Martin_534 píše: raddy píše:
Martin_534 píše:no možná, že to počítáme blbě :-)
nemělo by se to počítat s tlakem turba 0?
pak by to vycházelo na 15,8lb/ft pro ca a 17,4lb/ft pro sr
vždyt když chci spočítat, kolik vzduchu mi nasaje samotnej motor, tak by mělo bejt turbo odpojený
urcite nie, pocitame to spravne, pre 2l motor to vychadza okolo 40lbs/min, na 100%. Tlak turba vobec nie je zahrnuty vo vypocte prietoku.
pak se ale koukni do tohodle kalkulátoru http://www.bsmotor.com/turbo/kalkuler.html
a uvidíš, že to s tlakem počítá
Pardon, pomylil som sa, samozrejme sa pocita s tlakom turba, ale je to tlak prepocitany na ABSOLUTNY, tu je popis vzorca, ked si to preratas, vyde to tak isto:
Engine Volumetric Flow Equation
This equation is for finding the volume of air going into the engine. The displacement on our cars is 231 cu.in. We have a four stroke engine; the intake valve on a cylinder opens once every 2 revolutions of the engine. So, for every 2 revs the engine takes in 231 cu.in. of air. How many pounds of air is that? That depends on the pressure and temperature of the air in the intake manifold. But the volume is always 231 cu.in. every 2 rpm.
volume of air (cu ft/min)= engine rpm x engine cid
(1728 x 2)
Ideal Gas Law/Mass Air Flow
The Ideal Gas Law is a handy equation to have. It relates the air pressure, temperature, volume, and mass (ie, pounds) of air. If you know any three of these, you can calculate the fourth. The equation is written:
where P is the absolute pressure (not the gauge pressure), V is the volume, n is related to the number of air molecules, which is an indication of the mass (or pounds) of air, R is a constant number, and T is the absolute temperature.
What are absolute temperature and pressure? Do we care? Of course we do!
Absolute pressure is the gauge pressure (measured by a gauge that reads 0 when it is open to the outside air) plus atmospheric pressure. Atmospheric pressure is about 14.7 psi at sea level.
Example: a boost gauge reads 0 psi before it is hooked up. Hook it up, boost the car, and it reads 17 psi. 17 psi is the gauge pressure, the absolute pressure at sea level is 14.7 + 19 = 33.7.
A pressure reading is marked psia or psig. The "a" stands for absolute, the "g" for gauge. (The psi stands for Pounds per Square Inch). As we just showed, 17 psig = 33.7 psia. A perfect vacuum is 0 psia, or -14.7 psig.
The absolute temperature is the temperature in degrees F plus 460. This gives degrees Rankine, or deg R. If it is 80 deg F outside, the absolute temperature is 80 + 460 = 540 deg R.
The Ideal Gas Law can be rearranged to calculate any of the variables. For example, if you know the pressure, temperature, and volume of air you can calculate the pounds of air:
That is useful, since we know the pressure (boost pressure), the volume (which we calculate as shown in the first section "Engine Volumetric Flow"), and we can make a good guess on the temperature. So we can figure out how many pounds of air the engine is moving. And the more pounds of air you move, the more power you will make.
Here is the Ideal Gas Law rearranged to the two handiest forms, with the required constants:
To get pounds of air:
n(lbs/min)= P(psia) x V(cu.ft./min) x 29
(10.73 x T(deg R))
To get the volume of air:
V(cu.ft./min) = n(lbs/min) x 10.73 x T(deg R)
(29 x P(psia))