[信息] 喷气发动机是如何工作的

发表于 2009-11-27 02:19:17 | 显示全部楼层 |阅读模式
How Do Jet Engine's Work?喷气发动机是如何工作的

        A jet engine works on the principle of Sir Isaac Newton's third law of physics, i.e. for every action there is an equal and opposite re-action. The action of forcing gases out from the rear of the jet engine results in a re-active force in the opposite direction, and is commonly referred to as 'thrust'. This thrust is measured in pounds force (lbf ), kilograms force (kgf ), or Newtons (N). Engines of this type are often referred to as 'Reaction Engines', a rocket engine being another example. Newton's third law and the action of a jet can be demonstrated in simple terms by inflating a balloon and releasing it, the escaping air propels the balloon in the opposite direction.

        Creating thrust takes energy. The energy required is obtained from burning fuels, whether it be in gas or liquid form such as propane, kerosine, diesel or even vegetable oils! This fuel is normally combined with pressurised air to increase the efficiency and power output for a given engine size. This fuel/air mixture is burned in some form of combustion chamber where the resulting hot gases expand creating an increase in pressure inside the combustion chamber. The expanding gases are then used to do useful work. One example of this process is what happens inside the cylinder of a car engine. Air and fuel are drawn into the cylinder by the downward movement of the piston, the piston then moves up and squeezes this mixture which is then ignited. The fuel burns creating a sudden sharp rise in pressure inside the cylinder. This pressure then forces the piston back down producing mechanical work. The piston then moves back up the cylinder to eject the burnt fuel ready for another cycle. This process is commonly referred to as the 'Suck, Squeeze, Bang, Blow' cycle! (SSBB).  
创建推力需要能量。所需的能量是从燃烧的燃料,无论是在气体或液体的形式,如丙烷,煤油,柴油,甚至植物油!这种燃料是通常结合加压空气,提高效率和功率给定发动机大小输出。这种燃料/空气混合物被烧毁,一些燃烧室形式,其中产生的热气体扩大创造一个燃烧室内部的压力增加。不断扩大的气体,然后用来做有益的工作。这个过程的一个例子就是内的汽车发动机汽缸发生。空气和燃料,是由各该活塞向下运动,活塞然后移动起来,这是挤出,然后点燃混合气进入气缸。燃料燃烧创造一个气缸内的压力突然急剧上升。这种压力迫使活塞则回落生产机械工作。活塞然后移动备份汽缸燃烧的燃料弹出另一个循环准备。这个过程通常称为'吸,挤压,爆炸,吹'循环! (黑带)。

 楼主| 发表于 2009-11-27 02:22:50 | 显示全部楼层
Comparison of the Operation of a Typical Jet Engine and a Four Stroke Internal Combustion Engine  比较典型的喷气发动机运行和四冲程内燃机

         The way a basic Turbojet engine burns it's fuel is exactly the same as in car engine, but instead of burning the fuel in discrete packets, the jet engine continuously sucks, squeezes, bangs and blows all at the same time! Also, instead of using the expanding gases to push on a piston, they are released through the turbine blades which takes some of the energy to drive the compressor, the rest being released to the atmosphere which results in 'Newtons' thrust described above. In a basic turbo jet, the air enters the front intake (suck) and is compressed by the compressor (squeeze), then forced into combustion chambers where fuel is sprayed into them and the mixture is ignited (bang). The gases which form expand rapidly, and are exhausted through the rear of the combustion chambers and out through the nozzle (blow) providing the forward thrust. Just before the gases enter the engine nozzle, they pass through a fan-like set of turbine blades  which rotates the engine shaft. This shaft, in turn, rotates the compressor, thereby bringing in a fresh supply of air through the intake. All of these processes are happening at the same time. Engine thrust may be increased by the addition of an afterburner section into which extra fuel is sprayed into the exhausting gases ( which contains surplus hot oxygen ) to give the added thrust.一个基本的方式涡喷发动机燃烧它的燃料是完全一样的汽车发动机,而是燃烧的哪类燃料,喷气发动机,不断吸,挤,爆炸和打击在同一时间!此外,而不是使用扩展气体推动活塞上,他们是通过涡轮叶片它利用了一些能量来驱动压缩机释放,其余被释放到大气中'的结果牛顿'上述重点。在基本涡轮喷气,空气进入前摄入量(吸吮),是由压缩机(挤压缩),然后将其中燃料燃烧喷入他们点燃的混合物(邦)商会强迫。这些气体的形式迅速扩大,并通过燃烧室,并通过喷嘴(打击)提供前进推力出后用尽。就在气体进入发动机喷嘴,他们通过一个风扇,这样的一套涡轮叶片转动轴发动机。这轴,反过来,旋转压缩机,从而在一个空气清新的供应将通过摄入。所有这些过程都发生在同一时间。发动机的推力可以由一个加力节在其中额外燃料消耗将增加气体喷除(其中包含剩余热氧),使增加的推力。

    At this point you may be asking yourself, "what actually makes it work?". When we effectively create a continuous explosion in our combustion chambers, what's to stop that explosion exiting the wrong way out of the compressor as opposed to out of the turbine? What is the physical explanation involved that will drive our engine ( and for that matter ANY jet engine ) the right way? The short answer to this is turbine to compressor 'Mechanical advantage'. For a slightly longer answer, I shall endeavour to explain below what it is and how it's used in a jet engine.

         Lets start with an experiment. Imagine we have a typical jet engine like the one in the diagram above, that isn't running. We inject a quantity of fuel in to the combustion chamber, ignite it and create a single explosion. If we haven't over egged the pudding and the engine is still in one piece, some of the gases from the explosion will have exited out of the compressor intake ( not what we want ), but most of the gases will have exited out of the exhaust. As a result we find that our single explosion has given us a small kick of forward thrust, but additionally and crucially, has given the engine's compressor/shaft/turbine assembly a small rotational 'kick' in the direction it would have in normal operation. If our intention was to design and build a one-shot 'pulse' jet then we have succeeded, the compressor/shaft/turbine assembly's rotational 'kick' being a bit redundant from a design point of view and actually detrimental from an efficiency point of view, but comes in handy later on as we shall see! ;o)
让任何一个实验开始。假设我们有一个像在上面的图一,这不是典型的喷气发动机运行。我们注入的燃料数量到燃烧室,点燃,并建立一个单一的爆炸。如果我们没有对煽动的布丁和引擎仍然是在一个片,从爆炸的气体,有些人已退出了压缩机的摄入量(不是我们想要的),但大部分的气体将退出出排气。因此,我们发现,我们的单爆炸,给我们提供了前进推力小球,但是另外更为关键的,给了发动机的压缩/轴/装配一个小型涡轮机转动'踢的方向'它会正常运行。如果我们的目的是设计和建造,以一杆'脉冲'飞机,我们已经成功,压缩机/轴/涡轮大会的旋转'踢'了一点,从设计的观点来看多余的,实际上是从效率点的不利意见,但就派上用场了以后,我们将会看到! ;海外)
 楼主| 发表于 2009-11-27 02:23:09 | 显示全部楼层
The reason the gases exit mostly out of the exhaust which is what we want for forward thrust and also gives us our small rotational 'kick', is exhaust turbine to intake compressor mechanical advantage. How it works is this: following our explosion, the gases try to go equally in opposite directions through the compressor and turbine wheels, and due to the specific orientation of their blades, also tries to rotate them in opposite directions. If the compressor and turbine wheels were exactly the same size and shape, then we would have the situation where the exhaust gases would exit from both ends equally,  generating equal forces in opposite directions resulting in no net thrust. Also, because the rotational forces acting on the compressor and turbine wheels  would be equal and opposite, and because they are both connected to the same shaft, the whole compressor/shaft/turbine assembly would remain stationary. But the compressor and turbine wheels are not the same. The turbine blades are generally at a 'steeper' angle than the compressor blades, i.e. their 'pitch' is greater, and the area through which the gases flow through the turbine is generally larger than the compressor. The result of this is that  the whole assembly is 'unbalanced' in terms of resistance to the explosion. What this means is that the gases will pass through the turbine more easily giving us our resultant net thrust in one direction, but equally importantly, because of the steeper blade angles of the turbine, the exiting gases give the turbine wheel more torque or 'turning force' in one direction than the compressor wheel's turning force in the opposite direction. The net result of these unbalanced torque's or turning forces is that the whole compressor/shaft/turbine assembly is given a rotational 'kick' in the direction that favours the turbine. This is the turbine to compressor mechanical advantage mentioned earlier that is employed in jet engines and is key to making them work! ;o)
的原因多半是排气这正是我们的前进方向,也赋予我们的小轮'踢'想气体出口,是进排气涡轮压缩机机械优势。它的工作原理是这样的:我们的爆炸后的气体尝试在相反的方向,同样通过压缩机和涡轮机车轮,由于其叶片明确的方向,还试图旋转方向相反他们。如果压缩机和涡轮机车轮都是一模一样的大小和形状,那么我们将有情况的废气将退出两端同样,在没有产生净推力产生相反的方向平等的力量。同时,由于部队在旋转压缩机和涡轮轮行动将是平等的,相反,因为他们都连接到同一轴上,整个压缩机/轴/涡轮大会将保持平稳。但是,压缩机和涡轮机车轮也不尽相同。通常在一个'陡'比压缩机叶片的涡轮叶片的角度,即他们的'球场'是更大的地方,以及通过它通过涡轮气体的流量一般较压缩机大。这样做的结果是,整个组合的'不平衡'的抵抗爆炸条件。这意味着该气体将通过涡轮更容易让我们产生的净推力我们的一个方向,但同样重要的是因为对涡轮叶片角度陡峭,该退出气体涡轮给予更大的扭矩或'转折点力'在一个方向比压缩机轮的转向相反方向的力量。最终的结果,这些不平衡力矩的,或把力量是整个压缩机/轴/涡轮组件都有一个旋转'踢的方向,有利于涡轮机'。这是机械的优势,以压缩机刚才是受雇于喷气发动机,关键是使他们的工作涡轮! ;海外)
        OK, so we made one explosion, got a short pulse of thrust and spun our compressor/shaft/turbine assembly a bit in the right direction. But hey, why not do this again, immediately following our first explosion with another explosion and then another, etc, in rapid succession, making the engine spin faster and faster? Well, we can do this but we have to wait a bit before we can create another explosion. Our first explosion used up the available oxygen in the combustion chamber and it needs to be refreshed. This is where our now free-wheeling/spinning ( as a result of our mechanical advantage ) compressor comes into play. As it spins, it pulls in fresh air from the outside and eventually replenishes the combustion chamber with a charge of fresh air/oxygen. We can now inject more fuel, create our second explosion and get a second 'kick' of thrust. If we time things right, we can get our second explosion to add to the already spinning compressor/shaft/turbine and make it spin faster than before.  We can repeat this process, creating our explosions more frequently as the compressor spins faster and faster, recharging the combustion chamber ever more quickly. Additionally, because of the ever increasing in-rush of air from the compressor, we find there is less and less tendency for our explosions to exit out of the compressor because of the ever increasing pressure barrier coming from that direction. Note also that so far our jet engine is still working discretely, i.e. it is still operating on the SSBB cycle as used in a car engine. Eventually though,  there will come a point when our compressor is spinning so fast that it recharges the combustion chamber almost instantaneously, the pressure barrier it creates as a result of the in-rush of air means that our explosions exit fully out through the turbine only, and finally, our explosions are now so close together that we have left the discrete SSBB cycle behind and are indistinguishable from the continuous roar of a typical jet engine! ;o)
行,所以我们一起爆炸,得到了短脉冲推力的旋转压缩机和/轴/涡轮的装配在正确的方向位。但是,好端端的,为什么不这样做了,紧接着我们的第一次爆炸与另一个爆炸,然后又等,接二连三地,使发动机旋转速度越来越快?那么,我们可以做到这一点,但我们稍等一会才能创建另一个爆炸。我们的第一次爆炸中使用了燃烧室提供氧气,它需要被刷新。这就是我们现在free-wheeling/spinning(由于我们的机械优势的结果)压缩机发挥作用的地方。由于旋转时,拉着新鲜空气从外面,最终会补充的新鲜空气充/氧气的燃烧室。现在,我们可以注入更多的燃料,创造我们的第二次爆炸并获得第二个'踢的推力'。如果我们的时间正确的事情,我们可以得到我们的第二次爆炸添加到已经旋转压缩机/轴/涡轮旋转,使之比以前更快。我们可以重复这一过程中,我们的爆炸造成更频繁的压缩机旋转速度越来越快,充电燃烧室更加迅速。此外,由于不断增加,空气压缩机繁忙的,我们发现有越来越少的趋势,爆炸退出的原因是由于不断增加的压力,从这个方向开来的障碍压缩机了。还要注意的是,迄今,我们仍是喷气发动机工作不连续,也就是说,它仍然在黑带周期运行在汽车发动机使用。刚开,随之而来的一个点时,我们的压缩机是旋转快,使燃烧室的充电,几乎在瞬间,压力屏障它作为结果,空气繁忙造成爆炸,意味着我们的出口,通过涡轮充分,是否只,最后,我们的爆炸事件都已经非常接近的合作,我们已经离开了离散黑带周期的后面,是从一个典型的喷气发动机的轰鸣声不断区分! ;海外)
        Although it is possible in theory to start a jet engine with discrete explosions, it would not be a very practical way to do it but more importantly would more than likely be a very destructive process! Normally the compressor/shaft/turbine is spun up either electrically, or pneumatically to a speed that sees enough in-flow of air from the compressor to make a decent pressure barrier, at which point enough fuel is introduced and burned so that it can take over from the 'starter motor'. This is the point at which the engine can be said to be 'self-sustaining' or 'idling'.
发表于 2009-11-28 22:14:54 | 显示全部楼层
您需要登录后才可以回帖 登录 | 注册


辽公网安备 21100402204006号|科技网 ( 辽ICP备07501385号-1   

GMT+8, 2019-9-17 07:04

Powered by tech-domain X3.4 Licensed

© 2001-2017 Comsenz Inc.

快速回复 返回顶部 返回列表