Knowing Mass Flow Rate

What's the pressure?

that is the singel cylinder engine & i want to know air fuel mixture require

The fluid velocity times the cross sectional area of the pipe. At least that's how it's done for industrial ventilation requirements.

If you use an air flow meter based on the thermal properties of the air, the output will be proportional directly to the mass flow rate.

Other air flow sensore measure the volume flow rate and you will need to know the temperature and pressure of the air to calculate the mass flow rate.

Much easier to use a sensor that measures mass flow directly using the thermal microbridge sensor arrangement.

John.

is there any formula to know mass flow rate

Mass Flow Rate= density of fluid X velocity X cross sectional area

This is true....

density is easy ( density = preesure / temp * gas constant)

so is cross sectional area, since it is basically constant

but how does one know the velocity?

hot wire anemometers are great, but often expensive. Usually velocity is measured by differential pressure. either a pitot probe or pressure sensors at the entrance and throat of a venturi.

I can't find Janna, since I am moving into my house and books are still boxed up. I can find Zucrow, but am not familiar enough with him to find it and I dont think he concerns himself with measurement anyway. But according to Mark's Handbook, pg 3-63, volume flow is :

Q = C * E * Y * A2 * sqrt( 2* dP/ rho1)

Q is volume flow rate

C is a discharge coefficient that depends on the exact geometry of the venturi but is pretty close to unity (.984~.995)

E = 1/sqrt(1-beta^4)

beta = d/D

d = venturi throat diameter

D = upstream pipe diameter

Y= sqrt[(k*r^(2/k)*(1-r((k-1)/k))*(1-beta^4))/((1-r)*(k-1)(1-beta^4*r^(2/k)))]

r = pressure at throat/pressure upstream

k = ratio of specific heat = 1.4 for air

A2 = venturi throat area

dP = change in pressure between throat and upstream inlet

Rho = density at venturi inlet temperature and pressure

with the right pressure sensors that will probably get you into 10% accuracy range without calibrating the meters. In cars they typically get the high precision they need by closing the loop on oxygen concentration in the exhaust. That allows them to correct for any variation in sensors, venturis, fuel injector nozzles, or whatever.

I hope this helped