Help with calculating air mass through throttle body/orifice
Help with calculating air mass through throttle body/orifice
(OP)
I am in the mindset right now of trying to model my engine and calculate various flow rates. What I'd like to do is make a calculator to show various rates of flow through the TB. I know it will be hard to determine the amount of opening anything other then full open/closed.
I'm at WOT, and I'm also boosted...
I have some info that I was reading that mentions Saint Venant equation to calculate the mass flow rate, using Ambient Air and Temp Upstream / PMan.
Can anyone give some help on how I can do this? I'd like to be able to get velocity, mass flow, and whatever else I can take from it as well.
Thanks!
I'm at WOT, and I'm also boosted...
I have some info that I was reading that mentions Saint Venant equation to calculate the mass flow rate, using Ambient Air and Temp Upstream / PMan.
Can anyone give some help on how I can do this? I'd like to be able to get velocity, mass flow, and whatever else I can take from it as well.
Thanks!





RE: Help with calculating air mass through throttle body/orifice
Most cars are somewhere around 80-90% efficient, which means that if a cylinder displaces 100cc, for example, there will be 80-90cc of air that enters that cylinder on every intake stroke. Of course, VE is different at different RPMs as well.
for boosted engines, just make sure to take into account the actual air pressure, ex 10 psi boost + 14.7psi atmospheric = 24.7 psi absolute pressure.
After that, there should be a formula or table somewhere that relates the different amounts of oxygen content per cubic foot of air at different temperatures and pressures. I have been looking for such a formula myself, actually, and havent found it yet.
Sorry if I just repeated what you already knew. I need that formula too!
RE: Help with calculating air mass through throttle body/orifice
mdot = 0.5*ρ*VEe*Vd*(1 + Pb/Pa)*N
ρ = air density
VEe = volumetric efficiency referred to intake manifold p & T
Vd = engine displacement
Pb = boost pressure
Pa = atmospheric pressure
N = engine speed
Leave out ρ to get volumetric flow rate. Watch your units.
RE: Help with calculating air mass through throttle body/orifice
RE: Help with calculating air mass through throttle body/orifice
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Help with calculating air mass through throttle body/orifice
RE: Help with calculating air mass through throttle body/orifice
I was looking for /2 and missed the X 0.5
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Help with calculating air mass through throttle body/orifice
RE: Help with calculating air mass through throttle body/orifice
input is pressure in mb (1000mb = sea level... i didnt even relize b was metric... makes sense though) temperature in C and dewpoint, as moist air is somewhat less compressable
http://wahiduddin.net/calc/density_altitude.htm
RE: Help with calculating air mass through throttle body/orifice
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Help with calculating air mass through throttle body/orifice
that is all. doesnt have a huge effect because air at earthly temperatures can only hold so much water before it just falls out of suspension i.e. dew.
you could probably ignore it for this purpose, i was just mentioning that the calculator includes it should you want to be ultra precise.
RE: Help with calculating air mass through throttle body/orifice
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules