进气温度的一点计算

mianhuatang

今天和一群傻瓜美国人讨论车，很多人说cold air intake真得能提升20马力，顽固得要死，于是我就写了个计算，统统服了。贴过来分享以下，先是中文翻译版本，翻译得不好，后面是我的英文版原文。。。因该会比较精确一些。。。



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进气温度 (IAT) vs.马力 (HP)

理想气体定律说明，理想气体的密度可以表示成 , P
绝对气压, R
气体常数，T
为绝对温度 (凯尔文) [1], 均为SI体系参数。

对于理想干燥气体,
R=287.05J/(kg k)


[2], 于是可以写出下表

Density (Kg/m^3)
	Pressure (bar)
IAT (Celcius)	1	1.25	1.5	1.75	2
-10	1.32	1.65	1.99	2.32	2.65
0	1.28	1.59	1.91	2.23	2.55
20	1.19	1.49	1.78	2.08	2.38
40	1.11	1.39	1.67	1.95	2.22
50	1.08	1.35	1.62	1.89	2.16
60	1.05	1.31	1.57	1.83	2.09
65	1.03	1.29	1.55	1.80	2.06
70	1.02	1.27	1.52	1.78	2.03
75	1.00	1.25	1.50	1.75	2.00
80	0.99	1.23	1.48	1.73	1.97
90	0.96	1.20	1.44	1.68	1.92
100	0.93	1.17	1.40	1.63	1.87
120	0.89	1.11	1.33	1.55	1.77

受限于理想气体定律 N = (V/K) (P/T)

N是气体中的分子数量, V 为体积, K 是通用气体常数除以啊福加德罗常数, P 为压力，T 绝对温度 [3]. 所以 . 因为 (V/K)R

是常量 (用C代替), 所以 . 上表可以改写成,

Number of Molecule
	Pressure (bar)
IAT (Celcius)	1	1.25	1.5	1.75	2
-10	1.32C	1.65C	1.99C	2.32C	2.65C
0	1.28C	1.59C	1.91C	2.23C	2.55C
20	1.19C	1.49C	1.78C	2.08C	2.38C
40	1.11C	1.39C	1.67C	1.95C	2.22C
50	1.08C	1.35C	1.62C	1.89C	2.16C
60	1.05C	1.31C	1.57C	1.83C	2.09C
65	1.03C	1.29C	1.55C	1.80C	2.06C
70	1.02C	1.27C	1.52C	1.78C	2.03C
75	1.00C	1.25C	1.50C	1.75C	2.00C
80	0.99C	1.23C	1.48C	1.73C	1.97C
90	0.96C	1.20C	1.44C	1.68C	1.92C
100	0.93C	1.17C	1.40C	1.63C	1.87C
120	0.89C	1.11C	1.33C	1.55C	1.77C

空气成分是大约21% 的氧气，这个是不受限于气压和温度的[4]. 并且氧气是参加燃烧的唯一主要成分.

屁话说完.

对于一台在海平面的自然吸气的引擎，环境温度是20度，一般使用原厂的进气系统，进气温度大约是60度。参照上表，参与一次燃烧得分子数量为1.05C.

即使是最无耻的冷风进气系统生产厂生产的系统，也就是声称10度的降温，假设他们的声称是成立的话，对于同样一台车，参与一次燃烧的分子数量为1.08C.

1.08C 对1.05C 仅仅只有 2.9%的提升. 因此，假设这台车用原厂系统时产生200马力，那么使用那个“超级冷气进气系统”的话，也仅仅只能产生205马力，根本达不到号称的15马力提升。更不要说这只是理论计算，实际上还要打折扣。

除此以外，上面的那个表对自然进气vs. 增压引擎还有更特殊的意义。

例如仍旧使用上面例子里的那台车，200马力使用原厂进气。参与燃烧的分子数量是1.05C。如果有增压系统的话（无论是turbo还是supercharger），如果增压到1.5bar，那么再没有intercooler的情况下，进气温度可以达到100度，也就是说分子数量是1.40C。这是产生了33%的提升，同样的这台引擎就可以产生267马里。看上去还不错

但是如果使用比较高效率的intercooler，进气温度可以降低最多25度，也就是75度的进气温度，这是分子数量是1.50C，那么这个引擎可以产生285马力，对于一个不算太贵得intercooler来说，18马力已经很好了。

参考文献
[1] http://en.wikipedia.org/wiki/Ideal_gas_law
[2] http://www.engineeringtoolbox.com/humid-air-ideal-gas-d_677.html
[3] http://hyperphysics.phy-astr.gsu.edu/HBASE/kinetic/idegas.html
[4] http://www.physlink.com/reference/AirComposition.cfm








Intake Air Temperature (IAT) vs. HorsePower (HP)
Due to Ideal Gas Law, ideal gas density canbe identified as, where P
is absolute pressure, R
is specific gasconstant and T
is absolutetemperature (in Kelvin) [1], all units in SI unit system.

For ideal dry air, R=287.05J/(kg k)
[2], so the followingtable can be developed as

Density (Kg/m^3)
	Pressure (bar)
IAT (Celcius)	1	1.25	1.5	1.75	2
-10	1.32	1.65	1.99	2.32	2.65
0	1.28	1.59	1.91	2.23	2.55
20	1.19	1.49	1.78	2.08	2.38
40	1.11	1.39	1.67	1.95	2.22
50	1.08	1.35	1.62	1.89	2.16
60	1.05	1.31	1.57	1.83	2.09
65	1.03	1.29	1.55	1.80	2.06
70	1.02	1.27	1.52	1.78	2.03
75	1.00	1.25	1.50	1.75	2.00
80	0.99	1.23	1.48	1.73	1.97
90	0.96	1.20	1.44	1.68	1.92
100	0.93	1.17	1.40	1.63	1.87
120	0.89	1.11	1.33	1.55	1.77

Subject to Ideal Gas Law that N = (V/K) (P/T)
where N is the numberof gas molecule, V is the volume, K is universal gas constant divided byAvogadro’s number, P is pressure and T is absolute temperature [3]. Therefore . Because (V/K)R
is constant (representedas C), so
. The above table can be rewrote as,

Number of Molecule
	Pressure (bar)
IAT (Celcius)	1	1.25	1.5	1.75	2
-10	1.32C	1.65C	1.99C	2.32C	2.65C
0	1.28C	1.59C	1.91C	2.23C	2.55C
20	1.19C	1.49C	1.78C	2.08C	2.38C
40	1.11C	1.39C	1.67C	1.95C	2.22C
50	1.08C	1.35C	1.62C	1.89C	2.16C
60	1.05C	1.31C	1.57C	1.83C	2.09C
65	1.03C	1.29C	1.55C	1.80C	2.06C
70	1.02C	1.27C	1.52C	1.78C	2.03C
75	1.00C	1.25C	1.50C	1.75C	2.00C
80	0.99C	1.23C	1.48C	1.73C	1.97C
90	0.96C	1.20C	1.44C	1.68C	1.92C
100	0.93C	1.17C	1.40C	1.63C	1.87C
120	0.89C	1.11C	1.33C	1.55C	1.77C

Air consists of ~21% of Oxygen despite ofthe pressure and temperature [4]. Oxygen is the only major matter involved incombustion.

End of crap.

For a real world normally aspirated vehicleat normal sea level with operation ambient temperature of 20 degree Celsius,the factory intake air temperature is usually around 60 degree Celsius.According to above table, the number of molecule involved in one combustioncycle is 1.05C.

With the wildest claim of some cold airintake manufacture, the temperature drop can be as much as 10 degree Celsius.Assume it is possible, then the number of molecule in one combustion cycle is1.08C.

1.08C v.s. 1.05C is only 2.9% increment.Therefore, if the vehicle running factory intake is rated at 200HP, after the“extremely efficient” cold air intake mod, the horse power will be 205HP, only5 HP increase. In clear contrast against the claimed 15HP increase. This isjust theory calculated upper limit, in reality, the number will be even lower.

However, the above table is very useful forcomparison between normally aspirated vehicles vs. forced inductioncounterparts.

For example, using the above example,normally aspirated 200 HP vehicle with factory intake system. The number ofmolecule involved in one combustion cycle is 1.05C. If the vehicle is equippedwith forced induction system running at 1.5bar, normally the intake temperature(without intercooler) will be around 100 degree Celsius, posing a 1.40C number.The increase is 33%. So ideally it should generate 267HP. Looks pretty good.

However, with high efficiency intercooler,the air charge temperature can drop as much as 25 degree Celsius (75C intaketemperature), posing a different number of 1.50C. In this case the car shouldhave 285HP. 18HP is not bad at all for the extra intercooler.

Reference
[1] http://en.wikipedia.org/wiki/Ideal_gas_law
[2] http://www.engineeringtoolbox.com/humid-air-ideal-gas-d_677.html
[3] http://hyperphysics.phy-astr.gsu.edu/HBASE/kinetic/idegas.html
[4] http://www.physlink.com/reference/AirComposition.cfm

方正

Kenty

高深理论,,旁观,

edison

看了还是不懂。。。。。

thepen