# Venturi Calculation for a Carburettor

1. Mar 4, 2013

Hi there, I am in my first year at uni studying aeronautical engineering and I am doing a group project where we have to design and build a carburettor.

We have to calculate the venturi size for the narrower section

The capacity of the engine is 166cc and it is 4 stroke
We are going to run the engine at 3600 RPM
The entrance and exit size of the venturi is going to be 22mm (size of the manifold)

Thats pretty much all we have to work on, so far I have tried to calculate the volume flow rate
and from that work out the mass flow rate of the air and then the mass flow rate of the fuel.

I could not find out how to calculate volume flow rate of a 4 stroke engine so I did this.

I divided 3600 by 60 to get RPS = 60 then divided that by 4 as only 1 every 4 strokes actually draws air in, to get 15 then multiplied that by the capacity 15 x 0.000166 to get 0.00249 metres cubed per second.
from this I multiplied it by the density of air to get the mass flow rate of air then divided it by 14.7 (stoichiometic ratio) to get the fuel mass flow rate.

I'm not sure if any of this is right and from here I am stuck. I do not know how to figure out the air speed for bernoulli's equation or how to figure out the pressure difference.

Any help would be much appreciated, I'm working in a big group and we are all struggling.

Thanks, Sacha.