作者: Triumph (ELF-htx976) 看板: NSR
標題: Re: 澎漲室的大小怎麼計算呢？
時間: 東吳機研站 Wed Jun 18 02:48:04 2003
※ 引述《nitram (Blue)》之銘言：
: 就是若排氣量一定～該怎麼設計澎漲室的大小呢？
: Q1:若排氣量為100CC 那澎漲室的體積該為多少呢？
: 請作答...
: 感謝您花時間解題～謝謝 ^^
以上摘錄自相關書籍,我也沒有一個字一個字看完,如果你有興趣自己設計,甚至製造
排氣管,只能跟你說聲加油...因為理論與實際差距頗大...你要先清楚了解引擎的狀態,
才能針對不足處加以補強,一般來說,較大的膨脹室搭配較短的收縮部分,著重加速..
因為迴壓較小,氣流快速排出.而較小的膨脹室褡配較長的收縮尾,著重尾速...你看2T
250或500的車子就能瞭解.舉例像NSR500,你應該看過沒裝整流罩時候的照片吧,它的
排氣管是兩隻加速型搭配兩隻尾速型,這樣才能全速域都兼顧.然而2T125或150的單缸
車種,就只能看需求來設計了...還有進排氣角度及氣量,排氣口高度,形狀,...太多需要
考量的...就算製造出一隻優良的排氣管,還要考慮引擎能否承受...據說鐵駒海平兄就
曾經打出一隻NSR的排氣管,結果裝上它的大改比賽NSR都稱不了多久...為什麼呢..??
因為轉速直達15,000轉,跟本不是NSR這顆氣缸能承受的...總之有太多複雜的因素要考量
...文章裡面也說:即使理論看似簡易,但要最適化膨脹室的設計,是"very difficult",且
大型製造商仍在改良膨脹室設計,即使已經經過"30年"...另外講到比較詳細設計的書更是
複雜..它簡化排氣管為七段:
L1=Lt*L2/2
L2=D2/2*cot A2
L3=D1*6 to 11
L4=(D1*D2)/2*cot A1
L5=L1*(L3+L4)
L6=(D2+D3)/2*cot A2
L7=D3*12
D1=exhaust port area diam
D2=[6.25*(d1)^2]^1/2
D3=D1*(0.58~0.62)
where
Lt=tuned lean in inches
E0=exhaust open in degrees
Vs=sonic wave speed(1700 feet per second)
N=crankshaftRPM
裡面用到cotangent,排氣口直徑,傾銷角度,音速,曲軸轉速...一堆..
還有圖實在太難畫了...所以沒畫出來..
總之,加油吧..
The exhaust system and the expansion chamber
The exhaust system is one of the most important parts in modern two-stroke
tuning. In the beginning, the exhaust system was just a straight pipe, built
to transport the burnt gases out of the cylinder. Then some engineers realized
that the pipe, if it is correctly designed, could help to scavenge the cylinder
of burnt gases. This design is based on simple wave theory, that is the waves
behave as sonic waves which travel down the pipe at a speed that always equals
the speed of sound. This is about 510 m/s in hot exhaust gas. To understand
the function of the system, we must know how the waves behave when they are
being reflected in some way. If the wave sees an open end, it is reflected
back with inverted sign1. After the reflection it has the same period but the
amplitude may be reduced. If the end is closed, the sign is not changed, a
positive wave stays positive.
As the exhaust port is opened, a positive pressure wave [Here positive wave
denotes a pulse with overpressure, pressure higher than the surroundings and
of course a positive sign], or pulse, starts to travel down the pipe. When
it reaches the diffuser it reacts just as if it had reached an open end, i.e.
most of the wave is reflected and inverted. When the reflected pulse reaches
the exhaust port, which is still open, it assists to evacuate the cylinder
from burnt gases and to pull the fresh mixture up through the transfer ports.
At this time the rest of the pulse, which was not reflected at the diffuser,
reaches the reverse cone and sees this as a closed end. It is reflected as a
still positive pulse. This pulse reaches the exhaust port just in time to
push the fresh mixture, which has slipped out through the port, back in
before the piston skirt closes the port. According to the theory of waves,
two waves can meet and pass each other, without affecting each other.
Even if it looks easy in theory , it is a very difficult task to optimize
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
the expansion chamber. Big manufacturers' are still, after more than 30
~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
years of development, updating the expansion chambers on their production
~~~~~~~~~~~~~~~~~~~~
racers.One problem with the exhaust system on a two-stroke engine is that
this configuration is difficult to make silent, because a big silencer with
high resistance would deteriorate the function of the expansion chamber.
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※From: 東吳機研 scumotor.com.tw Triumph From 221202.D14-221.ncu.edu.t ...
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