专开帖子讲讲为什么涡轮增压省油

[Melee]

内燃机的热效率跟主要取决于空气的压缩比和燃烧温度
两个因素都是正相关
这也是为什么柴油机比汽油机省油的原因
船用低速柴油机热效率可达50%以上，自然吸气的汽油机只有30%多
汽油机加装涡轮增压后，效率可达40%以上
下图是理想奥托循环的PV图，纵轴是压力，黑线中黄色的面积为有用功，看见压力越高有效功越大，效率越高

[geniushanbiao]

单纯压缩比，涡轮机比自吸的要低，因为要防爆震。涡轮机只是比自吸的进气量大而且可调范围更大，不存在压缩比更高的事。

我估计你想表达的意思是涡轮机点火时候缸内压力高，这是事实，但说明不了什么问题。

[seymour]

Turbo engines generally have lower compression ratio as the intake air is hotter after being compressed. However, it has a smaller displacement thus requires less fuel during low load stages such as cruising. In other words, the turbo engine is more efficient compared to a bigger NA engine when the turbo is not running. Turbo engines can be understood as displacement on demand.

内燃机的热效率跟主要取决于空气的压缩比和燃烧温度
两个因素都是正相关
这也是为什么柴油机比汽油机省油的原因
船用低速柴油机热效率可达50%以上，自然吸气的汽油机只有30%多
汽油机加装涡轮增压后，效率可达40%以上
下图是理想奥托循环的PV图，纵轴是压力，黑线中黄色的面积为有用功，看见压力越高有效功越大，效率越高

[leuning]

Mazda 的技术才是增大压缩比。

[geniushanbiao]

Turbo engines generally have lower compression ratio as the intake air is hotter after being compressed. However, it has a smaller displacement thus requires less fuel during low load stages such as cruising. In other words, the turbo engine is more efficient compared to a bigger NA engine when the turbo is not running. Turbo engines can be understood as displacement on demand.

准确地讲，其实就是有一个更大的调节进气量的空间。

[Riikanbkk]

内燃机的热效率跟主要取决于空气的压缩比和燃烧温度
两个因素都是正相关
这也是为什么柴油机比汽油机省油的原因
船用低速柴油机热效率可达50%以上，自然吸气的汽油机只有30%多
汽油机加装涡轮增压后，效率可达40%以上
下图是理想奥托循环的PV图，纵轴是压力，黑线中黄色的面积为有用功，看见压力越高有效功越大，效率越高

很久没认真看过了，粗略提一下精神糊涂说一下，感觉做工分有用功无用功，涡轮压气也是个很恐怖的动力，100,000rpm 叶尖超音速mach1 - mach2，但这个只是为了发动机压气呼吸，对人没做功意义，算是无用功吧；那么等于 P线起点不是0，而是如你说的：涡轮进口压力和出口温度。所以实际燃烧热效还是=静压比CR与增压关系较小。而单说涡轮增压加力的效率基本取决于中冷效果和进气温度。

[Melee]

单纯压缩比，涡轮机比自吸的要低，因为要防爆震。涡轮机只是比自吸的进气量大而且可调范围更大，不存在压缩比更高的事。

我估计你想表达的意思是涡轮机点火时候缸内压力高，这是事实，但说明不了什么问题。

你怎么总是胡说
涡轮机的压比高于自吸、因为涡轮已经增压了，有个乘数效应
至于爆缸，并不是问题，因为涡轮排气有一个冷却，在进入汽缸前把温度降下来
所以涡轮增压发动机有压比高的好处，但没有温度高的问题

[Melee]

很久没认真看过了，粗略提一下精神糊涂说一下，感觉做工分有用功无用功，涡轮压气也是个很恐怖的动力，100,000rpm 叶尖超音速mach1 - mach2，但这个只是为了发动机压气呼吸，对人没做功意义，算是无用功吧；那么等于 P线起点不是0，而是如你说的：涡轮进口压力和出口温度。所以实际燃烧热效还是=静压比CR与增压关系较小。而单说涡轮增压加力的效率基本取决于中冷效果和进气温度。

正解
从P-V图上看涡轮增压相当于提升了起点，带来的汽缸进气温度上升可以通过中冷解决
从能量守恒的角度看，涡轮利用了排气余热，把这部分废热转换为进气压力，是有利于效率提高的

[Melee]

You don’t know there is a thing called intercooler which cools the air discharged from the turbo

Turbo engines generally have lower compression ratio as the intake air is hotter after being compressed. However, it has a smaller displacement thus requires less fuel during low load stages such as cruising. In other words, the turbo engine is more efficient compared to a bigger NA engine when the turbo is not running. Turbo engines can be understood as displacement on demand.

[seymour]

You don’t know there is a thing called intercooler which cools the air discharged from the turbo

Of course, without an intercooler, a 2.0 L turbo will give the same amount power as a 1.9 L NA. It is easy to understand that no practical size intercooler can actually cool all the way to ambient. There are air-cooled and liquid-cooled intercoolers. For liquid-cooled intercooler, you pray it actually have a dedicate cooling loop completely isolated from the engine cooling loop. Even in that case, the coolant temperature will still be quite a bit higher than ambient and the charge air temperature is necessarily higher than the coolant temperature.

[seymour]

你怎么总是胡说
涡轮机的压比高于自吸、因为涡轮已经增压了，有个乘数效应
至于爆缸，并不是问题，因为涡轮排气有一个冷却，在进入汽缸前把温度降下来
所以涡轮增压发动机有压比高的好处，但没有温度高的问题

It does not make sense to multiply turbo compression with the compression ratio of the engine. The only part that performs work is the power cycle, where the engine goes from TDC to BDC. The power cycle does not expand all the way to original air volume. Yes the exhaust runs the turbo, which does the pre-compression and, in a sense, it is waste work as it is not running the crankshaft.
Just think a 2.0L turbo does not give you better mpg than a 2.0L NA. It only gives you better mpg than a 3.5L NA if you drive gently. You can rewrite the efficiency expression using temperature ratio rather than compression ratio. The limiting factor is the pre-ignition temperature, which is your Th. This can not be changed for a gas engine unless you burn ethanol or 100 octane gas. The Tl increased as your intercooler is not infinitely large.

[Melee]

学点热力学再来扯吧
整个现代航空业就是建立在涡轮增压的基础上
你比NASA还懂

It does not make sense to multiply turbo compression with the compression ratio of the engine. The only part that performs work is the power cycle, where the engine goes from TDC to BDC. The power cycle does not expand all the way to original air volume. Yes the exhaust runs the turbo, which does the pre-compression and, in a sense, it is waste work as it is not running the crankshaft.
Just think a 2.0L turbo does not give you better mpg than a 2.0L NA. It only gives you better mpg than a 3.5L NA if you drive gently. You can rewrite the efficiency expression using temperature ratio rather than compression ratio. The limiting factor is the pre-ignition temperature, which is your Th. This can not be changed for a gas engine unless you burn ethanol or 100 octane gas. The Tl increased as your intercooler is not infinitely large.

[Riikanbkk]

Of course, without an intercooler, a 2.0 L turbo will give the same amount power as a 1.9 L NA. It is easy to understand that no practical size intercooler can actually cool all the way to ambient. There are air-cooled and liquid-cooled intercoolers. For liquid-cooled intercooler, you pray it actually have a dedicate cooling loop completely isolated from the engine cooling loop. Even in that case, the coolant temperature will still be quite a bit higher than ambient and the charge air temperature is necessarily higher than the coolant temperature.

我的FMIC 气冷一直比气温高不多，便宜土国货。你有几个严重误区：
（1）2.0涡轮 战斗力起码相当于4.0NA。实际会超过6.0NA。你可以看看WRC，LMP等等各类竞赛的规则，一般增压车要把排量x2.0-3.0，不然对同一个class 的NA太不公平。一般corolla，civic上面的小小发动机，只要塞涡轮改装，都可以轻松跑个500-600飞轮马力。

（2）气冷涡轮是效果最好的，原厂用水冷是因为机舱空间不足，必须用水冷节省空间。只要空间足够，不会有任何人在气体-气体循环使用效果低劣的液冷。

（3）我还从来没见过液冷涡轮居然是和发动机公用水路？！拜托这可不是变速箱制冷效果无所谓，中冷器直接决定了涡轮的力量。如果和发动机公用同一水路，管道小压力是不一样的，高压水泵你都不好接了。怎么接的压力单向阀？

（4）我的FMIC 气冷一直比气温高不多，便宜土国货。T国日常30-35℃ 进气40-50℃。如果我有钱弄稍好一点点的再改善下bonnet out duct，那起码日常买菜时效果完全可以过冷。注意自吸车进气也会比气温高得多！！！第一你的机舱比气温热得多，然后你的燃料流量一大温度也会高，然后你的进气自然会被机舱高温和烫手的进气管道热一点点。

另外，很多运动车上比如我的丰田Celica 原厂有高压水泵和一排喷头，水雾喷中冷散热片。也不需要很多水，只有最高出力时才需要，一壶水可以喷很久。如果偶尔用用的话，真的是严重过冷比环境温低好多！

另外虽然我非常看不起W2A，用液冷中冷给气体降温，最后也是用风扇气冷给液体散热，纯粹没事儿找事？。。。但是液体散热也有个好处，丰田这个车在WRC 比赛时因为规定必须按原厂设备，不能换气冷中冷所以效果很差，但是开赛时可以把W2A 中冷水箱里放满水，但是换热片箱里没有水，全都是干冰。LOL 这个开赛时的进气温度应该是恐怖的低温过冷，压气机增压效率瞬间爆表近100%

[seymour]

Just to remove the confusion in the most plain language. The efficiency of an ideal otto cycle is 1-1/R, where R is the compression ratio. (V_BDC/V_TDC). This efficiency is neither a function of the pressure nor a function of the temperature. Thus it does not care what pressure the intake stoke has. However, the air entering into the cylinder is hotter in a turbo engine. Most car manufacturers will build turbo engines with lower compression ratio to avoid going over preignition temperature. The CR can be easily looked up online.

内燃机的热效率跟主要取决于空气的压缩比和燃烧温度
两个因素都是正相关
这也是为什么柴油机比汽油机省油的原因
船用低速柴油机热效率可达50%以上，自然吸气的汽油机只有30%多
汽油机加装涡轮增压后，效率可达40%以上
下图是理想奥托循环的PV图，纵轴是压力，黑线中黄色的面积为有用功，看见压力越高有效功越大，效率越高

[seymour]

学点热力学再来扯吧
整个现代航空业就是建立在涡轮增压的基础上
你比NASA还懂

It is jet fuel not turbo that gives jet engine better efficiency. The idea of turbo is to produce more power with a smaller engine.

[off]

内燃机的热效率跟主要取决于空气的压缩比和燃烧温度
两个因素都是正相关
这也是为什么柴油机比汽油机省油的原因
船用低速柴油机热效率可达50%以上，自然吸气的汽油机只有30%多
汽油机加装涡轮增压后，效率可达40%以上
下图是理想奥托循环的PV图，纵轴是压力，黑线中黄色的面积为有用功，看见压力越高有效功越大，效率越高

有没有笔误？

[seymour]

（3）我还从来没见过液冷涡轮居然是和发动机公用水路？！拜托这可不是变速箱制冷效果无所谓，中冷器直接决定了涡轮的力量。如果和发动机公用同一水路，管道小压力是不一样的，高压水泵你都不好接了。怎么接的压力单向阀？

I believe the single-loop design is to share the reservoir but use a separate radiator and pump. The radiator cools down the coolant before the coolant enters the intercooler. It is to reduce cost for mild boost turbo.

[Riikanbkk]

I believe the single-loop design is to share the reservoir but use a separate radiator and pump. The radiator cools down the coolant before the coolant enters the intercooler. It is to reduce cost for mild boost turbo.

（1）涡轮水路较小，使用细管道，至少同时要走两个散热片和换热箱，需要的压力非常非常高！

（2）车用正时水泵是大流量低压力。远远不到中冷器的最低要求，带不动的，水流量往接近零。

（3）车用中冷水泵是极高的压力扬程和较小的流量。当然你肯定可以混用分配，但是平衡的计算要很头大，或者要定压单向阀。我是没见过公用水路的车，这和暖气、变速箱不一样，这个有大流量和远远超出发动机水路压力的供应要求。当然我知道肯定可以用，但是毕竟从来没见过有这样的，所以还是非常非常好奇感兴趣plumbing details nitpicks。毕竟你要用低压发动机水泵根本带不动旁路中冷，串联就更完球了；但是你要把高压水打进发动机也是一场灾难，第一就伤害水箱水泵缸垫（发动机水泵叶形不能串联，水箱强度差，水箱盖有低压泄压阀防水，对于所有的gasket 密封性能是加倍的考验），第二发动机水路无法承受高压。所以肯定只能要么加倍精确计算水路平衡fine tune， 要么就只能是有趣的调压单向阀？控水流和压力方向。

LOL 当然我知道肯定可行不会太过难，只是作为一个plumbing 爱好者和平衡专精，对此感觉很新奇有兴趣。

----
自己看看，中冷水泵是和辅助水泵完全不同的水泵。即使我那丰田老掉牙的1994年小破车水泵，压力扬程轻松压倒所有辅助水泵2倍



注意中冷的阻力，远远超过了发动机水路阻力好几倍

[Melee]

这是不懂装懂到极点了
燃料跟热机的效率没有关系
热机的理论效率（isentropic, adiabatic) 只跟压比有关系
实际效率考虑跟压比和涡轮入口温度正相关

求您了，去翻翻热力学的课本吧，要不去NASA的网站学学也行

It is jet fuel not turbo that gives jet engine better efficiency. The idea of turbo is to produce more power with a smaller engine.

[Melee]

有没有笔误？

没有
内燃机的热效率很少有超过50%的，除了少数低速柴油机，这些柴油机压比极高、冲程很长
连最先进的航空发动机，也很少能达到50%的效率
说白了，大部分的化学能浪费了
这就是为什么内燃机车碳排放高于电车的原因
现代燃气轮机联合循环发电，热效率可达60%以上，电车损失很少