technology.
Well the thing we need to start consideration is that jet engines are capable of providing a very high amount of thrust, yet they function on a simple principle of a gas turbine. Somehow it is possible to make an electric engine for propulsion but it will be complex and very heavy and lower powered. The only way an electric engine would work is to replace the jet engine core with some electric motor sort of, that can rotate the fan disk, creating thrust; however, considering how much torque is required to spin it in order to generate reasonable thrust is a nightmare, also the motor needs heavy batteries.
Yes, they could. As you said, assuming the power SUPPLY issue has been solved. At it's heart, a jet engine heats air, harnesses the expansion to drive a compressor and in most turbofans drive the "propeller". While presently all jet engines use burning fuel to produce that heat, the underlying principle of the system shouldn't care where the heat comes from. If you could dump enough energy through electric heaters in the combustion section of an otherwise standard engine, I think you could in theory operate the exact same engine off of electricity.
For a modern turbofan, that'd be about 35MW of power you'd have to dump into air heaters in the "combustion" section. This would be a pretty big engineering challenge, but I don't think it's out of the realm of possibility in theory. One option might be using plasma sparks, like an arc welder. Again, electrode lifespan would be an issue, but not necessarily impossible. Credit for this idea comes from this page:http://contest.techbriefs.com/2013/entries/aerospace-and-defense/3129
就我個人而言,我不認為電動商用飛機可以替代目前的噴氣發動機。也許最乾淨的航空旅行形式是使用碳中性生物柴油燃料驅動的當前高效噴氣發動機。